PLYOMETRIC TREATMENT AND WHOLE-BODY MOVEMENT TIMES

PETER GARNET CROSS

SUBMIITED IN PARTIAL FULFllLMENT OF THE REQUIREMENT

FOR THE DEGREE OF MASTER OF SCIENCE

AT

DALHOUSIE UNIVERSIN

OCTOBER, 1 997

'.

Copyright by Peter Gamet Cross, 1997

National Librriry I*I of Canada Bibliothèque nationale du Canada

Acquisitions and Acquisitions et Bibliographie Sewices services bibliographiques

395 Wellington Street 395 rue Wellington Ottawa ON K1A O N 4 OttawaON KtAON4 Canada Canada

The author has granted a non- exclusive licence dowing the National Library of Canada to reproduce, loan, distribute or sell copies of this thesis in microfom, paper or electronic formats.

The author retains ownership of the copyright in this thesis. Neither the thesis nor substantial extracts fiom it may be printed or otherwise reproduced without the author's permission.

L'auteur a accordé une licence non exclusive permettant à la Bibliothèque nationale du Canada de reproduire, prêter, distribuer ou vendre des copies de cette thèse sous la forme de microfiche/film, de reproduction sur papier ou sur format électronique.

L'auteur conserve la propriété du droit d'auteur qui protège cette thèse. Ni la thèse ni des extraits substantiels de celle-ci ne doivent être imprimés ou autrement reproduits sans son autorisation.

ABSTRACT

The purpose of this study was to determine whether a plyometric

treatment of rapid knee lifts had a significant effect on subjects' sprint ninning

speeds.

The concept of a rapid muscle stretch of the stretch-shortening cycle (SSC)

that loads the eccentric elongation phase of muscular contraction to store

elasticized and reflex potentiated energies was investigated. This stored energy is

reused in the ensuing concentric contraction phase. A SSC exercise manifest as

rapid knee lifts was imposed on experimental subjects to stress the SSC for

possible potentiation effects.

A test sprint run of 60 metres (m) by both Experimental and Control Groups

was designed to elicit possible potentiation effects of the plyometric exercise

protocol of hip and knee flexor and extensor muscles, on their sprinting

performances.

Both treated and untreated groups were engaged in 60 m sprint running

speed tests at Mo-week intervals throughout the ten-week plyometric treatment

period.

Groups' split tirnes were recorded for average sprinting valocities V I and V2

over the 10 - 20m, and 20 - 60m distances. Initially, each group had fifteen

subjects, but at the end of the ten-week period of the study, attrition reduced

participation to 4 subjects in the Control Group, and 5 in the Experimental Group.

Statistical analysis by a two way ANOVA for repeated rneasures was

performed to detemine any intra- and inter- group interactions. Lac; ot cornplete

data from subjects for the five post tests reduced analyses to only two post tests,

and these were post tests 1 and 2. For Post Test 1, the four subjects of aie Control 4

Group, and five of the Experimental Group, in their V I and V2 average velocity

measurements over the 10 to 20 m and 20 to 60 m distances, showed increases in

their sprint velocities. With post test 2, V I and V2 had longer sprint split-tirnes,

and slower average velocities for both groups over aie previous Post Test 1

performance; the Control Group exhibiting higher average velocities in their pre

test sprint run. Only the 20 to 60 m 012) distance of sprint test 1 (p = 0.0293) was

within the (p < 0.05) statistical level of significance for the results. This was the

only statistically significant positive increase in post test sprint average velocities

over the Experimental Group and the Control Group's V2 averaged velocity sprint

values.

Results of this study indicate that the Experimental Group increased their

I average sprint velocity by 6.30 %, and the Controt Group had their average sprint

velocity lowered by 0.38 %. Reflex potentiations of the rapid stretches of th8 SSC

on hip and knee flexor and extensor muscles are the suspected causative factors

that possibly had a cumulative training effect on the legs' neuromuscuIar

adaptations to the increased stress of the plyometric exercise protocol.

ACKNOWLEDGEMENTS

I wholeheartedly wish to thank my thesis advisor, Dr. John Mc Cabe, for his t

untiring assistance, thoroughness and devotedness with advice in helping me to

complete this research study. My sincere gratitude also extends to the other

mernbers of my thesis cornmittee, Dr Phi1 Carnpagna (Chair), Dr. Carol Putnam

and Professor Nigel Kemp.

I also wish to thank our technician, MI. Dave Grimshire, without whose

steadfast and diligent assistance, this project would not have been completed.

Sincere thanks are also extended to the Staff of the Dalplex facility,

especially to Mr. Tony Martin, who gave permission to use the Dalplex indoor

track and field - house facility as the research venue, and also, to Mr. Dan Mc

Kenzie, who was personally responsible for cornplying with stringent

specifications for electrical and other mechanical installations in the sprint test

t run area.

Special thanks also to my son, Jason Gamet Cross, who did the graphs and

tables, and for his encouragement and assistance to help my completion of this

project.

TABLE OF COMENTS

CHAPTER 1 INTRODUCTlON

1.000 Sprint Training Methods

1.1 00 Overview of Sprint Training

1 .120 Interval Training

1.130 Strength Training

1.140 Supramaximal Training

1.150 Speed Training

1.1 60 Start Action Training

1 .1ïO Acceleration Training

1 .180 Skills Drills

1.1 90 Plyometrics

1.200 Sprint Training Methods

1.21 0 Functional Aspects of Sprint Training

1 220 National Level Training

1.230 Brent Mc Farlane's Method

1 240 Researcher's Sprint Training Methods

1.241 Speed Constancy Concept

1.242 Plyometric Training

1.300 Staternent of the Problem

1.400 Purpose of the Study

1.500 Null Hypothesis

1.600 Research Hypothesis 13

CHAPTER 2 REWEW OF THE LITERATURE 14

2.000 Rationale for Plyometric Training 14

2.1 00 Energy Storage Strategies 14

2.200 Neuromuscular Considerations 17

2.300 Training Techniques for the Stretch - Shortening Cycle 18

2.400 Thys et al., (1972) 'Utilisation of Muscle Elasticity in Exercise' 19

2.41 0 Asmussen and Bonde - Petersen's (1974a) 'Storage of Elastic

Energy in Skeletal Muscles in Man' 21

2.420 Asmussen and Bonde - Petersen's (1 974b) 'Apparent Efficiency

and Storage of Elastic Energy in Human Muscles During

Exe rcise' 23

2.430 Bosco and Komi's (1 979a) 'Potentiation of the Mechanical

Behaviour of the Human Skeletal Muscle

Through Prestretching' 27

2.440 Bosco and Komi's (1 981 ) 'Prestretch Potentiation of Human

Skeletal Muscle During Ballistic Movements' 30

2.450 Bosco, Komi and Ito's (1 982) 'Combined Effect of Elastic Energy

and Myoelectrical Potentiation During Stretch - Shortening

Cycle Exercises' 32

2.500 Generai Observations 36

CHAPTER 3 METHOOS AND PROCEDURES

3.000 Selection of Subjects

3.1 00 Length of Study

3.200 Attrition of Subjects

3.300 Testing Sessions

3.400 Testing Procedure

3.500 Physical Set-up of Research Area

3.600 Training Schedule

3.700 Wami Up Session

3.800 Plyometric Exercise Treatment

3.8 1 0 The Exercise Protocol

3.820 Rest Period Between Sets

3.830 Muscles Affected by the Plyometric Training

3.840 Muscles that go through the Stretch - Shortening Cycle of

the Plyometric Exercise

3.850 Ranges of Motions of Plyometrics and Sprinting

3.860 The Step and Stride of a Sprint Run

3.870 Plyometric Protocol for the Microcycles

3.900 The 60 metre Sprint Test Run

3.91 0 Data Collection

3.920 Statistical Procedures

CHAPTER 4 RESULTS

4.000 Overview

4.1 00 ANOVA Analyses

4.200 60 metre Sprint Test Runs

4.300 Plyometnc Rapid Knee Lifts

4.400 Summary of Results

4.500 Knee Lifts' Relatedness to Strïde Frequency

4.600 Post-Test 2 Average Velocity Decreases

4.700 Attrition of Subjects

CHAPTER 5 DISCUSSION

5.000 Overview

5.100 Anthropometric Data

5.200 Plyometrics of Speed Training Compared with Previous Studies

5.300 Implications for Further Study

5.400 Conclusion

APPENDICES

APPENDIX A. Experimental Group Data for all Subjects and Tests,

Mean Times for VI and V2

APPENDIX B. Control Group Data for al1 Subjects and Tests,

Mean Times for V I and V2

APPENDIX C. Concourse of the Dalplex lndoor Track, Showing

the Location of the Three Serially Linked Transrnitting-

Receiving-Recording Stations at the 10m, 20m and 60m

Distances

APPENDIX D. A Typical Monitoring Station with a Beam-Coupled ?

Transrniter-Receiver Linked to a Digital Electronic Clock

Timer (Somewhat Schematic and Not to Scale)

APPENDIX E. Consent Form

APPENDIX F. PAR - Q & YOU

LIST OF FIGURES

FIGURE 1. Graphed Results of Dataset for V I and V2

Average Velocities of Experirnental and Control Groups

FIGURE 2. Graphed Results of PlyometrÎc Knee Lift Frequency

Correlated with Stride Frequency for Three Tests

FlGURE 3. Graphed Results of Dataset for Pearson's

Correlation Coeficient Analysis of Knee Lifts with Stride

Frequency for 3 Sprint Test Runs

LIST OF TABLES

TABLE 1 a. Anthropometric Data for Experimental Subjects

TABLE 2a. Absolute Difference of Pre-Test's Average

Velocity with Combined Average Velocities for Post-Tests

1 and 2 of Experimental Group

TABLE 2b. Absolute Difference of Pre-Test's Average

Velocity with Combined Average Velocities for Post-Tests a

1 and 2 of Control Group

TABLE 3. Anova Summary, Enor Analysis by method

of Least Squares 58b

TABLE 4. Experimental Group Comparative Stride Frequencies

of the Knee Lift Protocol Matched with the Stride Frequency

of the 50m Sprint Run 58b

REFERENCES 76

CHAPTER 1

l NTROOUCTION

This thesis concems the study of a plyometric rapid knee-lift training protocol

that is intended to increase human whole-body movement velocities during sprint

running. The purpose of this study is to detenine whether plyornetric training of

fast limb movements has any effect on subjects' whole-body ninning speeds.

Plyometrics is "any exercise that uses the natural elastic recoil elements of human

muscle and the neurological stretch, or myotatic reflex that are inherent in al1

muscles to produce a stronger, faster muscle responsen (Chu, 1984). The

myotatic stretch reflex is a rate-sensitive reflex. If muscular eiongation occurs

quickly, a fast and powerful contraction occurs (Enoka, 1994), and it appears that a

slow stretch that produces insignificant torque will elicit negligible rnuscular

contraction (Bompa, 1993).

Sprint running is the fastest form of a person's natural movement. "Sprinthg

is a very natural movement but a fast sprint is not easy to analyse" (Delecluse et al.,

1992). In addition, sprinting is a motor skill that is enhanced through adherence

to sound motor leaming principles whose objective is to achieve the maximum

sprinting velocity as soon as possible (Gambetta, 1991). A number of factors that

affect sprint performance are the athlete's training status, reaction time, starting

technique, abilîty to maximize the acceleration phase with a continuous increase in

stnde length, and maintenance of the maximum velocity phase (Schubert, 1992). .. A sprinter's acceleration (rate of change of velocity) allows him / her to maintain

maximum speed in the shortest possible time, and sprinters, regardless of level

of performance, can reach maximum speed between 30 and 60 metres (m)

(Gambetta, 1991). A person's training status is inherent in their ability to utilize

and maintain maximum force of repetitive leg movements, combined with

frequency of the leg's striding action in coordination with their natural stride length

to obtain maximum sprinting speed. As a consequence, stride frequency times

length produces maximum sprinting velocity (Bompa, 1993; Gambetta, 1991).

These factors are contingent on the body's capacity to sustain tremendous lower

limb torques from acceleration to maximum velocity phase of the sprint run.

f Maximum speed demands high levels of neuromuscular coordination to run at the

highest possible velocity (Gambetta, 1991).

Cornpetitive sprint running takes place over short distances such as Som,

60m, 100m and 200m. For the 100m event, there are three phases, the

acceleration phase from O to 60m, the maximum velocity phase from 60m to 80m

and the deceleration phase from 8Om to 100m (Delecluse et al., 1992). The 60m

distance selected for this study encompasses the entire acceleration phase of a

subject's all-out effort at sprinting. This physiological limit of exertion of effort has

a firm metabolic basis, and corresponds to the distance-time for which the leg's fast

twitch muscle fibres can be maximally stressed by the muscles' anaerobic

metabolic fuel for fast hnritch fibres. Sprint ~ n n i n g uses the leg muscles' stretch-

shortening cycle (SSC) which potentiates additional elastic and myoelectrically

stimulated force in the sprinting action (Komi, 1978).

The quadriceps knee extensors, and the hamstrings knee flexors of the thigh

are the main propulsive locomotor muscles of the leg utilized in a sprint run.

Muçcular torques around hip, knee and ankle joints contribute to the efficient

translocation of muscular forces that aid in the cyclic motion of the stnde action.

Regardless of the training mode used to improve a subject's whole-body

speed, improvement in performance will occur from the body's forced adaptation to

enhance the training stimulus by implicit / explicit use of the training overload

principle (Bompa, 1993; Radcliffe and Farentinos 1985; Enoka, 1994). In sprint t

running, absolute whole-body velocity depends on selecting an optimum stride

length, while increasing the frequency of the legs' cyclic rotations. This maximizes

foot-implant generated force, increases flight time, while minimizing ground contact

time. The skilful coordination of maximal rotational torques for vertical and

horizontal accelerations of body-mass ensures optimum forward velocity.

From a maximum 100% kinematic performance of whole-body speed at

6.08 metres per second (rn/s), with corresponding stride length of 3.24m, and stride

frequency of 1.87 strides per second (Stls); a 50% reduction of this whole-body

velocity of 3.01 m/s, corresponds to a stride length of 1.97m (60%), and stride

frequency of 1.53 Stls (80%) (Personal observations). Stride frequency or rate of

limb motion is the parameter that is the most difficult to rectify by increased i modification of a training stimulus, as there is only a 20% possible incrernent as

cornpared with the other factors. As the most difficult factor to increase by

ordinary training methods, any fumer training method that stnves to increase

stride frequency, should warrant investigation, as this study has proposed.

A person establishes an optimal stride length that is suitable for their total

biornechanical profile. A stride is produced when duting a run, the same foot

again stnkes the ground, and repeats the ballistic extension - fiexion sequence of

the leg's stride cadence that involves the SSC. The SSC consists of an eccentric,

lengthening phase of the active muscle that iç followed by a concentricYshortening

contraction. In so doing, the muscle stores elastic energy in the eccentric negative

phase of work, and immediately re-uses this stored energy in the positive

concentric work phase (Enoka, 1994; Komi & Bosco, 1978).

