2011 immediate effects of quantified hamstring stretching, hold-relax proprioceptive neuromuscular...

8/9/2019 2011 Immediate Effects of Quantified Hamstring Stretching, Hold-relax Proprioceptive Neuromuscular Facilitation Versus Static Stretching (1)

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Original research

Immediate effects of quanti ed hamstring stretching: Hold-relax proprioceptiveneuromuscular facilitation versus static stretching

Emilio J. Puentedu ra a , * , Peter A. Huijbregts b , Shell ey Celeste a, Dale Edwards a, Alastair In a,Merrill R. Landers a, Cesar Fernandez-de-las-Penas c

a Department of Physical Therapy, School of Allied Health Sciences, University of Nevada Las Vegas, Las Vegas, NV, USAb In memorium, Shelbourne Physiotherapy Clinic, Victoria, British Columbia, Canadac Department of Physiotherapy, Occupational Therapy, Rehabilitation and Physical Medicine, Universidad Rey Juan Carlos, Alcorcon, Madrid, Spain

a r t i c l e i n f o

Article history:Received 14 September 2010Received in revised form16 February 2011Accepted 21 February 2011

Keywords:ExerciseHumansMuscleSkeletal/physiologyRange of motion

a b s t r a c t

Purpose: To compare the immediate effects of a hold-relax proprioceptive neuromuscular facilitationstretching (HR-PNF) versus static stretch (SS) on hamstring exibility in healthy, asymptomatic subjects.Subjects: Thirty subjects (13 female; mean age 25.7 3.0, range 22 e 37) without excessive hamstringmuscle exibility were randomly assigned to one of two stretch groups: HR-PNF or SS.Methods: The left leg was treated as a control and did not receive any intervention. The right leg wasmeasured for ROM pre- and post-stretch interventions, with subjects receiving randomly assignedinterventions one week apart. Data were analyzed with a 3 (intervention: HR-PNF, SS, control) 2 (time:pre and post) factorial ANOVA with repeated measures and appropriate post-hoc analyses.Results: A signi cant interaction was observed between intervention and time for hamstring extensi-bility, F (2,58) ¼ 25.229, p < .0005. Main effect of intervention for the tested leg was not signi cant, p ¼ .782 indicating that there was no difference between the two stretch conditions. However, maineffect for time was signi cant ( p < .0005), suggesting that hamstring extensibility (for both stretchingconditions) after intervention was greater than before.Conclusion: No signi cant differences were found when comparing the effectiveness of HR-PNF and SStechniques. Both stretching methods resulted in signi cant immediate increases in hamstring length.

2011 Elsevier Ltd. All rights reserved.

1. Introduction

Hamstring strains are a common occurrence in many athleticendeavors including sprinting, martial arts, water skiing, dance,soccer, rugby, and all forms of football ( Bahr & Holme, 2003 ). Witha seasonal incidence of 5.5 e 6.7% hamstring strains are the mostfrequent of all injuries in Australian Rules football ( Orchard &Seward, 2002 ). Hamstring strains accounted for 11% of injuries inBritish professional soccer and for 12.7% in the two highest soccerdivisions in Iceland ( Arnason, Sigurdsson, Gudmundsson, Holme,Engebretsen, Bahr, 2004; Dadebo, White, & George, 2004 ). Ina study of student e professional dancers in Sweden, researchersfound 51% career prevalence for hamstring injuries ( Askling, Lund,Saartok, & Thorstensson, 2002 ). Also, at 34% in Australian Rulesfootball and 14% in British professional soccer, reported recurrencerate is high ( Dadebo et al., 2004; Orchard & Seward, 2002 ).

