Comparison of Aquatic and Land Plyometric Training on

Strength, Power and Agility

Dawn T. Gulick, PhD, PT, ATC, CSCS

Christina Libert, PT

Meghan O’Melia, PT

Laura Taylor, PT

Research Report

Widener University

Institute for Physical Therapy

This research was funded in part by a Widener University Provost Grant

2

Correspondence should be directed to:

Dawn T. Gulick, PhD, PT, ATC, CSCS

Associate Professor

Widener University

One University Place

Chester, PA 19013 USA

610-499-1287 (voice)

610-499-1231 (fax)

dtgulick@widener.edu

3

Acknowledgments:

The authors wish to thank Dr. Robert Wellmon, PhD, PT, NCS for his statistical

expertise, Mr. Bob Piotti for his cooperation in the use of the pool, and the Widener

University Grants and Awards Committee for their assistance in funding this

research.

4

Comparison of Aquatic and Land Plyometric Training on

Strength, Power and Agility

Abstract

BACKGROUND: Plyometrics are used to increase explosiveness and strength. Whereas,

aquatic activities are used to decrease joint compression forces via the benefits of

buoyancy. There is interesting potential in the blending of these two techniques.

PURPOSE: The purpose of this study was to compare the effectiveness of an aquatic and

a land plyometric program. SUBJECTS: Forty-two (24 female, 18 male; 24.5 ± 3.5 yrs)

volunteers were randomly divided into three groups: control, land, and aquatic.

METHODS: Each participant completed a pre-test, mid-test (after intervention phase I),

and post-test (after intervention phase II) protocol to assess quadriceps strength, power,

and agility. Intervention phases I and II included 4 (120-foot contacts) and 5 (180-foot

contacts) plyometric exercises, respectively. Each phase consisted of 6 sessions (2x/wk x

3 wks). RESULTS: ANOVA with repeated measures revealed a main effect for time for

all 3 dependent variables. Post-hoc analysis revealed a significant difference between the

control and experimental groups, as well as some differences between land and aquatic

groups. CONCLUSIONS: The implications of this study are that plyometric aquatics are

comparable to a land plyometric program. Furthermore, the protection of joints from

compression forces via the effects of buoyancy may make aquatic plyometrics a more

attractive form of training and rehabilitation.

KEY WORDS: aquatic exercise, plyometrics, strength, power, agility

5

Comparison of Aquatic and Land Plyometric Training on

Strength, Power and Agility

REVIEW OF THE LITERATURE

Introduction

Plyometrics involves a combination of eccentric and concentric muscle activity,

which allows the muscles to produce a greater force than typical concentric activities alone

(Wagner & Kocak, 1997). Plyometrics are known to help increase explosiveness and

strength of the lower extremities through use of vertical jumps, hops, and/or bounding

movements (Wilk, 1997). Sports involving jumping and sprinting have incorporated this

training technique to optimize performance. On the other hand, aquatic training has the

benefit of the buoyancy of the water. The water provides resistance to help strengthen the

muscles while reducing joint compression forces (Prins & Cutner, 1999; Thein & Brody,

1998). There is interesting potential in the blending of these two techniques.

Effectiveness of Plyometrics

In a current survey of training preferences, 94% of college strength and

conditioning coaches used plyometric training (Durell, Pujol, & Barnes, 2003). Plyometric

exercise utilizes the stretch-shortening cycle to train muscles to do more work in a short

amount of time (Holcomb, Lander, Rutland, & Wilson, 1996; Komi, 1988). In plyometric

exercise the muscle switches from an eccentric to concentric contraction, leaving little time

for the muscle to relax; the stored elastic energy of the muscle and stretch reflex together

allows the muscle to create a greater force (Hedrick & Anderson, 1996; Holcomb et al.,

6

1996; Komi, 1988). Plyometric training increases power output and vertical jump

performance (Luebbers et al., 2003; McLaughlin, 2001; Potteiger et al., 1999).

Luebbers et al. (2003) showed that four- and seven-week plyometric program

improved vertical jump height, vertical jump power, and anaerobic power. The increase

seen in muscle power production may be the result of muscle fiber size that would be

consistent with the observed increase in body mass of the participants. Likewise, Potteiger

et al. (1999) found that plyometric training increased leg power production and muscle

fiber size of both Type I and Type II fibers. This study also showed that 8-weeks of high

intensity, short rest interval plyometric training increased vertical jump height and VO2max

(Potteiger et al., 1999). McLaughlin (2001) demonstrated that plyometrics improves

explosiveness and endurance. However, plyometric training on land involves a high

degree of compressive forces on the joints and a sufficient level of strength must be present

to tolerate the eccentric forces.