A 60m sprint run is designed to test the body's ability for generating

maximum power and a coordinative effort of speed with efficiency of movernent.

Because the velocity profile for the average subject in a 60m sprint run has the

greatest slope (on a graph plot) for the first 10 metres, which corresponds to the

phase of maximum acceleration, this study was designed to test an initial (1 0m to

20m) acceleration phase and part of the late acceleration / maximum velocity

phases (20m to 60m). These two sprint phases have been designated as

average velocity 1 (VI) for the 10m to 20m distance, and average velocity 2 (V2) for

the 20m to 60m distance of the 60m test sprint run.

Bellotti (1 991 ) considers speed as a complex request made on the body,

which involves different integrated nervous system and muscular components, and

the sprinter's need Io develop (whole-body) speed according to the discipline's

specific requirements in strict adherence to the technical demand of its biological

(neuromuscular - biomechanical) performance model. The necessity for strength

development of the sprinter's leg flexor muscles is stressed, verssus the extensors

as previously pursued. Of the parameters that are most conducive to increasing

limb movement rapidity, Bellotti (1 991) considers exploitation of limb movement

speed via the application of fast and elastic training methods to be of paramount

importance. Such intense and specific training "rnay bring about a distinct

improvement in performance in a number of disciplines." His cursory survey

simply emphasized the need to focus on specific factors that match the parameters s

of his performance model, and no training method was mentioned or eiaborated

1.100 OVERVIEW OF SPRINT TRAINING

There are various training modes (physiological and psychological) that

have been designed to improve certain aspects of a sprinter's performance. Most

of the physiological training modes employ the use of the sprinting legs' stretch-

shortening cycle, although many sprint coaches, perhaps through ignorance, are

f not cognisant of its merits for speed enhancement, and their anatomical knowledge

seerns limited to the narnes of a few muscle groups (Personal obseivations).

Frequency of limb movements, and whole-body velocities attained during sets of

sprint interval training are implicitly implied in these training methods.

1.120 INTERVAL TRAINING

lnterval training (IT) uses the system of set work-outs with repetitive work of a

prescribed intensity and timed recovery periods. It became popular in the early

1950's after Emil Zatopek's popularization of the method by his superior

performances at the Helsinki Olympics in 1952 (Radcliffe & Farentinos, 1985).

This training method uses repetitions of the same distance of the event, with the

l work-out intensity and duration to match that of race pace.

t.130 STRENGTH TRAINING

Strength (dynamic) training with weights have neurologically adapted

axonal size and areas to increase tetanus amplitude, twitch force and conduction

velocity of motor neurons, and muscle torque of 'fast to fatigue' (FF) motor units

(Bompa, 1993; €noka, 1994), as sprinting power is the product of force\irneç speed

of application of th& force (Bompa, 1993; McFarlane, 1993).

1.140 SUPRAMAXIMAL TRAINING

Supramaximal training is an artificial form of increasing a sprinter's body-

speed. This takes place by an attached rope around the waist that pulls the

athlete along a special track at a programmed speed, which is in excess of the

person's maximal horizontal velocity.

1.1 50 SPEED TRAINING

Various training modules stress the different components of an athlete's

sprinting performance. A person leams to run fast by combining al1 the intra-skills

of energised fast, efficient, repetitive leg movements. Speed is a trainable skill

that involves the leamed adaptation of corn plex neuromuscular capability for

precise coordinative limb movernents (Mc Farlane, 1993).

1 .le0 START ACTION TRAINING

According to Delecluse (1 992), even the start action of the acceleration

phase can be improved by training its identifiable sub-components. These are the

athlete's horizontal start velocity of his / her centre of gravity (CG) on leaving the

starting blocks; the start time that is taken to push off from the blocks (disregarding

the reaction time); and the mean horizontal start acceleration that is the quotient of

start velocity with start time (Delecluse, 1992).

1.1 70 ACCELERATION TRAINING

Acceleration training is a form of interval training. It involves leàmed

sequences of very powerful initial leg movements combined with the movernent

skill of overcoming the body's inertia with the legs propelling the centre of mass

wRh increasing velocity. Plasticity of the neuromuscular system forces a leamed

adaptation (of al1 of the above factors) that incorporates all the nuances of intra-skill

acceleration techniques into a unified, comprehensive skill, that manifests the

ultimate in explosively powered limb movements. The training distance varies

between 20m to 30m, and is seldom more than 60m.

1.180 SKlLLS DRILLS

Various dri!ls designed for encoding proper neuromuscular leaming on the

athlete's system have been devised to augment proper biomechanical movements

of the stride action to enhance intra-limb distribution of energy from the centre of

body-mass radially outwards to limbs (Mc Farlane, 1993; Korchemny, 1985).

Plyometrics came into prominence on the world scene during the 1960's

with Veroshanski's (1 969) research, which involved experimenting with different

modes of training. He conceptualized that plyometric training helped to develop

contractile tissue and the entire neuromuscular system for power movements and

claimed improvements especially with speed of muscle contraction. Success in

plyometric training was further influenced by anecdotal results of Valeri Borzov's i

win of 10.0s in the 100m final of the 1972 Olympic Games in Munich, Germany.

Borzov was only 20 years old, and had practised plyornetrics assiduously since

age 14 when his best 1 OOm sprint time was 13s. ..

1.200 SPRINT TRAINING METHODS

Mastery of sprinting skiils is not entirely divorced from the body's functional

adaptations. It requires intersegmental distribution of mechanical energy from

larger to smaller limb segments (Putnam and Kozey, 1989), to maintain appropriate

gait to minimize mechanical energy. The latter is lost as heat frictional energy at

hip, knee and ankle joints. Appropriate foot landing of the &rider's leg also

minimites ground contact time, and maximite ground reaction forces (GRF) of the

drive phase (Bompa, 1993).

1.21 0 FUNCTIONAL ASPECTS OF SPRINT TRAINING

For mastering the functional aspects of sprint training, Korchemny (1985)

used interval training with drills to improve range of limb motion. Running drills

on the spot, and over 50m to 70m, jumping drills on the spot, and over 50m were

utilized to improve endurance (and so rninimize fatigue) of these muscles

contractive forces. Drawn stick figures are represented with indicated movement

patterns that show complete drill sequences (Korchernny, 1985). This is by far

one of the most comprehensive and concise presentations of a sprint training

protocol to be published in recent times. It is rneant for the coach's use, since

concepts such as stretch-shortening cycle's application to the sprinting stride

action, or even eccentric or simultaneous concentric phases of synergist / agonist

and antagonist muscles in tandem are absent. The term plyometrics was

mentioned once without any attempt to explain the myotatic reflex that is the basis

for plyometric power (Chu, 1984; Bompa, 1 993). a

1 220 NATIONAL LEVEL TRAINING

National Sprint Coaches / Master Course (Sprint) Conductors for Athletics

Canada (including Brent McFarlane and the author) have devised different training

strategies to improve athletic sprint performance. Canada's success in sprint

events, was evident at the 1996 Olympic Games in Atlanta, as Canadian Donovan

Bailey's 'golden,' performances in both the men's 1OOm and 4 x lOOm relay events

testified.

1.230 BRENT MC FARLANE'S METHODS

Mc Farlane (1 982, 1993), who has presented topics at many local and

international clinics on speed training for sprints and hurdle events, has

emphasized the use of a number of sets of different types of speed drills specific to

the stride skill in sprinting, and hurdles clearance, to buttress the synchronous

reinforcement of neuromuscular, coordinative leamings for cornplete educability of

the entire neuromuscular system. This consolidated approach ensures repetitive

performance of the properly leamed and programmed skill sequences that

contribute to national excellence of dite athletic performances (Mc Farlane, 1993).

1.240 RESEARCHER'S SPRINT TRAINING METHODS 1.241 SPEED CONSTANCY CONCEPT

This researcher has developed and used two main sprint training modes

from two different rnethodological perspectives. For the speed constancy concept,

the athlete begins a set work-out at a slow speed, and repeats the same distance

exactly every three minutes, using the same combined sense of speed and effort of

the previous run. My research (unpublished data) has shown that both the

athlete's co-joint 'sense of effort - and of speed', maintains an integrated, unified

wholeness and sameness in effort and exertion with each subsequent run of the

set. The athlete builds an increased speed of 3 to 5% per set over the previous

set, for the distance exploited. This can Vary over a 30% to 50% range in intensity

of the athlete's best-tirne performance. A 60 metre set consisting of 30

repetitions, with 3-minute recovery intervals, can be an adequate work out. This

'speed constancy concept' has as yet no known psychological or physiological

basis in the scientific literature. However, athletes' written comments on work-out

sheets over the years, and their sirnilarly paralleled, identical feelings of ease of

training method, and their subsequent performance outcome as top sprinters in

Nova Scotia, may have given some credence to this training mode (Personal

unpublished research).

1.300 STATEMENT OF THE PROBLEM

This research study attempts to determine whether a plyometric method of

rapid knee-raises on experimental subjects could significantly improve their whole-

body movement velocities in a sprint run. The plyometric treatment is the

independent variable, and the sprint velocities the dependent variable.

The piyometric treatment used the dominant dual training stimuli of, 1. a

high frequency of single-leg knee-raises for a short duration, and 2. the stretch-

shortening cycle that is involved in these ballistic rnovements. There are limits to

the complete efficacy of single knee-lift exercises to compensate for the runner's

complete ballistic skill of the stnde action that uses both legs in a propulsive and Y

cyclic, travelling manner. The expectation is, that it would compensate for the

total adaptive training of most of the skills involved in the rapid, rotatory, propulsive

movement of both legs in a sprint run. This performance was compared to a

Control Group that did not use the plyometric rapid knee-lift treatment. ?

1.400 PURPOSE OF THE STUDY

The purpose of this study was to determine whether a plyometric treatment

protocol over a tan-week period, would significantly increase subjects' whole-body

running speeds in a 60 m sprint nin.

1.500 N U L HYPOTHESIS

(1) There will be no significant difference between the Experimental and

Control Groups.

(2) There will be no significant difference among the various testing

sessions.

(3) There will be no significant interaction between the groups and test

eff ects.

1.600 RESEARCH HYPOTHESIS

The plyometric knee-raise exercise protocol on research subjects will have a

significant training effect to increase their stride frequency, and whole-body speed

in a 60 m test sprint run.

CHAPTER 2

REVIEW OF THE LITERATURE

2.000 RATIONALE FOR PLYOMETRIC TRAINING

Plyometrics (a comparatively new field of inquiry of sport science) has been

used as a distinct method for training athletes to maximize their cornpetitive

performance where force in combination with speed is necessary. 'Plyometric

exercises were designed to train a specfic movement pattern, the eccentric-

concentric sequence of muscle activity" (Enoka, 1994). This sequence involves a

change in the ratio of muscle torque to load torque. In an active muscle, when the

muscle torque is greater than load torque, a concentric contraction occurs, but

when the muscle torque is less than the load torque, then an eccentric contraction

takes place. This is the essence of the stretch-shortening cycle (SSC).

In plyometric physioiogy, a rapid muscular - limb movement is based on

reflex contraction of muscle fibres resulting from the rapid loading and stretching of

the fibres (Bompa, 1993). The stretch-shortening cycle potentiates an activated

skeletal muscle to use two different strategies for increasing muscle torque.

2.1 00 ENERGY STORAGE STRATEGIES

A) Mechanical potentiation

The first strategy is the storage of elasticized energy from an eccentric

contraction. Here the actin / myosin cross-bridges are under a time-dependent

elasticized, tensile stress, and use thiç mechanical energy to augment the positive

work of the ensuing concentric contraction (Bompa, 1993; Fung, 1993). The force

exerted by the muscle in the eccentric contraction stores elasticized potential

energy in both the contractile myofilaments and in the structural connective and

cytoskeletal tissues (Enoka, 1994). This nascent energy is available for

irnrnediate re-use, as it has a short half-life, and its force-time curve experiences

rapid exponential decay (Radcliffe and Farentinos, 1986). This is based on the

sliding filament theory of muscular contraction which States that the force exerted

by a muscle is accompanied by the sliding of thick myosin and thin actin filaments

past each other (Enoka, 1994; Bosco et al., 1981 ; Fung, 1993).

In the micro-structure, each myosin filament consists of a heavy meromyosin

head, and a light meromyosin tail. They are arranged in rows in the myofilaments,

and are arranged both in parallel, and serially, so that the myosin heads 'project

laterally from the filament in pairs, at 180 degrees to each other, and at 14.3

nanometer intervals" (Fung, 1993). Thin actin filaments interdigitate these thick

myosin serially, so that when the structure develops tension, the myosin head

rotates (through a 120 degrees angle) to bind with the actin filament to fomi a

cross-bridge. The cross-bridges in this resultant attached state from the acquired

tensile stress (resultant from the eccentric loading), is under a tirne-dependent

contractile strain that would generate a force that is proportional to the

displacement. This bonding reaction of actin-myosin obeyç the laws of first order

kinetics (Fung , 1 993).

B) Reflex potentiation

The second strategy that the SSC uses to enhance muscle torque is the

stretch reflex potentiation (the myotatic reflex) of activated muscle fibres resultant

from the rapid loading and stretching of the fibres (Bompa, 1993). Muscle spindle

ogranelles within skeletal muscle are individually 'wired' and connected to

synapses in the spinal cord. They are sensitive to length changes in muscle, and

sudden muscle lengthening of the myotatic (stretch) reflex that activates these

spindles. Rapid muscle-fibre lengthening causes the intrafusal fibres of the

muscle spindie to stretch, which also stretches the coiled endings of the primary

spindle receptors. Gamma efferent motor neurons that innervate the spindle's

contractile ends stretch the central portion, which activate the primary receptors. A

plyometric motion that suddenly loads the muscle, activates the spindle. This

produces a dynamic response when the primary spindle receptor is activated by a

rapid change in length of the intrafusal fibres coiled around it, and it is this dynarnic

response that implicates the spindle's involvement in detection of rapid stretch that

is incorporated in the myotatic reflex.

When the muscle spindle detects a rapid lengthening of the myofibrils, it

elicits a dynamic response, and a large volley of impulses is transmitted via la

afferent motor neurons of the primary receptor to the spinal cord. There they

synapse directly with the alpha motor neurons, and impulses are sent back to the

skefetal muscle.

This second strategy in the re-use of elasticized energy that the eccentric

elongation contraction potentiates, is simultaneously buttressed with the first.

These combined strategies re-use the rnechanical potentiation of time-bound

cross-bridges, to load the ensuing concentnc contraction with added power for

work (Enoka, 1994).

Plyornetrics is physiologically well suited to work within these complex

neural mechanisms. Plyometric training has been shown to produce significant -.

changes at muscular and neural levols that, in tum, facilitate and enhance the

performance of faster and more powerful movement skill (Bompa, 1993).