Hamstring stretching may be considered as an intervention inboth prevention and treatment of hamstring strains. Althoughstretching with the intent of injury prevention is common practicein many sports ( Witvrouw, Mahieu, Danneels, & McNair, 2004 ),evidence for decreased hamstring exibility as a risk factor forhamstring strain remains equivocal ( Hennessey & Watson, 1993;Witvrouw, Danneels, Asselman, D ’ Have, & Cambier, 2003 ) anda recent Cochrane review found no evidence for stretching as a soleintervention for prevention of hamstring injury ( Goldman & Jones,2010 ). Hamstring exibility has been suggested as but one factor inthe multi-factorial etiology of hamstring strain injury ( Worrell &Perrin, 1992 ). In a review on risk factors for recurrent hamstringstrains, Croisier (2004) noted limited evidence for stretching butsuggested at least normalizing hamstring length. Witvrouw et al.(2004) suggested that stretching might be most relevant forsports that predominantly include plyometric activities. Ina Cochrane review, Mason, Dickens, and Vail (2007) reportedevidence for a higher frequency of daily stretching in the rehabili-tation of hamstring injuries.

Stretching has been classi ed into static, dynamic, ballistic, andproprioceptive neuromuscular facilitation (PNF) techniques

* Corresponding author. Tel.: þ 1 702 895 1621; fax: þ 1 702 895 4883.E-mail address: [email protected] (E.J. Puentedura).

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Physical Therapy in Sport

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1466-853X/$ e see front matter 2011 Elsevier Ltd. All rights reserved.

doi: 10.1016/j.ptsp.2011.02.006

Physical Therapy in Sport 12 (2011) 122 e 126

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(Knudson, 1998 ). PNF techniques are based on the work by Voss,Ionta, and Myers (1985) and include a hold-relax technique thatinvolves lengthening the muscle to the point of limitation, at whichpoint the individual performs an isometric contraction for up to10 s, followed by a passive movement of the limb into the new end-range. Static stretching takes the muscle to its end-range and this isheld in thisposition foran extendedperiod of time with a sustainedforce. In a systematic review of the literature, Decoster, Cleland,Altieri, and Russell (2005) suggested that all hamstring stretchingtechniques cause at least a temporary increase in range but alsothat the literature on direct comparisons between differentstretching techniques is limited and of low methodological quality,making it dif cult to determine which technique is most effective.The purpose of the current paper, therefore, is to compare theimmediate effects of a hold-relax PNF (HR-PNF) and a static stretch(SS) on hamstring exibility in a healthy, asymptomatic populationbut controlling for some relevant confounders present in previousstudies.

2. Methods and materials

2.1. Subjects

We recruited a convenience sample of 30 subjects (13 female;mean age 25.7 3.0, range 22 e 37) who were students and facultyfrom a local university. Exclusion criteria were (possible) preg-nancy, hamstring injury within the past year, exceeding 80 in theinitial active knee extension (AKE) test, and/or participation insports that required regular hamstring stretching. Based on thesecriteria no subjects were excluded.

2.2. Measurement of hamstring exibility

The AKE test has been recommended as an alternative to thestraight-leg raise test because it eliminates the pelvic rotation thatoccurs with the latter test ( Sullivan, Dejulia, & Worrell, 1992 ). Thesubject was supine with both the hip and knee positioned in 90 of

exion and was then asked to actively extend the lower leg until thepoint of limitation; hip exion was maintained with the use of a stationary board on the distal thigh ( Fig. 1). The subject ’ s AKEmeasurement was recorded three times using an Acumar (ACU360) digital inclinometer (Lafayette Instrument Co., Lafayette, IN)placed over a marked position on subject ’ s anterior leg at the tibialtuberosity. The examiner holding the inclinometer was blindedfrom the measurements of the AKE test by positioning the

inclinometer ’ s digital window away from the examiner, whileanother researcher read and recorded the results as an average of the three measurements. Within-session intra-rater reliability wasestablished on the rst 10 subjects as suf cient for clinicalmeasurement (ICC ¼ .96); although less relevant to calculation of responsiveness data and subsequent interpretation of the study

ndings, between-session intra-rater reliability was similarlyestablished as suf cient (ICC ¼ .94).

2.3. Stretching intervention

Subjects were supine on a treatment table secured underneatha pulley system constructed speci cally for this study. A nylon ropewas attached to the subject ’ s ankle via a metal hookto a laced anklebrace that also kept the ankle and foot in a neutral position. Thisrope passed through a rst pulley on the overhead frame that wasadjustable to allow for a stretching force perpendicular to the lowerleg, then a second stationary pulley, and nally down to a metalapparatus that suspended the free weights ( Fig. 2).