Effectiveness of Aquatic Programs

Although exercising in the water has not been studied as much as on land, water is

known to help reduce joint stresses (Prins & Havriluk, 1991; Rivera, 1994; Thein & Brody,

1998). The success of aquatic rehabilitation is based on two properties of water: buoyancy

and viscosity (Prins & Cutner, 1999; Prins & Havriluk, 1991; Rivera, 1994). The effects

of buoyancy are immediately felt when one enters the water. Buoyancy decreases the

weight of an individual in proportion to the amount of the body immersed. Whereas, the

viscosity of the water cam be used to provide accommodating resistance (White & Smith,

1999). Water has been reported to offer twelve times the resistance of movement in air

7

resulting in significant muscle strengthening (White & Smith, 1999). But since the

resistance of the water corresponds to the force exerted, the likelihood of injury is notably

reduced in the water (Prins & Cutner, 1999; Prins & Havriluk, 1991; Rivera, 1994).

Effectiveness of Plyometrics in the Water

Three studies have explored aquatic plyometric training in healthy individuals with

slightly differing results (Martel, Harmer, Logan, & Parker, 2005; Miller, Berry, Bullard,

& Gilders, 2002; Robinson, Devor, Merrick, & Buckworth, 2004). Martel et al (2005)

reported significant increases in vertical jump and knee peak torque after six-weeks of

aquatic and land training programs. Robinson et al (2004) noted improvement in vertical

jump, peak torque, and peak velocity with both land and aquatic training after eight weeks.

However, the aquatic group experienced significantly less muscle soreness than the land

group. Whereas, Miller et al (2002) reported similar improvements in vertical jump,

power, and peak torque with no difference in muscle soreness.

Purpose

The purpose of this experiment was to examine the effectiveness of an aquatic-

based plyometric program compared to a land-based program in improving lower body

strength, power, and agility.

METHODS

Participants

Forty-two university students (24 female, 18 male; 24.5 ± 3.47 yrs; 73.65 ± 17.77

kg) with no formal training in plyometrics read and signed an informed consent approved

8

by the Widener University Institutional Review Board for the protection of human

subjects. Each participant completed a questionnaire to screen for present or prior lower

extremity injury. Each participant agreed to hold their activity level as constant as possible

for the duration of this study. The volunteers were randomly divided into three groups:

control, land, and aquatic.

Materials

A MicroFET hand-held dynamometer (Hoggin Industries, Draper, Utah) was used

to assess quadriceps strength. A pilot study was conducted with ten volunteers to assess

reliability of the device in the testing circumstances use (R=0.943). Intrarater reliability

was reported to be 0.93 by Potteiger (1999) and 0.9754 by Luebber et al. (2003). A

VerTech jumping system (VerTech Inc, Falls Church, VA) was used assess vertical jump.

The test-retest reliability of this device has been reported to be 0.93 (Martel et al., 2005).

A T-run was used to assess agility. This was a timed test that involved running forward 5-

meters, left laterally 5-meters, right laterally 10-meters, left laterally 5-meters, and

backwards 5-meters to the starting point (r= 0.836). Each point was designated by a mark

on the floor. This test was administered using the standardized format described by

Semenick (1990).

Procedure

Each participant completed a pre-test protocol to assess strength, power, and

agility. Strength was assessed via a maximal isometric contraction of the quadriceps

muscles at 45° of knee flexion. The measurement was performed with a MicroFET hand-

held dynamometer (HHD) while seated in a dynamometer chair with the lever arm locked

9

at 45° of knee flexion. This rigid stabilization (Figure 1) was used so the clinician’s upper

extremity strength was not a limiting factor in obtaining a maximal muscle contraction

(Kimura, Jefferson, Gulick, & Coll, 1996). The participant was instructed to crescendo to

a maximal muscle contraction over a 3-second duration. The force was recorded in pounds

per square inch. A total of three trials were performed with a 15-second rest between

trials. Research has demonstrated that a 3-4:1 (rest:work) recovery ratio is sufficient to

replenish the fuel supply for maximal subsequent bouts (McArdle, Katch, & Katch, 2001).