The Golgi tendon organ, because it acts as a feedback mechanism to the

muscle spindle, is sensitive to sudden changes in viscoelastic tensile stresses

applied to the muscle. The mechanism allows the efficacy of continuous

monitoring by allostetic feedback, between the muscle's effector structure and the

central nervous system, via the spinal cord (Pearlman and Coliins, 1990). From

this organelle imbedded in the muscle tendon, the stretch reflex generates a

sudden increase of tendon-tensor torque, which causes efferent signals to be

transmitted to the spinal cord. An inhibitory response to the acquired tetanus of

the muscle then occurs. In this manner, too much tension is prevented from

developing in the muscle. This reflex sets an inhibitory response as a protective

mechanism to conserve excessive muscle stretch as potentiated by the muscle

spindle (Bompa, 1993; Pearlman and Collins, 1990).

2.200 NEUROMUSCULAR CONSIDERATIONS

The use of plyometric exercise training seems to develop the reactive

neuromuscular apparatus (Veroshanski and Tatyan, 1983), or the eccentric - concentric activity which loads the contractile components of muscle (Fung, 1993;

Komi, 1984; Bosco et al., 1982). In order to take advantage of the stretch reflex,

the muscle must be stretched with great speed to initiate an increase in the firing

frequency of the muscle spindle (Astrand and Rodahl, 1970). This effect can be

exploited through different forms of plyometrÎcs, whose partial physiological

justification necessitates the need to activate the motor units more rapidly to effect a

better neurological adaptation (Bornpa, 1993).

Force with çpeed of limb rnovernents are necessaty prerequisitesof the

plyometric effect which also involves the stretch-shorten cycle. This (force with

speed), according to Komi (1992). is something more than pure mechanical

quantities, in that its properties activate motor units, initiate cortical and reflex

control of muscle, and also varies with the elastic characteristics of muscle fibres.

Komi (1 992), maintains that the fast stretch of an active muscle causes substantial

reflex potentiation in l a afferent newe fibres from the muscle spindle to the spinal

cord. This causes additional reflex potentiation through many pathways, including

the cortical loop. Also, these reflexes could reach the muscle within about 50 ms

fromtheonsetoftheeccentricstretchphase. Becauseofthiselectromechanical

delay in reflex potentiation, the reflex action may adversely affect the eccentric

phase of the SSC when plyometric motions are perfonned at a large range of

amplitude. However, with a plyometric movement of low-range amplitude, the

myotatic effect may occur during the positive work phase, resulting in a higher

mechanical efficiency which is characterized by a low energy integrated

electrornyographic (IEMG) activity during the ensuing concentric phase (Komi,

1 992).

Muscle fibres form the contractile elements of muscle, and the series elastic

elernents (SEE) form the noncontractile part of muscle. Stretching of the SEE

during an eccentric lengthening contraction produces a time-constrained elastic

potential energy. Recovery of stored elastic potential energy occurs during the

subsequent concentric contraction. This ensuing concentric contraction is

triggered by the myotatic reflex (Chu, 1984, Fung, 1993).

Plyometric training is the physiological concept that the frequency of limb

movement in the striding action of a sprint run, is the key to affecting whole-body

movement velocities (Sale 1987; Komi, 1978), and seems to have neurdogical

validity (Sale, 1987). A plyometric rapid limb movement that mimics only a part of

the striding action in a sprint run has never before been used as a training protocol

to augment faster whole-body speeds. According to Enoka (1 994)' "success in

many athletic endeavours is critically dependent on the athlete's ability to sustain

maximum power productionn.

According to Sale (1987), a bnef intense exercise fosters greater excitatory

neuronal input to recruit large motor units in order to take advantage of limb

muscle strength and contractile speed. All motor anits use faster finng

frequencies in fast contractions as opposed to slow ones. Of the thigh's

hamstrings and quadriceps muscle groups, the latter possess a greater strength

per unit volume of muscle mass than the hamstrings, whereas the former possess

greater contractile strength and higher contraction velocrty (Enoka, 1994). Bompa

(1 993) contends that a faster rate of muscle stretch is more important than the

magnitude of the stretch, that plyometric training is a method of developing

explosive power and that it taxes the dominant anaerobic alactic and anaerobic

lactic energy systems. Bompa advocates the selection of a plyometric exercise

that is specific to the kinetic power of the integrated movement patterns.

A plyometric training protocol is designed to train a specific rnovement

pattern, the eccentric / concentric rnovement pattsm of muscle activity (Enoka,

1994), as well as to facilitate an adaptive response to increase the rate of force

development (Hakkinen et al., 1985)' and maximum tetanic force (Dooley et al.,

1990). The increased rate of force development for immediate utilization of

energy is the essence of the plyometric motion of rapid flexion / extension limb

movements (Bompa, 1993). The stretch - shorten cycle (SSC) has been implicated

as the causal agent of this power potentiated in muscle (Enoka, 1994; Ùbmi and

Bosco, 1978; Radcliffe and Farentinos, 1985).

With any system of athletic training and conditioning, certain drills and work-

out routines are designed to enhance a specific aspect of an athlete's performance

(Radcliffe and Farentinos, 1985; Bompa, 1993). These factors seem to suggest

that a plvometric exercise protocol of rapid knee raises could perhaps increase the

speed-conditioning of the largest muscle groups in the human body to positively

affect sprinting velocities.

2.300 TRAINING TECHNIQUES FOR THE STRETCH-SHORTENING

CYCLE

ARhough differenr kinds of plyometric training techniques have been devised

to enhance limb torque movernent patterns peculiar to many sports and activities

(Bompa, 1993), there is no available study that deals exclusively with a single-leg

exercise protocol such as knee-lifts as the independent variable, to positively affect

wholebody velocities in sprint running.

A nurnber of researchers (Thys et al., 1972; Asmussen and Bonde-Petersen

1974a, 1974b; Komi and Bosco, 1978; Komi, Bosco et al., 1981, 1982) have

investigated various aspects of the stretch-shortening cycle. They have

conducted experiments to test the gain in work perfomed by a concentric

contraction with and without a prior eccentric contraction. In a few cases, delayed

tirne-intervals (of the coupling stage) between flexion and extension, caused the

leg extensors to relax. This allowed a transformation of potential energy

expenditure into heat energy at the negative work phase. In effect, CO-joint,

mechanical-reflex potentiation was allowed to be lost without adding to the work :

efficiency of the concentric phase.

19

2.400 THYS ET AL., (1972). "UTILIZATION OF MUSCLE ELASTICITY

IN EXERCISE"

A study by Thys et al., (1972) entitled "Utilization of muscle elasticity in

exercise" used three subjects for deep-knee bend exercises with a pause, and

three subjects without a pause between leg flexions and extensions. Each group

performed deep knee-bending from an upright position for a 1.5 second interval, at

a frequency of 20 cycles / minute. The exercise lasted for six minutes for each

group. In one group the knee Rexor continued with a rebound and no pause

between the leg flexion and extension. In the other group there was a pause

between the negative work of knee flexion and the positive work of knee extension,

the degree of knee flexion being constant for both conditions.

The mechanical work was measured by having subjects exercise on a force

platform that was sensitive to vertical forces. Strain guages on the force platform

sensitive to displacement of the centre of gravity (CG) and vertical speed of the CG

were utilized. These guages ignored horizontal accelerations of the CG, intemal

work caused by viscosity of body tissues, and muscular contractions that did not

lead to displacement of CG of body-mass. For electromyographic (EMG)

recordings, surface electrodes at the quadriceps sural level insured that leg

extensor muscles were relaxed between flexion and extension movements.

Results indicated that in the rebound movements, the greater speed of lifting

was due to two contributing factors, the speed of muscle shortening of both the

contractile elements, and the series elastic elements. These myofilaments were

stretched during the quadriceps eccentric contraction of the negative work phase.

In the 'no rebound' exercises, slower lifting speeds were experieked since

the loads on the muscles limited their shortening velocities. The contractile

elements contrîbuted to the muscles in shortening, whereas developed tension

occurred in elongating the series elastic elements.

Concomitant to the increase in average power of the rebound group that

resulted from the increased speed of the entire muscle shortening from the body lift.

was the lower energy expendlure, and the greater mechanical efficiency of

movement.

Mechanical efficiency based on the mechanical work performed in the lifting

phase was due not only to the contractile elements of the active muscle, but to the

additional energy potentiated by elastic energy stored in the stiffness of active

elongated muscles during the negative work phase.

The difference in the rebound and no rebound exercises supported this

study's hypothesis that elastic energy stored in the stretch of an active muscle

during the negative work phase accounts for part of the work done by muscles. In

some exercises, provided that the positive work immediately follows the negative

work as the muscle relaxes, the elastic energy is converted into heat.

2.410 ASMUSSEN AND BONDE-PETERSEN, (1 974a). 'STORAGE OF

ELASTIC ENERGY 1N SKELETAL MUSCLES IN MAN"

Nineteen male and fernale subjects performed three different kinds of jumps

to test whether mechanical energy in the fomi of elastic energy, can be absorbed

anu temporarily stored in active muscles. They compared the release of extemal

rnechanical energy from activated muscles with and without previous stretching,

using three different exercise protocols. The three different types of vertical jump

exercises used were, the squat jump (SJ), the counter movement j u rnpY(c~~) and

the drop jump (DJ) from different heights. Results indicated statistically significant

differences (p < 0.02 level) in energy levels of the three jump types.

In the SJ subjects were assumed to have exerted themselves maximally

from the start of the jump. For the CMJ, when a counter movement was performed

before the jump, energy stored in the body was in excess of that used for muscular

contraction. Some of the unused energy degenerated into heat, however some

was absorbed by the series elastic components of the myofibriis. This latter store

potentiated the mechanical energy of the positive work phase, and the increase ir.

energy was 23% greater than that for the notmalized squat jump condition.

For the drop jumps heights of 23 centimetres (cm), 40cm and 69cm, more

energy was available for the elongation eccentric contraction that stretched the

elastic components. This energy corresponded to the maximum tension that the

muscles contractile mechanism voluntarily produced. Concomitant increase of

tension was produced temporarily by the acceleration of gravity acting on the

viscoelastic and elastic components. The increase in negative energy

corresponded to increases in height of the DJ, except that values decreased for

the 69cm jurnps because of the subjectç' possible fear of over-sxertinç or hurüng

themselves frorn the higher position.

The storage and release of large amounts of elastic energy necessitate

structures t hat cou Id absorb, contain and release these large arnounts of energy.

Resting muscles were dismissed from suspicion of storing appreciable amounts of

elastic energy because of their very low stiffness in their physiological range of

movement. However, because active muscles have a greater degree of stiffness

in the same range, the soleus and vastus lateralis displayed higher €MG readings.

In these DJ conditions from heights of 40cm and less to the force platfok,

touchdown was preceded by an increase in €MG activity from the soleus. This

was due to the anticipated increase in muscle activity that started about 100ms

before touchdown at the force platform.

The period of the negative phase during which time the storage of elastic

energy occurred was 268ms for the CMJ, and 190ms, l62ms and 141 ms for drop

jumps from heights of 23cm, 40cm and 69cm respectively.

The increase in negative energy normalized from the SJ condition of zero,

the CMJ showed a 22.9% increase, and the drop jumps an increase of 13.2%,

10.5% and 3.3% for heights of 23cm, 40cm and 69cm.

2.420 ASMUSSEN AND BONDE-FLEMMING, (197413). 'APPARENT

EFFICIENCY AND STORAGE OF ELASTIC ENERGY IN HUMAN

MUSCLES DURING EXERCISEn

This study measured the apparent eficiencies of three subjects during

loaded ninning on a treadmill at a constant velocity of 10 krnfhr (2.78 rn/sec) with

attached known weights suspended over a pulley. These efficiencies of loaded

running using different weighted resistances to retard horizontal velocity, were

compared against their nomalized running efficiencies at a constsnt velocity of

2.78 m/sec.

One of the three subjects was tested for apparent efficiencies of load-

walking against norrna! walking, both at constant horizontal velocity; and for load-

bicycling against normal bicycling, at constant peddling velocity. This subject

was also tested for apparent efficiency of deep knee-bending with and without

rebound; and half knee-bending with and without rebound.

The resulting efficiencies for the increased effort to normalize a sieady-state

work Pace were measured. The resulting efficiencies for the different loading

modes of resistance exercises, compared to normal running, walking and bicycling;

and those of knee-flexions with and without rebound, gave a measure of the

elastic energies. These energies of the various resistance loading modes were

potentiated in eccentric elongation contraction of leg extensor vastus lateralis

muscle. These energies were reutilized. Their comparative efficiencies of

metabolic work rate of the stressed, compared to nomalized exercise modes,

measured the storage of elasticity in the active muscles during exercise.

This study is similar to an earlier study (1974a) by the same authors as it

deals with exercise that implanted mechanical energy that was stored as elastic

potential energy in the series elastic components of leg extensor muscles. This

energy was available for reuse during the subsequent contraction, during different

jump modes in man. However, this later study is different in that it deals with

comparative efficiencies of energy utilization on leg extensor muscles that were

forced ta work harder during different loaded regimes.

For the constant velocity treadrnill running, a string attached from the subject

passed over a pulley with a constant weight suspended, defined the constant

horizontal resistance that the subject had to overcome to maintain the constant

velocity of 2.78 rn/s. This known weighted resistance was equivalent to the extra

effort (the increased change of effort) that the subjects had to overcome to

maintain a constant speed. The proportional increases of effort to rnaintain

metabolic homeostasis of a load for a 7 to 8 minute period reflected an aerobic

ventilatory response that was equivalent to the load power (dernand) weight on the

subject, and solicited the periodic increases in load power. This in tum, elicited an .. equivalent ventilatory response in subjects as positive work power.

lncreases of work load on the subjects' shoulders reflected the concomitant

increase in work power of the horizontal retardation effect to maintain the 2.78 mls

horizontal body-speed. It was found that the increase in load power equalled the

product of cornbined body weight and shoulder load with velocity of subject's

centre 05 mass.

Results of the increases in apparent efficiencies for the various exercises

were: load running to normal running 53.8%, 37.6% and 41.2% for the three

subjects; and for the one subject, 53.8% for load / normal running; 32.3% of load /

normal walking; 25.1 % for load / normal bicycling; 41% for deep knee bending with

rebound, and 26.1 % without rebound; 41% for half knee bending with rebound and

21.9% without rebound. For bicycling and the knee extensions without rebound,

al1 of the negative work of the eccentric phase degenerated into heat energy.

During running, 35% to 53% of the energy absorbed in the negative phase

by the series elastic element of the vastus lateralis' leg muscles, were re-used as

mechanical energy for positive work power. The corresponding values for walking

and the knee extensions with rebound were 23% and 34% respectively.

In running, the mechanical activity of the leg extensor muscles performed

altemate negative and positive work during ground contact period. During the

latter part of tha flight phase, the eccentric elongation of the leg extensor muscles

performed negative work. At the ground contact penod, the potentiated elastic

energy was stored in the muscles myofibrils' series elastic elements from the

previaus eccentric phase. This energy was immediately unloaded ont0 the leg

extensor muscles contracting concentrically, wlh the additional rebound energy to

aid subject's backward leg-drive for foward whole-body movement. The low

values for bicycling reflected the leg extensor muscles relaxation during the up

stroke, and did not potentiate extra energy to unload to the resultant down stroke.