To standardize stretching torque proportional to 5% of subjectbody mass, the amount of free weight to be applied for each subjectwas calculated based on the tibial lever arm length and force loss inthepulley system.Admittedly,the choice of 5% wasarbitraryand ourmain concern was not magnitude but rather standardization of theload.However,with subjects indicatinga meandiscomfort rating ona 0 e 10 scale of 8.29 for HR-PNF and 8.06 for SS interventions at the5% load, ourarbitrary choice seemed fortuitous in that a higher loadwould likely have led to unacceptable discomfort ratings possiblyconfounding study outcomes. In a pilot study, a mechanical dyna-mometer measured actual force exerted through the pulley system(Y) with various weights applied to the pulley system (X) anda linear conversion factor was calculated ( Y ¼ 2.262 þ .811X) todetermine the weight required to correct for force lost within thepulley system. With body weightrangingfrom 48.4 to 113.7(kg) andtibial length between 34.1 and 47.5 (cm) weights applied at thedistal end of the pulley system averaged 17% (range 13 e 30%) of subject body weight.

The left (control) leg was secured to the plinth with the hip andknee in neutral, using a Velcro belt across the inferior thigh andover the anterior superior iliac spine; only the right leg wasstretched. A McKenzie lumbar roll was placed under the subject ’ slower back during both stretching interventions to maintain ananterior pelvic tilt during the stretch ( Sullivan et al., 1992 ). Duringstatic stretching, two 30-s stretches were applied by the suspendedweights, with each stretch followed by 10 s of rest. During HR-PNF

Fig. 1. During the AKE test, the subjects ’ femur maintained contact with the horizontal board to keep the hip in 90 of hip exion, and a mark was made on the tibial crest,10 (cm)distal to the tibial plateau, for placement of the digital inclinometer (left). The examiner holding the inclinometer was blinded from the measurements of the AKE test by positioning

the inclinometer’

s digital window away from the examiner, while another researcher read and recorded the results as an average of the three measurements (right).

E.J. Puentedura et al. / Physical Therapy in Sport 12 (2011) 122 e 126 123



stretching, the examiner lengthened the hamstring muscle to endrange, after which the subject performed a 10-s maximal isometriccontraction against the examiner ’ s resistance, followed by 10 s of passive stretch by the pulley system. Four repetitions were done tomatch the SS intervention total duration of 80 s. Although werecognize that 60 s of SS with 20 s of rest does not equal the totalstretching duration of 40 s of HR-PNF with 40 s of maximalisometric contraction, we note that research does not identify the“ active ” component of either intervention responsible for musclelength increases. In absence of this knowledge, we decided tostandardize the stretch duration as discussed above.

2.4. Procedures

This study was approved by the Institutional Review Board of the University of Nevada Las Vegas. Subjects signed a consent formand agreed to participate in two testing sessions separated by oneweek. Using a random numbers table, subjects were randomlyassigned to receive either the static or HR-PNF stretch on the rstday and then given the other stretch technique the following week.The subjects changed into loose shorts, removed their shoes, andwere weighed. One examiner marked the medial joint line of theknee just above the medial tibial plateau and measured thedistance from the medial joint line of the knee to the medial mal-leolus of the ankle to determine tibial lever arm length. A mark wasmade on the tibial crest, 10 (cm) distal to the tibial plateau, forplacement of the digital inclinometer. The subjects then rodea stationary bike for 5 min maintaining 70 rpm at a set resistancesimilar for all subjects to ensure that pre-stretching parameterswere consistent among subjects. De Wijer et al. (2003) showed thata warm-up prior to stretching did not affect the effectiveness of thestretch.

The AKE test was measured three times in the control (left) legrst and then repeated on the subject ’ s test (right) leg. No lumbar

roll was used during the AKE at pre-test and post-test. After thesubject ’ s leg was attached to the pulley system, one researcheradjusted the angle of pull on the tibia as close as possible toperpendicular. Stretch instructions were given to the subjectthrough speci c verbal commands and durations were monitoredusing a stopwatch. The particular assigned stretching techniquewas then administered to the subject by the examiners. A post-testAKE measurement was then obtained 30 s post-stretch using thesame protocol as at pre-test.