Power was assessed via a vertical jump test. Weight (in kilograms) was assessed at

each phase using the same standard medical scale. Participants performed three vertical

jumps with 15-seconds of rest between jumps (McArdle, Katch, & Katch, 2001). There

were no limitations placed on the depth of the squat prior to the vertical jump but

participants were required to begin with their arms at their side and to keep their feet on the

floor during the pre-jump movements, i.e. no approach/steps were permitted. The height

reached with the participant’s hand was recorded using a VerTech Jumping System. The

participant’s standing vertical reach was deducted from the mean of the three jumps to

calculate “jump height.” Peak power was calculated using the formula by Harman,

Rosenstein, Frykman, Rosenstein, and Kraemer (1991). In a study by Canavan and

Vescovi (2004), this equation was found to be more precise than other formulas at

estimating peak power.

Peak power (W) = [61.9 x jump height (cm)] + [36 x body mass (kg)] - 1822

10

Agility was assessed via a T-run. Each participant ran forward 5m, sidestepped

right 5m, sidestepped left 10m, sidestepped right 5m, and then ran backward 5m to the

starting position. A total of three runs were completed with a 30-second rest between trials

(McArdle, Katch, & Katch, 2001). The mean of the three trials were used for data

analysis.

Intervention Phase I involved a basic plyometric training program (Elite Training

Tips: Jump Around, 2000) with a total of 120-foot contacts. The four plyometric exercises

included ricochets, tuck jumps, high knee skips, and 18-inch box drops (Figure 2, 3, 4, 5).

Participants performed three-sets of ten repetitions of each exercise. The land-based and

aquatic-based training groups each performed the exact same exercises in the respective

mediums while the control group had no intervention. The training frequency was two

times per week for three weeks. The researchers oversaw the training sessions to assure

the safe and proper performance of the techniques. At the conclusion of Phase I, the pre-

test measurements were repeated in the standardized format (mid-test).

Intervention Phase II progressed the participant to an intermediate plyometric

program (Elite Training Tips: Jump Around, 2000) that included 180 foot contacts per

training session. The plyometric exercises performed on land or in the water were forward

and sideward ricochets over a hurdle (Figure 6), tuck jumps, high knee skips, and 18-inch

box drops. Training sessions included three-sets of 12 repetitions of each plyometric

exercise. Participants continued to train two times per week for three weeks. The

researchers oversaw the training sessions to assure the safe and proper performance of the

techniques. Upon completion of the twelve plyometric training sessions, all dependent

11

variables were re-assessed (Post-test). A summary of the entire intervention procedure is

displayed in Table 1.

Results

Means and standard errors for all variables across time are displayed in Table 2.

Analyses of variance with repeated measures revealed a main effect for time for all three

dependent variables. The results are displayed in Table 3. A comparison of the land and

aquatic influence on strength, power, and agility are displayed in Figures 7, 8, and 9,

respectively.

Clinical Relevance

The results of this study are similar to that of previous studies (Martel et al, 2005;

Miller et al, 2002; Robinson et al, 2004; White, & Smith, 1999; Wyatt, Milam, Manske, &

Deere, 2001). This study demonstrated that both land and aquatic plyometrics are effective

in improving strength, power, and agility in untrained young adults. Land plyometrics

utilize body weight and gravity to eccentrically load the muscles. The elastic properties of

musculotendinous unit serve as store-houses of potential energy. The stretch reflex

provides a defense mechanism to protect against sudden, forceful muscular stretches. The

combination of the stretch reflex response and a maximal voluntary muscle contraction can

be very effective at improving muscle force generation. Although the stretch reflex and

the amount of eccentric loading are reduced in water by the effects of buoyancy, the

viscosity of the water provides greater than normal resistance (Martel et al, 2005). Thus,

the buoyancy of the water facilitates the concentric muscular component and decreases the

amortization phase of the plyometric task. Therefore, the aquatic group lands with a lower

12

load but have a faster transition time (Behm & Sale, 1993; Miller et al, 2002). This is

important for improving power. Whereas, the viscosity of the water tends to increase the

resistance to lateral movements and may be an important component in the improvement in

agility in the aquatic group.

Given that both the aquatic and land programs resulted in improvements in

strength, power, and agility, another consideration is the criteria for safe implementation of

a plyometric program. The National Strength and Conditioning Association

recommendation for implementation of a land plyometric program is the capacity to squat

150% of an individual’s weight for males and 75% for females (Potach & Chu, 2000).