In the present experiments, the subjects ran at a strïde frequency of 180

strides per minute (3 strides / second), and a stride period of 333ms. Ground

contact time was 80% of the 333rns. This gave a foot implantation ground phase

of 260ms, and about half of this was spent doing negative work. The twitch time of

the average calf muscle to peak is 74ms. so there was sufficient time for the active

motor units in the negative phase of work to store elastic energy, and to carry it over

into the subsequent period of the positive work phase without any extm metabolic

CO&.

During the negative phase of the running movements, the energy that was

implanted in the muscles was partly gravitational potential energy, and partly

kinetic energy. Also, during loaded running, perhaps only that portion of the

implanted energy involved the subject's centre of gravity (CG) was assumed to

help in maintaining the extra load. In the present experiment, the work done on

the limbs was the same as in unloaded running that maintained the same stride

frequency; whereas, the work done on the CG is the algebraic sum of the vertical l i f t

component, together with the numerical vector for the horizontal accelerations of

the CG. Since these two are in phase during running (as opposed to walking),

they can be sumrnated algebraically. As a consequence, this avails the same

magnitude of negative work power for reuse in the positive stage of running, as in

the case for loaded running. The total work done on the CG equals work done on

vertical lifî of the CG, plus work done on horizontal accelerations of the CG.

Results for the rebounding experiments support those for loaded running, in

that, when rebound was possible, the efiiciency of 40% is higher than with no ?

rebound's 24%. The value of 3 kcaVmin of positive work for the rebound after

negative work gave 1 .O2 kcaVmin without the extra metabolic cost, also implies

26

that after elastlc recoil, the 3 kcaVmin of negative work will be degraded as 1 .O2

kcaVmin positive work. This represented 34% of the negative work perfotmed.

With the half knee-bending exercises, 51% of negative work performed at rebound

was reused in the subsequent positive work phase.

The cross-bridges between the filaments and in the series elastic

component of the active vastus lateralis leg extensor muscle, are the suspected

t causative factors as sites for storage and reuse of mechanical energy for added

leg power, in the loaded and normal running, and in the knee flexions with

rebounds.

2.430 BOSCO AND KOMI, (1979). 'POTENTIATION OF THE

MECHANICAL BEHAVWR OF THE HUMAN SKELETAL

MUSCLE THROUGH PRESTRETCHING"

This work investiçated additional mechanical energy potentiated in leg

extensor muscles through drop jlimps (DJ) and counter movement jumps (CMJ) as

the experimental group, compared to static jump (SJ) subjects used as the control

group.

In a vertical jump that involved movernents around severai joints, force- 7

velocity and power-velocity curves were denved from the vertical ground reaction

forces (GRF) and knee angular velocities (KAV). For the vertical jumps,

prestretching of the leg extensor muscles preceded their shortening through CMJ

or DJ from various heights ont0 a force platform. The performance of skeletal

muscles increased through prestretching, was attributed to the co-joint effect of t

stored elastic energy utilization, and reflex potentiation of muscle activation.

lncreases in force velocity, and power velocity cuives were obtained from a

27year old male subject who executed the CMJ from an erect position; DJ from

different heights to activate the leg extensor muscles, and 8 SJ with loads of 10, 20,

40, 60, 80, 100, 1 10, and 160 kilograms (kg) on the shoulder. An 85-degree

knee-flexion angle was constant for each of the thme jump types, and the CMJ did

not use the greatest (160 kg) load of the set. This subject drop-jurnped onto a

jump platform from heights of 20,40, 60, 80, and 100 centimetres (cm) with no

loading on the shoulders using two different protocols.

The first condition involved vartical jumps immediately after touchdown on

the platforni, with a smail change in the knee angle during ground contact. For the

second exercise protocol, the subject dampened the gravitational force longer with

the greater change in knee angle. In both the CMJ and DJ conditions, the

shortening of the active leg extensor muscles was preceded by prestretching of the

muscles. Results indicated that the prestretching increased both the GRF and the

calculated mechanical power by positively rnodifying both the force-velocity and

power-velocity CU mes.

Kinematic measures included angular velocity and amplitude of movernent

around knee joints, calibrated for zero degree in the standing position, and

maximum speed of knee-extension. Results indicated a greater knee-angular

force-velocity for the CMJ as compared with the SJ (the force velocity being always

higher in the CMJ than in the SJ for any given load).

Power velocity curves for the DJ with undampened condition at touchdown

was higher than the corresponding dampened condition, and for the SJ. The

quadriceps Ieg extensor muscle group was implicated as the dominant muscle 1

group from which force and velocity calculations were made. It was assurned that

the GRF force-time cuwe was côused by the quadriceps muscle group forces, and

the angular velocity of the knee joint was caused by the quadriceps linear velocity

of shortening.

Results indicated that the increase in the CMJ's force velocity cuwe reflects

the storage of potentiated elastic energy, that was subsequently used by the leg

extensor muscles. The restitution of elastic energy during the drop jump

conditions from vertical heights, reflected the storage of elasticized energy that was

reused by the leg extensor muscles.

The activated quadriceps leg extensor muscles stored a substantial amount

of potential energy when it was forcibly stretched in the DJ, and CMJ conditions,

and part of this energy was recovered during the positive concentric work phase

with a short time delay within the stretch-shortening cycle. This muscle group was

activated before touchdown, and before the eccentric contraction negative work

phase in the CMJ's, where the early activation exceeded the quadriceps' average

electromechanical delay of 50 ms that prepared it to resist the 9.81 d s / s

gravitational force acting downward on the quads.

Storage of elastic energy during the eccentric stretch phase was long

enough to elicit a stretch potentiation via the la afferent alpha motor neuron

impulses to the spinal cord.

Because of basic muscle spindle functions, the length-sensitive secondary

afferents were activated during a starting position of the SJ; whereas, with the CMJ

of DJ, the primary afferents were responsible for the reflex potentiation of the

activity.

Short range muscle stiffness (SRMS) of the quadriceps was the suggested ?

possible cause for the differences of the dampened and undampened DJ

conditions, for force velocity and power velocity curves. This SRMS reflected the

combined (actin 1 myosin) cross-bridge stiffness of the elasticized locked

microfilaments under tensile stress at touch down times. This SRMS disappeared

when damping was allowed in the drop jumps, as mechanical delay of tension in

the viscoelastic muscle durhg hysteresis, lost its potentiated elasticized energy as

dissipated heat. This darnping effect seemed to have exceeded the 15 ms

coupling tirne of extensor to flexor torque in the delayed jump rnovement, and this

was associated with loss of elasticized energy in the muscles' myofilaments, and

caused a decrease in perfomance in the dampened SJ.

The increase in performance of the undampened SJ, and CMJ were

attributed to the utilization of stored elastic energy of the SSC, and to the stretch

reflex potentiation of quadriceps leg extensor muscle activation during these

exercise regimes.

2.440 BOSCO, KOMl AND ITO, (1981). "PRESTRETCH POTENTlATlON

OF HUMAN SKELETAL MUSCLE DURING BALLISTIC MOVEMENTS"

This 1981 study examined aspects of the stretch-shorten cycle (SSC) in

which the condition of the active muscle before, and during the transition from the

prestretch eccentric phase, to the shottening concentric phase greatly influenced

the final performance of muscle. Fourteen dite male power athletes did vertical

jumps on a force platforrn, with and without a prelirninary counter-movement. For

the counter-movernent jumps (CMJ), amplitude of the bent knee, velocity of

prestretch muscle elongation, and end-torque force were dependent variable

parameters of the study. t

Frorn the angular displacement and reaction force cuives, the coupling time

that indicated the transition from the end of prestretch eccentric phase to the

beginning of the concentric phase was reduced. Mechanical performance

parameters for the CMJ were compared with and without counter-movement, and

results indicated that average concentric force was enhanced 66% (423N), and

average mechanical power bÿ 81% (1 158 watts). The potentiation effect of the

study .rades jointly and directly with prestretch force, prestretch speed and short

coupling time of 23 ms.

Results also indicated that changes in the prestretch condition of the

eccentric phase modified the actin / myosin cross-bridge integrity, because of joint

association of storage and imrnediate reuse of elastic mechanical energy. The

latter is associated with high velocity of prestretch muscle elongation, high

eccentric torque, and short coupling time. Reflex potentiation is also irnplicated

primarily with mechanical potentiation in the joint contribution to the enhanced

performance.

Comparison of performance variables of SJ and CMJ showed the latter to be

superior. Use of the SSC for the CMJ enhances muscle performance over pure

concentric contribution to the SJ. Average force and power output for the CMJ of

66% and 81 % over that of the SJ is attributed to the speed of the deceleration

phase. Other influential factors include the concept of short range stiffness that is

related to the coupling time between eccentric and concentric phases.

In the concentric phase, a fast stretch with small knee amplitude caused the

final eccentric force to be high. This in tum promoted induced stress that made

transition from eccentric to concentric phase to occur more quickly. The negative

correlation between end of stretch force and coupling time, supports the above

hypothesis. For the short coupling time, the average period for cross-bridge

attachment is 15ms. At this time the meromyosin heads of the filaments are rotated

120 degrees backward in a cocked position, strained against their natural 'relaxed'

position (in resting muscle) to a position of higher potential energy (in active

muscle). The lengthened cross-bridges can become detached with an elongated

stretch, or with an elongated coupling time, and for large amplitude eccentric

stretch where sarcomere slipping may occur.

The potentiation effect of this study was mainly of mechanical origin, being

associated with the attachment-detachment cycle of actin-myosin cross-bridges.

Also, the fast stretch of an active muscle causes significant stretch reflex

potentiation via l a afferents from the muscle spindle to the spinal intemeurons.

Jointly with increased motor neuron activity, the reflex potentiation to the muscles

while contracting, would make the cumulative force quite large at the end of the

eccentric phase.

This increase of force causes muscle stiffness to increase and accurnulated

stress, as stiffness, favours a short coupling time in the SSC. Stretching the active

muscle can also cause reflex potentiation via the cortical loop. Neive impulse

transmission can access the muscle within 50 ms from the beginning of a stretch.

And because this 50 rns corresponds to the end of eccentric impact in sprinting,

there is possible contribution to stretch reflex potentiation.

Both elastic and reflex potentiations have contributed to enhanced muscle

performance, although this study was not intended to investigate reflex

potentiation. Because the work and force velocity curves shifted to the right in this

study, the elastic phenomenon was the main causative parameter, although reflex

potentiation also contributed to power fast movements. ?

2.450 BOSCO, KOMl AND ITO, (1982). "COMBINED EFFECT OF

ELASTIC ENERGY AND MYOELECTRICAL POTENTIATION

DURING STRETCH -SHORTENING CYCLE EXERCISE"

In this 1982 study, vertical jumps were camed out on force platforms with

and without benefit of preliminary counter movements. These exercises tested leg

extensor vasti lateralis and medialis muscles' increases in myoelectncal activity for

enhancement of elastic energy potentiation in the stretch shorten-cycle.

This study attempted to clanfy the possibility for restitution of elastic energy

and the influence of stretch reflex in many stretch-shortening exercises. In this

manner, the mechanical potentiation effect of stretched active thigh muscles in the

positive, concentric work phase was examined. Three experienced athletes in

their mid- twenties did three types of jumps on force platfoms, static jumps (SJ),

and counter-movement jumps (CMJ) and drop jumps (DJ).

The SJ were performed with shoulder loads that ranged from 15 to 220% of

body-weight, with preset knee angle at 90 degrees, and with the CMJ, subjects

started from erect standing and executed to downward counter-rnovement at the

same 90 degree knee-flexure as in the SJ. For the DJ, subjects used different

stretch loads on activated leg extensor muscles to land on a force plafform from

heights of 20,40,60,80 and 100 cm. The force platforni measured maximum

isometric force at al1 joints with zero angular velocity, and an electrogoniometer

rneasured angular velocity and amplitude of movement about the knee joint, and

maximum speed of knee extension.

In an effort to study neuronal influence in this stretch-shortening exercise, m

miniaturized skin electrodes were used on vastus lateralis, vastus medialis and

rectus fernoris muscles that were fixed to bellies of the muscles. The

electromyographic (EMG) calculations were made for the eccentnc and concentric . phases of each jump in a separate rnanner.

Graphed results indicated that the force velocity curve was displaced to the

right for the concentric phase for jumps that were performed with either drop jump

(DJ), or preliminary counter-movement (CMJ). For the squat jump (SJ) with no

extra load on subjects' shoulders, the knee angular velocity of 486 Newtons (N) to

give a force increase of 40.7%.

The graphed curve for power-velocity was also right-shifted, with 1240 to

1174 watts (43%) respective increases in mechanical power. The mechanical

potentiation of power-velocity and force-velocity curves for the three subjects were

similar.

lntegrated electromyographic (IEMG) activity on vastus lateralis and vastus

medialis muscles reflected the average force of positive and negative work phases

of the three jumping conditions. Electromyographic activity increased linearly with

stretching speed of DJ and CMJ when treated together.

In the CMJ and DJ, performances in which the stretch-shortening cycles

were used gave higher results than those of the SJ that did not beneffi frorn the

SSC, but relied wholly on the shortening type of concentric contraction. As a

result, force-velocity curves were shifted to the right for the CMJ and DJ exercise

regimes. Minor intra-individual differences highlighted potentiation of the positive

phase of the CMJ to be caused mainly by an increase of the IEMG activity, because

of an increase in motor unit activation in the CMJ when cornpared to SJ; whereas

the other two subjects showed no differences in IEMG activity between SJ and '.

CMJ. The increase in performance in the positive phase of the CMJ was

explained to be due mainly to the effectiveness of the recoil of elastic potential

34 i

energy in the muscle during the eccentric stretching phase of the SSC.

The small difference between CMJ and SJ values, (Bosco et al., claimed),

may have been due to the small contribution of the elasticity in potentiating

performance of the CMJ in the positive work phase. An elongated coupling time

of 500ms is the attributed causal agent for CMJ executed with heavy loads that

emphasized an elongated stretching phase, and delayed the transition period

between the eccentric elongation phase, and concentric contracted phase.

Because of this elongated period, the pent-up tension of stored elastic energy lost

its stressed mechanical potency; but with lower loads and shorter coupling times,

conserved the potency for re-utilization of stored elastic energy.

The substantially better result of the DJ's positive work phase was explained

I from mechanical and electromyographic view points, in which the negative phase

of the DJ was charactenzed with a very large force that increased with those of

dropping heights. This in tum was related to increases of averaged stretch-

shortening velocities of the vasti muscles.

Because of very high IEMG activity that was even greater than the maximum

recorded for SJ conditions, enhanced neural potentiation was the suspected

causative factor. This occurred either via spinal or cortical reflexes. Increased

force that leads to muscle stiffness is increased because of increased force of

eccentric contraction that should facilitate conditions for excellent potentiation of

muscuiar performance in the ensuing concentric phase.