2.5. Statistical analysis

Descriptive statistics (mean, standard deviation, 95% CI) werecalculated for pre-test and post-test AKE averaged values for thetreated and untreated legs. AKE responsiveness data were calcu-lated using the within-session ICC established in this study(ICC ¼ .96) and the formulae SEM ¼ SD O(1 ICC) (Weir, 2005 )and MDC 95 ¼ 1.96 O2 SEM (Stratford, 2004 ). In order to assess

the relationship of the type of stretching on hamstring extensibility,one 3 (intervention: HR-PNF, SS, control) 2 (time: pre and post)factorial ANOVA with repeated measures on both factors wasconducted, with appropriate post-hoc analysis. Signi cance levelwas set at .05. A Bonferroni corrected alpha of .01 would be utilizedfor simple main effects analyses.

3. Results

Descriptive statistics are providedin Table 1 . Standarddeviationsfor AKE measurements ranged from 7.67 to 10.49 ( Table 1 ). Thisallowed us to calculate a range of SEM from 1.5 to 2.1 and subse-quently a range for the MDC 95 of 4.2 e 5.8 . The pre-test-to-post-test

differences in averageAKE values( Table1 ) exceededthe upperlimitof this MDC 95 range both for the HR-PNF (8.9 ) and SS (9.1 ) inter-ventions in the treated leg but not for the control leg (1.5 ).

A statistically signi cant interaction was observed,F (2,58) ¼ 25.229, p < .0005, h p

2 ¼ .465( Fig.3).Inordertobreakdownthe interaction 5 simple main effects tests were conducted. Therewas no signi cant difference among the groups before treatment, p ¼ .123. However, there was a signi cant difference after thetreatment, p < .0005. Pairwise comparisons revealed a signi cantdifference between the HR-PNF condition and the control condition( p < .0005) and between the SS condition and the control condition( p ¼ .011). There was no difference between the two stretchingconditions, p ¼ .782 (Cohen ’ s d ¼ .165; power ¼ .199). In order todetermine if each of the three conditions improved signi cantlyfrom thepre measurement tothe post measurement,threepaired t -tests were conducted. Both of the stretching conditions increasedAKEsigni cantly over time,ps < .0005.Thecontrolcondition didnotchange over time, p ¼ .163.

Table 1Descriptive statistics.

Intervention Time Mean ( ) Difference betweenpre and post

Standard deviation 95% Con dence Intervals

Lower Bound Upper Bound

HR-PNF Pre 57.63 8.9 7.67 54.77 60.50Post 66.51 7.88 63.57 69.45

SS Pre 56.05 9.1 8.93 52.71 59.39Post 65.18 8.22 62.11 68.25

Control Pre 58.34 1.5 9.28 54.88 61.80Post 59.79 10.49 55.88 63.71

Fig. 2. The custom-made pulley system consisting of 2 overhead pulleys and a treat-ment table. The static stretch was applied through the pulley system as shown.




4. Discussion

The results from this study showed no signi cant between-group difference favoring either HR-PNF or SS techniques withregard to increasing immediate post-intervention hamstring exi-bility. However, both stretching interventions did produce statis-tically signi cant increases in hamstring exibility compared tobaseline AKE values in both the treated and untreated legs. Withpre-test-to-post-test differences in average AKE values exceedingthe MDC 95 for both interventions in the treated but not in thecontrol leg, we suggest that changes observed in the control legwere likely the result of measurement error and do not representa true change in hamstring exibility.

Previous studies have compared various forms of PNF to SS

interventions to increase hamstring exibility using stretchinginterventions performed over multiple weeks. Prentice (1983)showed signi cant increases in hip exibility for 10 weeks of slow-reversal-hold PNF techniques over an SS intervention. Davis,Ashby, McCale, McQuain, and Wine (2005) showed a signi cantincrease in hamstring exibility only after 4 weeks of SS but notwith agonist contract-hold PNF intervention. In contrast, Sullivanet al. (1992) found no signi cant between-group differences inhamstring exibility after 2 weeks of either SS or antagonistcontract-hold-agonist contract PNF intervention. Worrell, Smith,and Winegardner (1994) even noted no signi cant pre-test-to-post-test within-group changes in hamstring exibility after threeweeks of using the same interventions in either group.