These criteria would require significant lower extremity strength to accommodate the

shock absorption of these explosive, ballistic movements. However, when an individual is

submerged in water, he/she experiences a significant reduction in weight bearing. In

waist-high water, a person weighs 50% of the land weight. At chest-high water, a person

weighs 25% of the land weight. When submerged to the neck, an individual only weighs

10% of the land weight (Bates & Hanson, 1996). Thus, a person weighing 80 kilograms

on land would only need to squat 8-40 kilograms, depending on the level of submersion, to

safely participate in an aquatic plyometric program. This could be a significant advantage

to the athlete rehabilitating an injury. The buoyancy of the water would permit early

access to plyometrics and incorporation of sport-specific tasks. Likewise, many activities

of daily living have ballistic components to them. If incorporated into a therapeutic

exercise program, plyometric tasks in the water could enhance an individual’s tolerance to

these activities.

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In summary, the results of this study support the positive effects of aquatic

plyometrics with the added benefit of reduced joint compression forces (Prins & Havriluk,

1991; Rivera, 1994; Thein & Brody, 1998). Coaches, athletic trainers, and physical

therapists should be aware of these advantages when constructing a rehabilitation or

strength and conditioning program. Aquatic plyometrics should be considered as a

primary intervention technique as opposed to a substitute when an individual is unable to

perform land plyometrics.

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Table 1. Intervention and assessment sequence.

Week Sessions 1 Pre-test & Phase 1, session 1 & 2 2 Phase 1, session 3 & 4 3 Phase 1, session 5 & 6 4 Mid-test & Phase 2, session 1 & 2 5 Phase 2, session 3 & 4 6 Phase 2, session 5 & 6 7 Post-test

Table 2. Means ± Standard Error Group Time Strength (ft*lbs) Power (W) Agility (sec) Control Pre-test

Mid-test Post-test

63.86 ± 4.69 70.93 ± 5.32 73.87 ± 5.53

6777 ± 228 6912 ± 227 6913 ± 226

10.77 ± 0.33 10.65 ± 0.28 10.64 ± 0.25

Land Pre-test Mid-test Post-test

62.92 ± 3.71 69.42 ± 4.20 77.08 ± 4.37

7543 ± 180 7528 ± 179 7598 ± 179

10.69 ± 0.26 9.94 ± 0.22* 9.54 ± 0.20*

Aquatic Pre-test Mid-test Post-test

59.54 ± 3.71 71.27 ± 4.20* 77.73 ± 4.37*

7123 ± 180 7270 ± 179* 7292 ± 179

10.81 ± 0.26 10.04 ± 0.22* 9.69 ± 0.20*

* p< 0.05 Table 3. Summary of the analyses of variance for strength, power, and agility. Source SS df MS F p* Strength 3879.844 2 1938.422 23.074 0.000*Strength x Group 317.446 4 79.362 0.945 0.443 Power 215339.318 2 107669.659 4.441 0.015*Power x Group 113080.504 4 28270.126 1.166 0.332 Agility 13.435 2 6.717 20.760 0.000*Agility x Group 3.995 4 0.999 3.087 0.021**p < 0.05

19

Figure 1. Quadriceps strength testing position using a MicroFET handheld dynamometer.

20

Figure 2. Ricochets

21

Figure 3. Tuck jumps

22

Figure 4. High knee skips

23

Figure 5. Box drops

24

Figure 6. Ricochets over hurdles

25

Figure 7. Comparison of Strength for Control, Land, and Aquatic Groups

63.962.9

59.5

70.969.4

71.3

73.9

77.1 77.7

55

60

65

70

75

80

Foot

-Lbs

of F

orce

Pre-Test Mid-Test Post-Test

Time

Strength

Control

Land

Aquatic

26

Figure 8. Comparison of Power for Control, Land, and Aquatic Groups

6777

7543

7123

6912

7528

7270

6913

7598

7292

6500

6700

6900

7100

7300

7500

7700

Wat

ts

Pre-Test Mid-Test Post-Test

Time

PowerControlLandAquatic

27

Figure 9. Comparison of Agility for Control, Land, and Aquatic Groups

10.810.7

10.810.7

9.9

10

10.6

9.5

9.7

9.29.49.69.810

10.210.410.610.8

Seco

nds

Pre-Test Mid-Test Post-Test

Time

Agility

ControlLandAquatic

28