When the IEMG activity is plotted on the same graph, the inhibitory reflexes

of the Golgi tendon organ surpassed the facilitated potentiating effects of the vasti I

muscle spindles. High IEMG activity in the eccentric work phase of thé leg

extensor muscles was not accornpanied by concomitant greater force values, and it

was speculated that a jointly high lEMG with low average force in the CMJ's

eccentric phase characterized a certain pattern of motor unit activation. A further

speculation noted that a shift in motor un l recruitment from joint phasic with tonic,

to singularly phasic units that occurred only during ballistic motion, could not be

substantiated from the present study. Also, command signals with motor unit

behaviour for smooth ramp and ballistic type of motions may differ, in that the two

types of movements are controlled frorn different parts of the brain.

Because the quadriceps femoris was the greatest contributor during the

phase of movement from which the force-velocity and power-velocity curves were

made. EMG recordings were Iimited to vastus lateralis, vastus medialis and rectus

femoris muscles.

The counter-rnovement superimposed on the SJ, tumed it into a CMJ, and

established a base from which the SSC's involvement in the latter and manifest as

CMJ, reinforced the difference in their force, power and coupling time parameters.

Both SJ and CMJ employed similar movement amplitudes around the knee

joint in the concentric phase. Joint variations expressed as correlation factors

revealed many mechanical parameters' correlations with the 'potentiation'

variables of force (F) and power (w) changes. Changes of force correlated \

positively with prestretch speed (r = 0.53)' and positively with instantaneous force

at end of prestretch phase (r = 0.51). Force also varied negatively and inversely

with coupling time (r = -0.35), and coupling time was positively conelated with

movement amplitude: the greater the movement amplitude, the longer the coupling

time. Coupiing time is the length of the 'isometric' period at end of prestretch ?

eccentric phase, and beginning of the concentric shortening phase.

36

2.500 GENERAL OBSERVATIONS

The hypothesis that a forcibly stretched muscle is able to store rnechanical

elasticized energy in the myofibrils' series elastic components in the eccentnc

phase of the stretch-shortening cycle, while doing negative work, to reuse this

nascent mechanical energy to potentiate the shortening contraction phase of

positive work, has been borne out in the previous studies.

There has been an evolutionary growth in complexity of factors that

potentiate a rapidly stretched muscle from Thys et al., (1 972) study of rebound

exercises with a pause, and without a pause. The latter, impiicated the series

elastic components elasticized state for temporarily consenring this energy for

reuse. Asmussen and Bonde-Petersen (1 974a) investigated implanted

mechanical energy stored as elastic potential energy in the series elastic

components of leg extensor muscles. This energy was available for instant reuse

during the subsequent concentric contraction. Their further study (1 974b), tested

the extent to which mechanical energy was potentiated, using different loads in

counter movement jumps. The necessity of a short coupling time between

eccentric and concentric phases was also suggested as contributing to the

potentiation effect.

Later, studies by Bosco, Komi and Ito (1981), of the potentiation effect (PE),

found that this PE varied jointly and directly with pre-stretched force, prestretch

speed and short coupling time. Cornparison of performance variables of SJ and

SMJ exercises found the CMJ to be superÎor. The concept of short range stiffness

due to increase force of stretched muscle under temporary stress, contributed to a

shorter coupling time that cumulatively potentiated mechanical efficiency of the

SSC. Reflex potentiation of the stretch reflex caused by increased motor neuron

37

activity between muscle spindle and spinal cord, increased the potentiation effect

of the series elastic components. These researchers' ensuing (1 982) study

designed to investigate myoelectrical potentiation of DJ'ç and SMJ's, found that

CMJ executed with heavy loads increased coupling times to 500 ms, and so

lowered the potentiation effect. High IEMG activity in the eccentric work phase of

the leg extensors increased performance parameters of this vasti group of muscles.

CHAPTER 3

METHODS AND PROCEDURES

3.000 SELECTION OF SUBJECTS

Notice board requests soliciting volunteer subjects for the 10 - week study

were posted at various sports stores and sports facilities in the Halifax - Dartmouth

metro area. Of the forty-two subjects who initially signed up for participation, only

thirty attended the first meeting. At this 'familiarization' meeting, the methods,

procedures and reasons for the study were explained to the subjects. All

questions were answered and a 'PAR Q' questionnaire fom was completed and

signed by the subjects. This fomi identified their health status and suitability for

engagement in the exercise program. A consent fom that included a Waiver of

Liability Statement from Accidental Injury' was also signed. The Graduate Ethics

Cornmittee of Dalhousie University gave written consent to carry out this research

project using human subjects. By random selection, 15 subjects were assigned to

the Experirnental Group, and 15 to the Control Group (Tables la and Ib).

3.1 00 LENGTH OF STUDY

The study was conducted over a ten-week period. Subjects met between 5

and 7 pm, three tirnes a week on altemate d~ys. The sessions lasted for forty

minutes for both groups, and 1 hour: 10 minutes for the Experimental Group when

doing the treatment. A Pre-Test run was conducted at the beginning of the study

for both groups af&er the general warm up session, and Post-Test nins were

perfonned at two-week intervals. Both groups experienced identical warm up, and

Table 1 a: Anthropometric data for Experimental Subjects

Table 1 b: Anthropometric data for Controi Subjects

L

Ethnic Status Caucasian Caucasian Caucasian East lndian Caucasian

Subject

1

2

Ethnic Status Caucasian Caucasian Caucasian Caucasian

Averaaes 1.75 75.4 36

Athletic Status

Marathon Runner Jogger

Sex (MF) M

Subject

1

Triathlete Jogger Non-athlete

Height (m)

1.78 1.69

Height (ml

1.89

Mass (kg)

78.1

Sex (M/F) M M

Pulse (MidMax) .38/152

2 3 4

Age (yrs)

27

Mass (kg)

72.6 64.9

-Pulse (MiniMax) 5311 80 641145

M M M M

3 4

Athletic Status

Triathlete 1.55 1 -68 1.89

Age (Y=)

37 31

77.6 63.6

5711 90 41155 4013 40 5611 62

1.82 1.75,

79.0 66.3 78.1

42 55

53170 61 1162 5811 55

40 41

5 Averages

Jogger Non-athlete Aerobics

33 34 51

M F M

1.78 1 -76

74.9 70.7

39

test run protocols, except that the Experirnental Group did the plyometric knee-lift

treatment after every w a n up session, three times a week for ten weeks.

3.200 ATTRITION OF SUBJECTS

Of the 30 subjects who started the study, only 10 in the Experirnental Group,

and 6 in the Control Group completed the study. Because of discontinuity of

attendance and non-continuous information, only three sets of test run results were

used, those of the Pre-Test and those of Post-Tests 1 and 2. To compute

continuous results, only 5 subjects were selected from the Experirnental Group,

and 4 from the Control Group.

3.300 TESTING SESSIONS

Beginning at the Orn mark, al1 subjects had to sprint through the 60m

distance at their maximum velocity. This 60m sprint test run distance was split into

three sections, Om to 10m; 1 Orn to 20m (VI); and 20m to 60m (V2) . Split times for

each subject were electronically obtained for the V I and V2 contiguous segments.

The maximum acceleration phase from the Orn start to the 10rn mark, was not

recorded.

For each subject, average velocity data was collected for two phases of their

60m test run: average velocity (VI) for the 10 to 20m distance, and average

velocity (V2) for the 20 to 60m distance. Their weighted, averaged, combined

average velocities for this 50m distance were used in the matrix of results.

(Appendix A). After an initial Pre-Test run, 5 Post-Test nins were performed at two 9

: week intervals.

Each session consisted of a half-hour warm up for both groups. During this

time there was complete mixing of subjects. Afterwards, only the Experimental

Group did the high knee-lift treatment. The test runs followed the warm-up period,

on test-run days. On these days, the plyometric treatment followed the test runs.

3.400 TESTING PROCEDURE

The 10 week research period was composed of a conditioning session for

the first week, and 3 microcycle periods, each of a 3-week duration. The original 1

plan was to begin the plyometrics with a 5-second set for each kg. However,

during the first session, very few individuals could maintain the fast CO-ordination of

the rapid, ballistic movements, for more than 3 seconds. Since the CO-ordination

skill was an integral part of the acquired rapidity of limb movement or speed skill, it

was necessary to begin with a more cornfortable intensity.

3.500 PHYSICAL SET - UP OF RESEARCH AREA

The Dalplex indoor track (Appendix C) with a rubberized, resilient and

compliant surface was the venue for the entire 10-week research period. The

60m test run distance was rneasured along the most-straight throughway of the

oval track-concourse, such that the last 30rn distance extended along a straight

I path. This oval concourse consists of 120 degree-angular tums. Distance

intervals that comprised the 60m test run distance of the track, were measured by

the experimenter (with Mc Gill University Engineering Field Survey School and

field geological experiences), and an electronics technician, using a steel metric

tape. At regular 10m intervals, distances were offset at 90 degrees from direction w

of transit, and projected to the inner sill of track, and elevated to, and marked on the

Appmd'i D: A Typicd Monitoring Station with a BeamCoupled Transnitter-ReceÏver Unked to a Digital Eecironic Uock Timar (SomBWhat Schematic and Not to Scale)

Eiectronic timing devices were installed across three sites of the 60 m

distance, at 1 1 Ocrn height-levels across the IOm, Zorn, and 60m intewals of the test

run area of the track. Each of the three transmitten emitted a horizontal, intense,

narrow-ban electronic beam that was picked up by a receiver across a marked line

of the track. Two digital electronic clocks with a precision of (plus / minus) 10ms

recorded broken beams (when subject sprinted from Om through the 60 m mark) at

the 1 Om, 20m, and 60m intewals (Appendix D). In this rnanner, two sprint times for

each distance between 10m and 20m; and 20m and 60m were recorded on an

electronic timer (Appendix A). The Om mark was also cleariy indicated with yellow

markers at floor Ievel; and red markers at chest height levels on the adjacent wall.

This colour marking scheme was unifomly repeated at each of the Om, 10m, 20m,

and 60m track interval, and aided the counting of a subject's stride for the 50m

portion of the 60m test run.

In this manner, accurate transit records were captured on the two digital

timers for (the 50m distance composed of) each of the two contiguous, continuous

test sprint run distances of 10rn and 40m respectively. Each of the two average

velocities, VI. and V2, was obtained by dividing each sprint distance by time taken.

The weighted average of the two average velocities, weighted for (1 0-20m & 20-

60m) distances, were recorded. Readings were collapsed onto the matnx of

Table 2.

Both timed distances and stride countings were collected from between the

10m and 60m marks, only. There were no time or stnde readings from the Om to

10m station for any of the results.

When a subject accelerated through the 10m mark, he / she broie the

electronic beam that the transrnitter emitted to the receiver that was set up on

Figure 2. Graphed Results of Plyometric Knee Uft Frequency CorreIated with Stride Frequency for Three Tests

O 1 2 3 4 5

Knee Lift Frequency

.' Pre-Test Run

1.99 2.28 1.82 1.75 1.76

L

Post Test1 2.12 232 2-05 1.86

Microcycle 1 2 3

Post-Test 2 2.16 2-35 2.04 ,

1.74

lffiee Lift Frequer 3.5 3.8 3.8

1-61 1 1 -60 41 3.0 5 ( 4.3

Table: 2a. Absolute difference of Pre-Test's average velocity with combined average velocities for Post-Tests 1 and 2 of EXPER1MENTA.L GROUP.

1 Post-Test 2 1

Absolute Increase = [6.3624 - 6.76341 = (0.4010)

Percentage Difference = (0.4010 x 100)f 6.3624 = 6.30 % = Increase in cumulative average velocity (10m - 60m) for

the Experimental Group

Table: 2b. Absolute difference of Pre-Test's average velocity with combined average velocities for Post Tests 1 and 2 of CONTROL GROUP.

Post-Test I

Tests

Pre-Tes t

Post-Test 2 1 6.6375 1 6.8725 1 6.8255 1 1

Absolute Increase

V1 10m - 20m 6.8 100

Percentage Difference

V2 20m - 60m 6.9625

= r6.9320 - 6.90551 = (- 0.0265) = (-0.0265 x 100)f 6.9320 = - 0.38 % = Increase in cumulative average velocity (10m - 60m) for

the Control Group

(VI + 4V2)/5 10m - 60m 6.9320

Summaxy

6.9320

opposite side of the track (Appendix D). The first beam, when broken by a

subject's sprint transit, initiated the counting of the first electronic digital timer

(EDT). Accelerating through the 20m mark, the sprinting subject broke the second

electronic beam at this 20m mark. The first EDT recorded this (1 0m to 20m)

transit tirne (to one-hundredth of a second).

The second beam served a dual function (Appendix D). In addition to

stopping the first timer, it simultaneously transmitted the break in pulse to start the

second timer. When a subject ran through the 60m mark the broken electronic

beam stopped the second clock. Thus the two transit times for sprinting through

the total 10m to 60m distance were recorded; the first from 10m to 20m, and the

second from 20m to 60rn.

3.600 TRAINING SCHEDULE

The duration of research testing was 10 weeks. All subjects met three times

a week on Monday, Wednesday and Friday between 5pm and 7pm. This time

period for the late aftemoon athletic session, was held unifomily constant across al1

warm up, plyometric and test run conditions. Both Experirnental and Control

Groups warmed up in a mixed rnanner. The warm up session lasted for 40

minutes. Subjects from each group did a pre-test sprint run after the first wann-up

session on day 1. Test runs were done at two-week intervals by both groups, for

the duration of the study. In total, there were 5 sprint mns, 1 pre-test sprint run,

and 5 post-test sprint mns. However, because of the sparsity of data after the

second test run, only the pre-test run and the first two post-test runs were used in

this study. The Experirnental Group performed the plyornetric treatrneit after the

warm-up at each session; and after the test run on test-run days.

3.700 WARM UP SESSION

The warm-up session lasted for 40 minutes, and constituted a mini workout.

At the end of each wam-up session, each subject had to be thoroughly activated to

be able to execute the 60m sprint test nin without any injury to the neuromuscular

or skeletal systems. The warm up protocol vaned slightly for each 3-week 1

microcycle period since the cardiovascular and neuromuscular systems adapted to

the regimen of the training stimulus (Bompa, 1993; Radcliffe and Farentinos,

1985). Subsequently, there subsequently was an increase in the intensity of sets,

with shortened recovery periods for total-body adaptations.

There were 5 sets of jogging / walking for the wann up exercises. Each set

consisted of two to three laps of slow jogging with intermittent retro- jogging, and

retro-walking. This was followed by a number of quadriceps and hamstring

stretches. These wann up exercises were increased in intensity, so that by the

fourth set of double-lap woik out, the subjects were actively doing stride-outs of

60m per 265m-lap to increase the range of limb motions, and physiological activity'

of gross limb muscles: gluteus maximus, quadriceps muscle group, hamstring

% group, gracilis, sartorius, gastrocnernius and soleus. Durhg recovery periods

between sets, the forward motion muscles, together with adductors and abductors

were stretched. Limbs were also flexed at joints to facilitate their range-of-motion.

Proper running technique was demonstrated and ernphasized without

atîempting any specific sprint run training. This was necessary to prevent any

adverse stresses to protagonist / antagonist muscle groups, which would be

unaccustomed to the dynamics of ground reaction forces that accompany

powerful leg implantations in çprinting. Keeping all çubjects injury - fric was of

paramount concem throughout the duration of this study. .