To our knowledge only two previous studies have compared SS

and HR-PNF interventions. Medeiros, Smidt, Burmeister, andSoderberg (1977) found signi cant immediate pre-test-to-post-test changes in passive hip exion for both intervention groups overa control group but no signi cant between-group differencesfavoring either intervention. Gribble, Guskiewicz, Prentice, andShields (1999) found signi cant within-group changes for eithergroup after 6 weeks of stretching but no between-group differencesin hamstring exibility. The current study adds further evidence toindicate that there is no difference in immediate post-interventioneffectivenessbetweenbothinterventions. However, the comparisonbetween the two treatment interventions was clearly narrow(Cohen ’ s d ¼ .165) and underpowered (power ¼ .199). In light of our

ndings, wecalculated thenumberof subjectsthat wouldhavebeenneeded to detect a signi cant difference. Considering a modest

power of 70%, the estimated number of subjects needed to see

a difference between these two stretching interventions would be236 on the low end and 942 on the high end. This would have beenimpractical in most research settings. Consequently, we feel that itwould be easier and more practical to instruct the patient in SSrather than HR-PNF. Because they do not require therapist assis-tance, static techniques would seem a more appropriate interven-tion than HR-PNF for increasing hamstring exibility.

The current study addressed a number of relevant confounderspresent in previous studies comparing PNF and SS interventions.We standardized stretching torque proportional to body mass andprovided equal stretching torque and duration in both interven-tions. Blinding the examiner to inclinometer readings removeda further potential bias ( Decoster et al., 2005 ). Sullivan et al. (1992)illustrated the importance of pelvic position during hamstringstretching; therefore, we controlled pelvic position using a lumbarroll and xation of the control leg. However, we also need toacknowledge some limitations to this study. The control conditionin the study was not a true control by strict de nition. The twostretching conditions were applied to one leg, while the “ pseudo ”

control was the contralateral leg. This limitation is mitigated by thefact that the control condition was still the same person. In addi-tion, there was no signi cant difference among the AKE values atthe pre-test. As with all other studies comparing PNF and SS weused relatively young asymptomatic subjects and ndings cannotbe readily extrapolated to older, symptomatic subjects. Collectingimmediate post-test data precludes making longer-term conclu-sions. Finally, including subjects with at times only minimalrestriction on the AKE test (AKE 80 ) may have introduceda ceiling effect.

5. Conclusion

The current study showed no bene t of SS over HR-PNF inter-ventions or vice versa with regard to increasing hamstring exi-bility. This nding controlled for a number of potential confoundersnot addressed in previous studies. Still, its ndings are fullyconsistent with these previous studies and indicate that whenchoosing between SS and HR-PNF interventions for the manage-ment of decreased hamstring exibility, therapists should basetheir approach on factors such as ease of instruction and require-ments for therapist assistance rather than on assumptions of rela-tive effectiveness.

Con ict of interest None declared.

Ethical approvalThis clinical trial received full board approval from UNLV Of ce

for the Protection of Human Research Subjects (Protocol # 0703-2309).

Funding None declared.

Acknowledgments

The authors would like to acknowledge the following peoplewho assisted in this study: Ty Druse, PT, DPT, LAT, ATC and HarveyWallmann, PT, DSc, SCS, LAT, ATC, CSCS.

It is with great sadness that we say good-bye to our close friendand colleague Peter Huijbregts, who tragically passed away onNovember 6th 2010. Peter made many terri c contributions to theprofession of physical therapy. He had a terri c passion for life andwas truly an inspiring individual who will be greatly missed by us

and the profession.

Fig. 3. Mean AKE values ( ) with standard deviation of hamstring extensibility of treated leg before and after HR-PNF and SS.




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