Set 1 consisted of two laps walking, and 1 lap of a very slow jog. Moderate 1

stretches of hamstring and groin muscles were performed for 2 to 3 minutes.

Set 2 consisted of a mixture of jogging and walking for 3 continuous laps,

followed by set 1 stretches, plus stretching the quadriceps mildly. The latter quad - stretch was executed with the knee Rexed, and the heel positioned at the gluteus

maximus, holding the instep with the ipsilateral hand. This knee flexor position

was maintained, and the entire flexed limb was rotated so that the knee rested at

the chest. This maximum hip - flexion, knee - flexion posture, concurrently

loosened up both joints, as foot - rotations at the ankle joint were done clockwise,

and counter- clockwise to loosen up the ankle flexors and extensorç. This lasted

for 3 to 4 minutes.

Set 3 consisted of 3 laps continuous jogging, foilowed by set 2 stretches. i

Left to right torso twists were performed, together with left to right am extensions,

and some upper body stretches. These stretches lasted for 4 to 5 minutes.

Set 4 consisted of mixed joggings and stridings for 3 continuous laps. Set

3 stretches were performed, and gentle squats loosened the hip flexors and

extensors, and any residual tightness that may have settled in the

lumbar region of the spine.

Set 5 consisted of altemate joggings and stridings for 3 continuous laps.

Set 4 stretches were executed, followed by elongate torso and body twists and leg

swingings for each leg.

Subjects were now fully warmed up to do the test sprint run. Specifically,

their quadriceps, hamstnngs, sartorius, gracilis and other thigh muscles were

warmed up and activated. On the shank, the gastrocnemius, soleus, peroneus

and other muscles were also fully warmed up and ready for explosive sprint

ninning activity. On sprint test nin days subjects did their sprint test nins.

However, on most days there was no test run, so that al1 subjects did a ten minute

cool down.

The cool down consisted of altemate jogging and walking, ai;S oxesr~ting

some of the above stretches (Shellock and Prentice, 1985; Radcliffe and

Farentinos, 1985; Bompa, 1993). The gradua1 cool down continued until a

subject's resting pulse was at 100 to 105 beats per minute. A similar cool down

regime was followed during the sprint run testing days.

The Experimental Group began the plyometric treatment immediately after

this cool down.

3.800 PLYOMETRIC EXERCISE TREATMENT

3.810 THE EXERCISE PROTOCOL

To initiate the plyometric rapid knee - lift exercise, subjects of the

Experimental Group stood next to a wall, or held on to a metal railing with one

hand, and rapidly moved the knee up and down through a 30 degree a k of

cuwature. This conctituted one cycle. Rapid, continuous up and down,

46

synchronous knee movements were executed for the timed 3-second duration of

the set. Each subject counted the number of cycles performed for a 3 second

period, and the counts were recorded by the experimenter.

The up and down knee movements were smooth, continuous, assiduous,

rapid, and deliberate through a small (25 to 30 degree) amplitude. This was the

unique performance criterion that was essential to elicit any significant

neuromuscular or rnyoelectrical potentiation of quadriceps and hamstrings (Bosco

et al, 1982; Bompa, 1993) during the plyometric treatment.

3.820 REST PERIOD BEnnlEEN SETS

Subjects rested for 3 to 5 minutes before beginning the next set. A total of

five sets were accomplished for each training session.

According to Bompa (1993), rapid knee - lift plyometrics is a multiple

response (MR) drill, and for high quality training, adequate rest between sets is

required for proper physiological regeneration. He states that the central

nervous system (CNS) that sends powerful signals to the active muscles, must

have a certain speed, power and frequency for optimum performance, and for high

quality training, the conduction vslocity of nervous transmission should not be

impaired by the fatigue of the woiking muscle. It has been suggested that a short

rest period of 1 to 2 minutes does not give adequate time for removal of anaerobic

metabolites. and recovery of both CNS and local muscular fatigue (Bornpa, 1993;

Gambetta, 1991). A fatigued neuronal system compromises its ability to send

powerful impulses for highly coordinated repetitive muscular activity (Bompa, 1993; :

Gambetta, 7991 ), and compromises excitation-contraction coupling at the

neurornuscular junction (Enoka et al., 1992). A fatigued state negates

47

appropriate CNS's involvement for optimal execution or motor leaming of a

coordinative skill (Bompa, 1993; Gambetta, 1991 ). Bompa (1 993) also suggests

that a rest period of 5 minutes should be optimal for a moderate plyometric activity,

and up to 15 minutes of rest between sets for a high intensity activity as the depth

jump.

3.830 MUSCLES AFFECTED BY THE PLYOMETRIC TRAINING

A cyclic, rapid knee raise and lowering sequence involves muscular

torques acting concurrently on the hip, knee and ankle joints. Muscles affected

by this plyometric training are mainly hip flexors and extensors, knee flexors and

extensors, and to a small extent, ankle flexors and extensors.

The hip flexors are: rectus femoris, adductor longus, tensor fasciae latae;

and sartorius (weakly, because of concurrent knee flexion).

Hip extensors affected are: biceps femons and semirnembranosus (mainly);

and semitendinosus (weakly, because of concurrent knee flexion); together witn

gluteus maximus (for hip extension greater than 15 degrees from the vertical).

Knee flexors affected are: the entire hamstring group (that are primarily knee

flexors, and secondarily hip extensors); together with gastrocnemius and popliteus

muscles.

Knee extensors affected are: the quadriceps group consisting of rectus

fernoris and vasti lateralis, intermedius and medialis muscles.

Very minor plantarflexion and dorsiflexion occur because of the foot

remaining parallel with the floor during the plyornetric knee raises exercise (Chu & :

Korchemny, 1989; Thompson, 1989).

48

3.840 MUSCLES THAT GO THROUGH THE STRETCH-SHORTENING

CYCLE OF THE PLYOMETRIC EXERCISE

During a rapid knee raise that involves hip flexion, in the ascending part of

the movement, the quadriceps are pre-stretched eccentrically as the load torque is

greater than the muscle torque. This should favour the synchronous potentiation

l effects of stored elastic energy, the myotatic reflex and myoelectrical effects to

increase the imminent concentric torque (Bosco and Komi, 1979; Bosco, et al.,

1981 ; Bosco et al., 1982; Komi, 1992; Thys et al., 1972). The consequent rapid

knee lowering increases the mechanical energy of the concentric contraction.

On the dorsal side of the thigh, the antagonist muscles, the hamstrings

undergo a similar movernent pattern of the SSC, of the above, that is they are pre-

stretched eccentrically with knee raises, and contract concentncally with knee

lowerings. ,

3.850 RANGE OF MOIIONS OF PLYOMETRICS AND SPRINTING

The range of motion of a plyometric knee Iift and lowering is much smaller

than that of a sprinter's step from toe off of stance leg, through that leg flight's phase 1

to foot at touchdown. With the hip flexion of a plyometric knee lift, the thigh transits

through an arc of 25 to 30 degrees ot curvature from the vertical, and represents

the knee lift phase. A knee lowering goes through the same amplitude of motion,

from flexed leg, to full extension.

The range of motion of a sprinter's stnde from full extension of stance leg at

ground contact, to the maximum knee flexion in mid-flight position, goes through ?

85 to 90 degrees for dite sprinters. There is a 60 degree hiatus of the flight phase

of a sprinter's step that this plyometric exercise does not represent, as only the firçt

49

and last 25 to 30 degrees of the stride phase are represented. However , because 1

of smaller amplitude of the knee lift and loweting of this plyomettic exercise to

generate a faster cyclic frequency, and shorter coupling time compared with that of

a sprinter's step, there is possible scope for a greater potentiation effect (Komi,

1 992).

The toe-off amortization phase in sprinting, with beginning of knee flexion, is

similar to that of the knee lift in plyometrics, and the braking phase of a sprinter's

rigidified leg just before ground contact is akin !O that of the final phase of a knee

lowering. Both (braking phase) actions slow down the leg just before ground

contact.

3.860 THE STEP AND STRIDE OF A SPRINT RUN

Dunng a sprint run, two steps, one by each leg in sequence, constitute a

stride. The stride pattern consists of two intgerdigitated steps (one for each leg).

When the stance leg either begins or ends its step cycle, the trail leg is always in

the middle of as flight cycle. The dite sprinter exhibits a short ground contact time

at foot implant. The greatly amortized leg extension at push-off with heel on, toe

off, powers the slowed down leg. A fully extended stance leg at ground contact is

pattemed by the contra (trail) leg fully flexed with its heel at the buttocks in the

rniddle of its stride cycle. This suddenly shortened lever-am of the leg, shifts the

leg's mass toward the hip joint, and effectively lessens the distribution of mass

about the entire leg. Bacause the leg's rotational axis is now suddenly

shortened, its moment of inertia is decreased, and to consenre energy, the thigh's

rotational torque is, as a consequence, increased (Enoka, 1994). This hcrease in

energy is efficiently transferred to the knee extension phase of the leg in flight

50

phase by the dite sprinter. The completed step movement is repeated in tandem,

for each leg during a sprint run.

3.870 PLYOMETRIC PROTOCOL FOR THE MICROCYCLES

This project included an initial ons week phase of orientation for

adjustments to warm-up capacity and tolerance by al1 subjects to the exercise

routines, and to determine an initial frequency of rapid knee lifts that would be

compatible for the Experimental subjects. After this first week, there were three i

microcycle periods, each of a 3-week duration.

For week 1, Experirnental subjects established their coordination pattern

with a synchronous, compatible exercise frequency. A 3-second cycle was found

to be compatible.

For microcycle 1, subjects did 5 sets of the plyornetrics for a 3-second

period.

For microcycle 2, subjects did 5 sets of the plyometrics for a 4-second

petiod.

For microcycle 3, subjects did 5 sets of the plyornetrics for a 8second

period.

For microcycle 4, subjects did 6 sets of the plyometrics for a 6-second

l period.

Sumrnafly, there was a one week period of conditioning, plus three 3-week

microcycles for the plyometric exercise protocol.

1

3.900 THE 60 - METRE SPRINT TEST RUN

On the day of a test run, each subject did the 60m sprint test run directly

51

after the warm up exercise. The subject began the run at Zhe Om mark and

sprinted as fast as possible through the 60m mark (Appendix D).

For each 60m sprint run, two transit times were recordecl; the firçt from the

10m to 20m mark, and the second from the 20m to 60m mark. Two persons

counted the number of strides that the subjed took to complete the 10m to 60m

distance. The two persons checking frequencies mitigatea any possible errors of

the s?ridacount tally. An experimental assistant positioned at the 20m mark,

counted the number of strides from the 20m to the 60m mark, to the nearest whole

stride; the other assistant stationed at the 60m mark duplicated this stride / distance

count.

Each subject initiated the 60m sprint run by standing at the Orn median of

the track. They started on their own, and sprinted through the 60m distance as

fast as possible.

The average velocities V I and V2 were derived from the two parts of the

acceleration phase (representing whole-body speeds for 10m to 20m; and 20m to

6Om), respectively.

Since maximum sprinting performance warranted a fully warmed up

muscular status, it was necessary for al1 participants to be constantly active. A

subject's wamed up status tended to maintain the integnty of their reflex

potentiation of large group muscle activation needed for a maximally powered

sprint effort (Shellock & Prentice, 1985). Upon completion of the run, each subject

immediately palpated their maximum heart rate for the first 15 seconds only, as a

full minute pulse decays exponentially after a maximum exercise activity (personal :

experience and observations).

Three runs were attempted by each subject, and only the fastest tirne of any

Table 5: Pearson Product Moment Correiation Matrix for Kneelift Rate and Sprint Times for Pretest and Post Tests

Pretest

Post Test 1

Post Test 2

Kneelift Rate 1 Pretest

single run, together with stride tally and pulse rate per minute, were recorded.

3.91 0 DATA COLLECTION

For performance and data collection purposes, each subject was given a

number. Mernbers of the Experimental Group were even numbered, and those of

the Control Group odd numbered. Performance activities were perfomed

randomly, and not in any sequential nurnerkal order. Colour - coded, yellow 3 x 5

inch cards were designated for the Control Group, and blue for the Experirnental

Group. Each pre-tabulated card had entries for al1 the parameters required for the

experirnent, such as resting and elevated heart rates, number of full cycles for the

plyornetric knee lifts and electronically recorded times for the test sprint runs.

3.920 STATISTICAL PROCEDURES

The velocity data was statistically analyzed by means of a Groups

(Experimental and Control) by velocity distances (10m to 20m), and (20m to 60m)

by tests (pre-test, post-test 1 and post-test 2) with repeated measures on the last

two factors. Of the single pre-test and five post-tests that this study accomplished,

only the single pre-test and the first two post tests in sequence were subjected to

statistical analysis. The three tests selected for the present statistics were done in

sequence early in the ten-week period of the study. Post tests 3,4,and 5 followed

in sequence at regular two-week intervals. Due to sparsity of data for post tests

3, 4, and 5, the results provided insufficient information for statistical inclusion in

the study. ?

CHAPTER 4

RESULTS

The statistical analysis was conducted on the largest group of subjects and

trials that had complete data available. In the Experimental Group there were five

subjects with three sets of data. The Control Group had four subjects with the

same test scores available. Statistical significance of the results was calculated at

an alpha level of 0.05.

The plyometric treatment on the Experimental Group was the independent

variable, and velocity rneasures of whole-body sprint running speeds, the

dependent variable. The Control Group did not experience the plyometnc

treatment. Both Groups had rneasures of their sprint test r ins at the beginning of

the experimental period, and at the end of each two week period.

Results represented the average sprint velocities V I for the 10m to 20m

distance, and V2 for the 20m to 60m distance for the three sprint run tests (Pre-test,

Post-test 1 and Post test 2). The average velocity V I also represented the sprint

phase 1 (SP 1) of the 60m sprint run, and V2 the sprint phase 2 (SP 2). The

overall average velocity for each subject is the average of V I and V2 pro-rated

over the (IOm, and 40m) different distances. Summady, the 60m distance was

run, but distance-times were collected for the last 50m distance as two contiguous

average velocities VI, and V2, now averaged as one average velocity reading.

4.1 00 ANOVA ANALYSES

The Groups by Sprint Phases by tests ANOVA (2x2) with repeated

measures on the last two factors, failed to identify a Groups main effect (F (1,8) =

0.26, p = .63) and a Trials main effect (F (2, 16) = 1.17, p = 0.34). However, the

results did indicate that there was a Sprint Phase main effect, with the 10m to 20m

distance being nin at a significantly slower velocity than the 20m to 60m velocity

distance (F (2,8) = 6.746, p = 0.03).

The various interactions did not reach statistical significance; Groups by

Sprint Phase interaction (F (1,8) = 0.661, p = 0.44), Groups by Tests interaction (F

(2,16) = 1 .l8, p = 0.33), Sprint Phase by Tests interaction (F (2,16) = 1.1 8, p =

0.33), Sprint phase by Tests interaction (F (2,16) = 1.1 42, p = 0.35), and the

Groups by Sprint Phase by Tests interaction (F (2,16) = 0.28, p = 0.76).

These results appear to have some face validity, in that there was an

expected difference in the velocities at the various distances. However, the lack of

additional significance is a concem, which may be due primady to the difficulty of

subjects to maintain the integrity of the training regime. The results did seem to

suggest a positive impact on the Experimental Group for the two Sprint Phases

(Figure 4 ), however this effect was not suffkiently strong to allow for statistical

support.

4.200 60 - METRE SPRINT TEST RUNS

For purposes of this study, the 60m sprint test run (which is the acceleration

phase of the lOOm sprint event), has been sub-divided into three sub-set :

acceleration phases. Acceleration phase 1 (AP l) , is from O m to 10 m. 1

Acceleration phase 2 (AP 2), transits from 10 m to 20 m, and the final acceleration

55

phase 3 (AP 3), concludes the last segment of this 60 metres. Velocity readings

were not taken for subjects' transits through the initial first 10 metres, as the study

was not designed to examine rapid changes in veloc%ies at the start of the run.

Both graphic and tabulated results are based on average velocity values for

acceleration phase 2 (10m to 20m), and acceleration phase 3 (20m to 60m) of the

60m sprint test runs.

There was a 6.30 % increase in average velocities over the last 50m (of the

60m run) for the 5 subjects of the Experimental Group, and a corresponding

decrease of 0.38 % for subjects of the Control Group (Apendix A). These values

represent the first four weeks of the scheduled ten - week period of the study.

Discontinuous values for subjects' intermittent participations in the test run and

plyometric treatment exercises, invalidated their inclusion in computations of the

final results.

Graphic display of average velocities for the acceleration phases 1 (10m to

20m), and 2 (20m to 60m) shows the matched values for the three continuous test

runs. (Appendix A). These values are for the pre-test and post - tests 1 and 2 sprint

runs. The initial 50 rn average velocity value for the combined acceleration

phases 2 and 3 for both the Experimental and Control Groups in the pre - test runs

were 6.36 mls and 6.93 m/s, respectively; and final average velocity values in post - tests 1 and 2 were 6.76 m/s and 6.82 rnls respectively for Experimental and

Control Groups.

4.300 PLYOMETRIC RAPID KNEE LlFW

fable 4 indicateç the anay of resultç for the treatment rapid knee-hft

frequency protocol on Experimental Group subjects over the two 2-week

microcycle periods for pre-?est, and post-tests 1 and 2. The pre-test's initial 3.5

knee-lifts per second (Ips) over a three second perÎod, was increased to a

sustained 3.8 Ips over an increased 4-second period for microcycles 1 and 2.

This 0.2 rate of knee-lift increase is equivalent to a 5.7 % increase in leamed 1

efficiency of the skill.

Correlation coefficients from the Experirnental Group and the two test sprint

runs, for the plyometric rapid knee lift frequencies for matched subjects of the

Experimental Group corresponding to those of the test sprint runs, are shown in

Table 5. Figure 1 shows the test effects that this exercise protocol may have had

on subjects stride frequencies during the corresponding test sprint nins.

There was no significant association between the sttide frequency of the

plyometric knee lift protocol and the test sprint runs. The results of the correlation

coefficient analyses indicate no association (r = 0.082) between the frequency of

the plyometric knee lifts for pre-test Experimental Group subjects and their stride

frequency performance in the 50 m pre-test sprint runs. Corresponding , i

comparative knee-lift frequency association for post-tests 1 and 2 are also poor

(r=-0.241). A high positive relationship (r = 0.852) was found for pre-test and

post-test 1 results, for stride frequency associations between pre-test with post-test

2; (r=0.884) and post-test 1 with post-test 2 results (r=0.984).

During the first week of the study, the Experimental Group found it difficult to

maintain coordination of a rapid knee lift frequency for more than 3 seconds. This

finding was the rationale for mandating the initial 3-second penod for rapid knee-

lift performance. I

It was hoped that there would have been a much higher correlation between

knee-lift frequency and stride frequency. Lack of precision in counting the stride

Figure 1. Graphed results of Dataset for V I and V2 Average Velocities of Experimental and Control Groups

* 62000

I t I

6.0000 i !

5.8000 Pre-Test Pd-Test 1 Poçt-Test 2

Sprint Test Runs

20m - 60m Control V2

6.9625 7.0425 6.8725

1Om -6Om Experimental ave

6.3624 6.8716 6.6552

20m - 60m Experimental V2

6.3460 6.9340 6.6820

Test Runs Pre-Test Post-Test 1 Post-Test 2

10m - 20m Experimental V I

6.4280 6 -6220 6.5480

frequency visually instead of using a video camera is perhaps a fundamental

reason for this weak relationship, as there was no redress to ascertain. or indeed

correct any possible human error of visually tracking the striding leg between fixed

points, and maintaining an accurate tally. This leamed transfer of rapid knee-lift

efFkiency and speed were some of the original assumptions in this thesis.

4.400 SUMMARY OF RESULTS

A remarkable aspect of the resuits is the decrease in values for average

velocities (AV) of the combined Acceleration Phases 2 (10m to 20rn), and 3 (20m

to 60m) representing the 50rn tested distance for both Groups after the first post - test sprint test run. This was followed by an increase in AV's for the two

acceleration phases for the Experimental Group, and acceleration phase 3 for the

Control Group of the previous post - test 1.

Reference to Tables 2a, 2b, for both EG and CG shows that following the

pre - test runs, there have been two consecutive increases in AV values for one

subject (a 37 year old marathon runner) of the Experimental Group matched with

two sirnilar increases for a (51 year old aerobic training athlete) Control Group

su bject.

There was a corresponding decline in efficiency as the study continued. A

training effect should occur as a result of an exercise programme with an

expected increase in exercise performance due to the body's adaptation to the

training regime (Bompa, 1993; Radcliffe and Farentinos, 1986); however, the

decreases in sprinting efficiency (except in overall average sprinting velocity of the

Experimental Group) is quite puuling.

It is tempting to speculate that plyometrics had a negative effect on subjects'

average velocities. Both Groups show lessening average velocity trends after the

initial pre - test runs. Had the imposition of a plyometric regime a negative effect

on subjects ninning speeds, the final trend of percent increases in average

velocities for subjects of the Experimental Group should have been more negative

than that of the Control Group. Some unknown aspect of the study adversely

affected thenormalisation of the results for Control subjects for the downward

graphic trend. This negative trend must be assumed to have affected a more

positive outcome for the Experimental Group. The validity of the negative trend,

however, is weakened by the small number of subjects of the Control Group in this

study.

Without the plyornetric treatment on the Experimental Group, a decrease or

increase of half a percentage point could have been expected, based on a similar

value experienced for the Control Group. But the imposition of a rapid knee lift

protocol which the Experimental Group experienced, and its accompanying 6.30 %

increase in average velocity value, positively supports the hypothesis of this study,

and effectively questions the validity of the merits of an assumed adverse or

negative influence that plyometrics may have had on the recorded status of

Experimental subjects' average velocities in their test sprint nins.

Any negative effect of the plyometric treatment should have significantly

lowered average velocity values of the Experimental Group significantly than those

that correspond to the Control Group's values.

4.500 KNEE - L I R S RELATEDNESS TO STRIDE FREQUENCY t

There was no significant association between the stride frequency of the

plyometric knee Iift protocol and the test sprint runs (see Table 3). The results of

KneeLllt PreTest Post 1 PreTest 0.082 POS~ 1 -0.241 0.852 POSE -0.091 0.884 0.984

- - - .- POSE

+ Post 1 + PreTest -_---

Test Runs

Figure 3. Graphed Results of Dataset for Pearson's Correlation Coefficient Analysls of Knee Lifts wlth Stride Frequency for 3 Sprint Test Runs

Table 3: ANOVA surnmary, error analysis by method of least squares

Table 4: Experirnental Group comparative stride frequencies of the knee lift protocol rnatched with the stride frequency of the 50m spriint nrn

Source of ' Variation G Error V GV

d f

1 7 1 1

Epsilon Correction

Sum of Squares

0.859 23.359 0.398 0.035

Microcycle

1 2 3 4 5

1 .O0 ,

A

Knee Lift Protocol

3.5 3.8 3.8 3.0 4.3

Stride Frequency per second

Mean Square

0.859 3.337 0.398 0.035

Error IT

Pre-Test 1.99 2.28 1-82 i -75 1.76

0.053 0.199

F

0.257

7.463 0.661

1 GT Error W GVT Error

7 2

Post Test1 2.1 2 2.32 2.05 1 -86 1.61

P

0-6276

0.293 0.4429

1.185

1.142 0.280

1 -1 69 0.373 0.397

Post-Test 2 2.16 2.35 2.04 1.74 1 -60

0.3391 2

14 2 2

14

0.3345

0.3471 0.7598

0.79 0.403 2.377 0.155 0.038 0.949

0.201 0.170 0.077 0.019 0.068

correlation coefficient analyses indicate a weak association (r = 0.082) between

the frequency of the plyometric knee Iifts for pre-test Experimental Group subjects 1

and their stride frequency performance in the 50 rn pre-test sprint nins.

Correspondingly, the comparative knee-lift frequency associations with Post-Tests

1 and 2 were even weaker (r= -0.241 and r = -0.091). A high correlation (r = 0.852)

was achieved for relatedness of pre-test and post-test 1 results, and r= 0.884 and

r= 0.984 correlations for stride frequency associations between pre-test with pst-

test 2; and post-test 1 with post-test 2 results.

4.600 POST - TEST 2 AVERAGE VELOCITY DECREASES

A cursory examination of Figure 1, shows a slight decrease in average

velocity ( -0.388%) for the Control Group that did not experience the plyometric

rapid knee lift treatment. This begs a logical explanation. Less than 1 %

i variability of sprint test run performances is perhaps well within the limits of

repeatability of test error for this study. A factor in the interpretation of this study is

the comparative performance of the Control Group which maintained a relatively

constant sprinting performance in the three test mns.

In consideration of al1 subjects who participated in this study (not just those

used for statistical analyses), most of the subjects showed a decrease in average

50 rn sprint velocities after the first test nin. Two triathletes, one from each Group

showed similar average velocity increase for the first post - test nin, and

subsequent decrease for the second post - test run. This parallels sirnilar trends

for both Groups. The triathletes non-aberrant decreases in values would tend to .,

mie out their participation in strenuous practice or indeed in competitive activities

i for this period. Meterologic data for the intervening test period had daytirne high

temperatures above twenty degrees Celsius, thus, al1 of the subjects working at

their recreation activities in sunny, dry weather, could have affected the energy

levels required for highly efficient performance sprinting in post - test run 2.

4.700 AlTRlTlON OF SUBJECTS

Of the thirty subjects who signed up to volunteer for participation in this

study, attrition over the ten week period, reduced the fifteen mernbers for each

Group to ten for the Experirnental Group, and six for the Control Group. Lack of

continuous data for these reduced numbers, subsequently reduced the final

number of subjects to five for the the Experimental Group, and four for the Control

Group.

Although there was adequate control of most factors of this study, loss of

subjects tend to threaten the validwQ of the results. Reasons for these reduced

nurnbers are speculative at best. As noted earlier, over-exposure to hot, sunny

week ends, and possible over exertion while recreating may have sapped the

subjects' energies. The lack of motivation to exert one's self maxirnally in an

unaccustomed activity such as sprinting, or any othe motivational factor could also

be responsible for average velocity decreases that occurred. This study was

conducted during the period of the Atlanta Olympics, and television (TV) viewing

times for finals of most events conflicted with the early evening time-period of this

study. Ordinarily, suppertime remains a 'prime-time' for TV viewing with family

bonding periods for those subjects who were also parents.

The experimenter had to be careful of over-intensive interventions to an ?

adult group of subjects. As a teacher and athletic coach with many years of

experience, and having completed a graduate course on designing interventions to

iwrease subjects performances, I believe that the interventions were quite

adequate to maintain a high level of motivation with the subjects.

After the study was completed, some subjects complained that the track

surface was too hard on their feet and adversely affected their mnning cornfor?.

Forces generated during a high intensity sprint run are about four times as great

as during a casual jog. Such an increase would have been noticed even on a

grass surface for those unaccustomed to fast running. This perception was

perhaps unjustified, as Provincial track and field events, sanctioned jointly by

Sport Nova Scotia, and Athletics Canada take place regularly at the Dalplex

venue. To the best of the author's knowledge, no athlete has ever complained

about the track's surface. 1 have used this surface since 1982, and have found R

to adequately suit the sprinting styles of myself and athletes whom I have trained,

and seen on this track over the years. The Dalplex track surface is rubberized and

quite cornpliant in its capacity to absorb some of the energies of a ninner's foot

implant. Also, the temperature of the field house during the hot summer months

should have increased the rubberized surface's compliancy, and this increased

'softness' should tend to contra-indicate a perception of a hard, extra-fast

surface.

CHAPTER 5

DISCUSSION

5.000 OVERVIEVV

Sparsity of continuous data tends to weaken the possible conclusions of this

study, and as such threatens its validity. The results reflect the findings of five

subjects from the Experimental Group, and four from the Control Group over a four - week period of the scheduled ten-weeks originally proposed for the study.

However, the 6.30 % increase in average velocities for the Experimental Group as

compared with a 0.38 % decrease for the Control Group, is within the statistical

probability of 0.0293. This factor tends to strengthen the validity of the study.

5.1 00 ANTHROPOMETRIC DATA

Reference to the anthropometric data (of Table 1) shows the average age of

Experimental Group subjects to be 41 years, and that of the Control Group to be 36

years. Graphed results of average sprinting velocities (Figures l a and 1 b) show

Experimental subjects with a 6.36 % average pre-test velocity cornpared with 6.93

% for the Control Group, indicates the latter value to be 8.96 % greater than the

Experimental Group. This is somewhat punling for an older Group of subjects

(mean difference of five years) that perhaps might have had slower sprint

performances, since both groups seemed matched in gross comparative and

generalized anthropometric characteristics.

There is a casual jogger, a triathlete and a non-athletic subject in each

Group. The Control Group has the only fernale subject whose results are included

i 63

in this study. From a physiological point of view, a closer examination of the

Control Group's maximum heart rate obtained immediately after their sprint test

runs measured 160 beats per minute (BPM), as compared with the Experirnental

Group's value of 162 BPM, with resting heart rates of 52 bpm for the Control

subjects and 56 bpm for the Experimental subjects.

5.200 PLYOMETRICS SPEED OF TRAINING COMPARED WlTH

PREVIOUS STUDIES

Because of a 6.30 % increase in whole-body movement speeds of the

Experimental Group using the plyometric treatment protocol, the training effect of

this rapid knee lift plyometric exercise seerns to be the only causative factor. The r

rapid knee raises and lowerings seem to have aided the legs' powered

movements in sprinting. This increase was possibly caused by the elastic

mechanical energy stored in the thighs' muscles that were stretched during the

negative work phase of the eccentric elongation contraction of the legs' extensor

muscles. Released stress energy as nascent, kinetic energy was subsequently

and imrnediately used to increase the mechanical efficiency of positive work of the

concentric contraction phases during sprinting. Enhancement of concentric force

seems the likely candidate for increased speeds of the Experirnental Group of

Su bjects.

There is a similarity beniveen this research finding and that of Thys et al.,

(1972) where a deep knee bend and rising to the erect position protocol, with and i

without delay caused a 0.26 increase in mechanical efficiency (26 %) of the

'rebound' subjects that did not pause at the knee flexion stage. This 'ribound' of

the leg extension followed immediately by fiexion, experienced a greater speed of

muscle shortening. The shortening being the sum of the speed of the contractile

elements, plus that of the elastic series elernents that were stretched in the

negative work eccentric extension phase. Hem, the negative work of flexion was

partiy transferred into elastic energy in the legs' eccentrically stretched extensors

that were subsequently utilized to perfom positive woik.

Asmussen and Bonde-Petersen's (1 974a) study on subjects perfonning

depth jumps from different heights found that the negative mechanical energy

utilized by the leg extensor muscles as elastic energy, varied positively with heights

from which the subjects jumped. Here the muscles were forcibly stretched while

they actively resisted movement, since they performed eccentric contractions

while doing negative work. The phase of negative work was immediately followed

by the positive work phase in which the muscles were shortening. Increases of

22.9 %, 13.2 %, and 3.3 % in mechanical efkiency for jump heights were due to

elastic energy stored in the series elastic components of muscle. These

researchers assumed that the elastic components were stretched according to

maximum tensions developed from the heights jumped. voluntarily by the

contractile mechanism, but that a discrete tension above that was produced

temporaiily by the rapid stretching of the legs' elastic components by gravity.

EMG activities of the soleus, and vastus lateralis muscles increased just before

touchdown. Again the temporary storage of elastic energy in the short range

stiffness that the muscles experienced, was cited as the possible causative factor

for increases in energy efficiencies.

A later study by Asmussen and Bonde-Petersen (1 974b), into treadmill

running with various resistances, and depth jumping with and without rebound,

found a 40 % greater efficiency of vasti muscles during the rebound, as compared

with a 24 % increase without rebound. This suggests that the series elastic

components' ability to tentatively store mechanical energy in the negative work

phase, brings about this additional energy during the positive work phase of

concentric contraction.

Similarly, works by Bosco and Komi (1 979), Bosco, et al., (1 98l), and

Bosco et al., (1982), all suggested that the series elastic components were the

possible storage sites for elastic energy potentiated during the negative work

phase of the eccentric elongation contraction, that immediately preceded the

concentric shortening phase.

Bosco and Komi's (1 979) findings that the cornbined utkation of elastic

energy and myoelectrical potentiation of the muscle activation, caused the

increases in energy effkiency, suggests that the improved performance of

activities that involved the use of the stretch-shortening cycle in this study, may

have been attributed mainly to the restitution of elastic energy. However, the study

by Bosco et al., (1982) has shown that myoelectrkal potentiation might have

occurred in the late stage of activities that involve the stretch - shortening cycle.

The enhanced neural potentiation was either via spinal or cortical reflexes.

It is suggested that high motor unit activation during the plyometric knee lift

exercise, with the simultaneous increase in force of the eccentric contraction with

increased stiffness of muscle, should favour a condition for optimal potentiation of

muscular performance in the subsequent concentnc contraction phase. This

increased potentiation resulting from the rapid knee lifi exercise, is suspected

the primary cause of the training effect that powered leg movements toward

increased running speedç of the Experirnental Group. The concept oi short

to be

range

stiffness of srnail knee amplitude of the plyometric treatment seemed to have

caused the suspected high eccentric torque.

According to Bompa (1 993), plyometrics is quite suited to work within

cornplex neural mechanisms, and its training produces significant changes, both at

muscular and at neural levels that facilitate and enhance the performance of faster,

and indeed, more powerful movernent skills. The short, but intense plyometric

knee lift protocol seems to have done just that.

Sumrnarily, the plyometric rapid knee lift exercise through a small amplitude,

seemed to have conditioned a faster movement cadence on leg extensor and

flexor muscles. Faster cyclic leg rotations of the sprinting action are caused by

increased conduction velocities of the vasti and hamstring groups of muscles

(Komi and Bosco, 1978 ). The increased force of stretched vasti and hamstring

muscles caused reflex potentiations of the stretch reflex, which caused increased

muscle stiffness that favoured a short coupling tirne. Cumulatively, these factors

are assumed to be the probable cause for conditions that may have facilitated

excellent potentiations of muscular performance in the subsequent concentric

phases of the stretch-shortening cycle, together with greater magnitudes of force,

and increased speed of muscle shortening for greater leg power (of the

Experimental Group) during sprinting (Komi and Bosco, 1978; Bosco and Komi,

1981,1982; Komi, 1992).

5.300 IMPLICATIONS FOR FURTHER STUDY

Subject drop out, as well as incornplete data over the 10 - week period,

suggest the need for more subjects who would complete a study over its intended

duration. There is a need for younger çubjectç, who are highly motivafed elite

athletes, and who would be inclined to see short-terni and long-term benefits

resulting from such a study.

Future studies that involve the use of of plyometric exercises to mimic the

range of motion of the sport or other activity involving the stretch-shortening cycle,

could possibly have significant benefits for powered activities where quick

response gives both a diminished time and increase of force and a powered

advantage for the subject.

Future studies should enquire into correlations between the frequency of a

plyornetric protocol with the stride frequency of limb movements that the exercise

simulates. Research should also be directed to probe into other possible causes

for the increases in power attributed to the stretch-shortening cycle, besides

storage of elasticized mechanical energy, reflex potentiation of the rnyotatic reflex,

and enhanced myoelectrical activity of the forcibly stretched muscles. The force

aspect of the enhanced power factor attributed to the SSC, have invoked active

research, however, there is a need for studies specifically designed and carried out

to probe into the possible role of the cortex's plasticity that may enable it to alter

(and increase) its impulse firing frequency sent to the gross limb muscles.

5.400 CONCLUSION

This study could have been much stronger in intemal validity, it was limited

by too few subjects participating over too short a time period. This would also

have increased its extemal validity to a larger potential population.

The 6.30 % increase in mechanical efficiency expressed as increases in

average velocities of the Experimental Group over the Control Group, shows a

trend to support the main hypothesis of this thesis. The frequency of the plyometric

knee lifts had no effect on frequency of limb movernent of the test sprint run. The

68

t

correlation coefficient data of frequency of plyometric limb movements and stride

frequencies, have not supported some of the original assurnptions about the

benefits of plyometric training.

Appendix A: Exparimental Group Data for ail Subjects and Tests. Mean Times for V I and V2

Subjects

A 6 C D E F G H \ J

-

Pretest Postests

Appendix 6: Control Gmup Data for al1 Subjects and Tests. Mean Times for V I and V2

Subjects

A 8 C D E F

Appandi C: ~ n c o u r s e oi the Ddple~ lndoor Tm&, Showhg ttie Location of the Three S d a y Unked Transnitting-ReceMng -Recordfng Stations at the IOm, 20m and 60m Oistances

Appendix F: PAR-Q and You

Appendix E: Consent Form

CONSENT FORM

REFERENCES

Aagard, P., Simonsen, E.B., Trolle, M., Bangsbo, J., & Klausen, K. (1996). - Specificity on Training Velocity and Training Load on Gains in

lsokinetic Knee Joint Strength. Acta Phvsioloaica Scandinavica,

156, 123-129.

Asmussen, E., 8 Bonde - Petersen, F. (1974a). Storage of Elastic Energy in

Skeletal Muscles in Man. Acta Phvsioloaica Scandinavie% 9L, 385-

392.

Asmussen, E., & Bonde - Petersen, Ç. (1 974b). Apparent Efficiency and

Storage of Elastic Energy in Human Muscles during Exercise. Acta

Physioloaica Scandinavie% 92 537-545.

Astrand, E. O., & Rodahl, K. (1986). Textbook of Work Physiology:

Physiological Bases of Exercise. (3rd. Ed.,) New York: Mc Graw Hill,

756.

Bellotti, P. (1 991 ). Some Considerations Conceming Speed Training. New . . udies rn Athlet CS. IAAF. 6(& 7-9. .

Bompa, T. (1993). Powet Training for Sport: Plyometrics for Maximum

Power Development. Mosaic Press. C o ~ h i n a Association of

Canada. Oakville. Ontario.

Bosco, C., & Komi, P.V. (1 981). Prestretch Potentiaüon of Human Skeletal

Muscle through Prestretching. Acta Ph

135-140.

Bosco, C., & Komi, P.V. (1979). Potentiation of the Mechanical Behaviour of

the Human Skeletal Muscle through Prestretching. acfa

hysiologica Scandinavica. 106: 467-472.

Bosco, C., Viitasalo, J. T., Komi, P.V., & Luhtanen, P. (1982). Combined

Effect of Elastic Energy and Myoelectrical Potentiation during Stretch-

Shoitening Cycle Exercise. m i o l c l o i ç a ScanQinavica. 1 14:

557-565.

Chu, D. (1984) Plyometric Exercise. National Strength and Condrtionirlg. .. .

. . ssociawn Journal. a. 56-59; 61-63.

Chu, D., & Korchemny, R. (1989). Sprinting Stride Actions: Analysis and .. . . . Evaluation. Mo-ength md Conditlg[ll[lO Association

JournalL 1 1 (Q, 6-8; 81-85.

Delecluse, C., Van-Coppenolle, H., Willems, E., Van-lem putte, M., Diels,

R., 8 Goris, M. (1995). Influence of High-resistance and High-velocity %

Training on Sprint Perfomiance. M-d aience in Sport% .

ercise. Indianapolis, Indiana. 27 CR), 1 203-1 209.

Dooley, P.C., Bach, J. M., & Luff, A. R. (1990). Effects of Vertical Jumping on

the Medial Gastrocnemius and Soleus Muscles of Rats. Journal of

Bpplied Phvsioloqy, 2004-201 1.

Enoka, R. M. (1 994). Neurornuscular Basis of Kinesiology. (Second Edition). . . Human Kinetic~, Windsor, Ontario.

Enoka, R. M., & Stuart, D. G. (1992). Fatigua Related Changes in Motor Unit

Activation Potentials of Adult Cats. Muscle & Newe, 19: 138-1 50.

Enoka, R. M. (1 983). Muscular Control of a Leamed Movement: The Speed

Control System Hypothesis. merimental Brain Research 135-

145.

Fung, Y .C. (1 993). Biomechanics: Mechanical Properties of Living Tissues.

Spn'nagr- Verlap, New York Inc.,

Gambetta, V. (1 991). Essential Considerations for the Development of a

Teaching Model for the 100 rnetres Sprint. New Studies in Athletics.

Intematiwal Athletic AssocaJon FedQmm . . .= 27-32.

Hakkinen, K., Korni, P. V., & Alen, M. (1 985). Effects of Electromyographic %

and Muscle Fibre Characteristics of Leg-extensor Muscles. Acta

Hutton, R. S. (1984). Acute Plasticity in Spinal Segmental Pathways with

use: Implications for Training. In M. Kumamoto (Ed), Neural and

Mechanical Control of Movement, 90-1 12. Kyoto: Yamaauchi Shote~.

Komi, P. V., & Bosco, C. (1 978). Utilkation of Stored Elastic Energy in Leg

Extensor Muscles by Men and Women. Juîeclictne and Sc . . ience in

S~orts & Exercise, 1 P14L 261 -265.

Korchemny, R. (1 985). Training Drills for Speed-related Events. National

Strenath and Conditionina Journqi, 67-69.

Korni, P. V. (1992). Stretch-shortening Cycle. In P. V. Komi (Edo), Strenath

and Power in S D O ~ . 169-3 7a. Champaign, Illinois. Human ~inetics.

Kirsch, R. F., & Rymer, W. 2. (1 987). Neural Compensation for Muscular

Fatigue:Evidence for Significant Force Regulation in Man. Journal of

oloay, a2, 1 893-1 91 0.

Mc Farlane, B. (1 982). Jumping Exercises. Track and Field Quarterl~

Review. 82141,5448.

Mc Fartane, B. (1993). Basic Technical Model for Speed. Canadkn Track & . . ield C o a ~ s s o c i a t t o n . 7-1 2.

\

Milner-Brown, S., & Miller, R. G. (1986). Muscle Membrane Excitation and

Impulse Propagation Velocity are reduced during Muscle Failure.

Muscle & Nerve. 9, 367-374.

Maton, B. (1991). Central Nervous System Changes in Fatigue lnduced by

Local Work. In SG. Atlan., L. Beliveau., & P. Bouissou. (Eds.),

Muscle Fatiaug: Biornechanical and Phvsioloaical Aspects, 207-221.

Paris: Masson.

Pearlman, A. L., 8 Collins, R. C. (1990). Neurobiology of Disease. Oxford

University Press. Oxford, U.K.

Putnam, C., 8 Kozey, J. (1989). Biomechanics of Sport : Substantive Issues

in Running. Ed., Vaughan, C. L. Chapter 1. 1-33. Boca Raton, C.R.C.

Press.

Radcliffe, J. C., & Farentinos, R. C. (1985). Plyometrics: Explosive Power

Training. 2nd. Ed., Champaign, Illinois. Human Kinetics Publishers,

127.

Schubert. B. (1991). The i l 1 World Championships in Athletics. f okyo,

1 99 1 : A General Analysis. New Studies in Athletics. htemational

Athletic Association Federat . . ion. 7 (1 7-1 4.

4

Sale, D. B. (1988). Neural Adaptation to Resistance Training. Medicine

ience in Sports and Exercisg, Ze (5L S135-S145.

Sale, D. G. (1 987). Influence of Exercise and Training on Motor Unit

Activation. Exercise and Sport Science Reviews. Vol. 1 5, Ed., K. B.

Pandolf. Mac Millan Publishina Co., Inc., New York, 95-1 51.

Shellock, F. G. & Prentice, W. E. (1985). Waming-up and Stretching for

lm proved P hysical Performance and Prevention of Sports-related

Injuries. S~orts Medicine, 2, 267-278.

Thompson , C. W. (1989). Manual of Structural Kinesiology. Eleventh

Edition. Times Minor / Mosby. collepe Publishing . . , Toronto.

Thys, H., Faraggiana, T.. & Margaria, R. (1 972). Utilization of Muscle

Elasticity in Exercise. J o u r n a l l i e d Ph sioloqy. 321 (4).

Veroshanski, Y. (1 969). Perspectives in the lmprovement of Speed-Strength

Preparation of Jumpers. Review of Soviet Phvsical Education and

m!&, 4 (2),28-29.

Veroshanski, V., & Tatyan, V. (1 983). Speed Strength Preparation of Future

Champions. Soviet Sports Review, 1 8 (41, 1 66-1 70.

i~nl i t LVALUAIIUN TEST TARGET (QA-3)

APPLIED A* IMAGE. lnc - 1653 East Main Street - -. - - Rochester, NY 14609 USA -- -- - - Phone: 71 6/482-O3ûô -- -- - - Fax: 71 W88-5989

O 1993, Applied Image. Incr. All Righis Resenied