The Effect of Gastrocnemius Stretching on Hamstring Flexibility

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Effects of Gastrocnemius, Hamstring, and Combined Stretching Programs on Knee Extensibility Pamela J. Russell, PhD; Laura C. Decoster, ATC; and Darcie Enea, MEd

ABSTRACT sential. Athletes, coaches, and sports medicine clinicians This study examined the effectiveness of hamstrings-only, gas- widely accept and promote varied stretching routines trocnemius-only, and combined hamstrings-gastrocnemius to improve hamstring flexibility.1 Many investigations stretching on knee extensibility. The study also compared have tried to identify the ideal hamstring stretching rou- active knee extension (AKE) test outcomes for two positions: tine,2-17 but findings from a systematic literature review foot relaxed in plantar flexion (AKE-PF) and with ankle fixed in indicate that an ideal routine may not exist.1 Instead, a neutral (AKE-N). Forty-seven volunteer participants (94 legs) variety of stretching techniques (eg, ballistic, proprio- completed AKE-PF and AKE-N pretests. Forty-five of these par- ceptive neuromuscular facilitation, static), positions (eg, ticipants (89 legs) completed 12 stretching sessions (one 30- standing, seated, supine), and frequency and duration second stretch 3 times per week for 4 weeks) and an AKE-PF combinations successfully improve hamstring flexibil- posttest. Knee extensibility results showed no changes in the ity.1 More recent studies18-20 continue to reinforce these control group but similar and significant improvements in all findings, incorporating additional stretching techniques stretching groups, and significant reductions for the AKE-N test (eg, active controlled) and more varied positions (eg, compared with the AKE-PF test. Given these findings, clinicians supported lunge, seated in a chair). Clearly, a variety of should consider inclusion of gastrocnemius stretching in treat- effective stretching programs target and improve ham- ment plans designed to improve knee extensibility and moni- string flexibility, which increases knee extensibility. tor foot position during the AKE, perhaps using both plantar Sports medicine clinicians are typically well versed and dorsiflexed positions to gather more information regarding in the design of stretching programs, and some consider the sources of knee inextensibility. and treat gastrocnemius tautness when trying to improve knee extensibility and treat knee pathology.21 Human anatomical structure lends support to stretching the gas- he ability to extend the knee is critical to effective trocnemius and other posterior knee structures, but there sport participation and functional movements. is no known research evidence that demonstrates the ef- TWhen movements demand complete knee exten- fectiveness of gastrocnemius stretching in programs de- sion coupled with hip flexion, hamstring flexibility is -es signed to improve knee extensibility. Numerous studies show static hamstring stretching to improve knee extensibility.2,5-7,12,14,15,22 Given its posterior knee location, per- Dr Russell is from Movement Arts, Health Promotion & Leisure Studies Department, Adrian Tinsley Center, Bridgewater State College, Bridgewater, and haps simultaneously stretching both the gastrocnemius Ms Enea is from Plymouth North High School, Plymouth, Mass. Ms Decoster is and the hamstrings is the most effective way to increase from the New Hampshire Musculoskeletal Institute, Manchester, NH. Originally submitted August 5, 2009. knee extension range of motion. Accepted for publication November 2, 2009. The primary purpose of this study was to examine The authors have no financial or proprietary interest in the materials presented herein. the effectiveness of 3 different stretches on knee exten- Address correspondence to Pamela J. Russell, PhD, Movement Arts, Health sibility during a 4-week program. Of particular interest Promotion & Leisure Studies Department, Adrian Tinsley Center, Bridgewater State College, Bridgewater, MA 02325; e-mail: [email protected]. was the influence of the gastrocnemius. Hamstrings- doi:10.3928/19425864-20100226-06 only and combined hamstrings-gastrocnemius stretching

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protocols were expected to increase knee extensibility just the estimate of the standard deviation for hamstrings- as evidence shows increased knee extension with ham- only stretching (approximately 9°)25 and considering a 5° string stretching.6-8,10-12,15,16,19 The greatest improvements difference due to treatment clinically significant yields a in knee extensibility were expected with the combined power of 80%, with approximately 50 cases per treat- hamstrings-gastrocnemius stretch because it targets ment level (effect size of 0.24 for treatment differences more of the 2-joint muscles and structures that span the using a one-way analysis of variance).26 posterior knee. Conversely, the hamstrings-only and gastrocnemius-only stretches were expected to have Data Collection smaller effects on knee extensibility. Pretest. Participants arrived for AKE testing wearing A second goal of this study was to examine the in- shorts and a short sleeve top, having avoided strenuous fluence of foot position on the active knee extension exercise 12 hours prior. They removed their shoes and (AKE) test. The AKE test administration directions lay supine on a long, level and firm tabletop fitted with state that the ankle should remain relaxed in plantar a crosswire device, similar to that used by Gajdosik and flexion,23 yet clinical observations indicate that not all Lusin.23 (Note: Our crosswire device was a firm wire patients maintain this position without feedback. In suspended 10-12 inches above and across the tabletop. addition, controlled use of a neutral ankle or dorsi- Each end of the wire was attached to a post connected flexed foot position could provide information regard- to the table, allowing the participant to slide underneath ing additional sources of knee inflexibility. In a similar the wire while atop the table. Posts for the crosswire de- study of hamstring flexibility assessed by the straight vice are visible in Figures 1 through 3.) A test adminis- leg raise (SLR) test, significant decreases resulted from trator identified and marked the greater trochanter and fixing the foot in 10° of dorsiflexion.24 There is no lateral epicondyle of each femur with a black ink dot. known research evidence for the influence of foot po- Leg testing order (ie, right or left) was randomized us- sition on the AKE test. Thus, the second intent of this ing the software at http://www.randomizer.org. study was to determine the influence of a fixed neutral Figure 1 shows the start position for the AKE- ankle position on the AKE test outcome. The fixed PF test. The nontest leg was secured to the table at neutral ankle position elongates the gastrocnemius mid-thigh to restrain the tendency for pelvic tilt and and other posterior knee structures, so it was expected maintain a neutral pelvic position during the test. An to yield less knee extension than the ankle relaxed in adapted long-arm goniometer was attached to the test plantar flexion position. leg. To enhance measurement accuracy, 12-inch rulers were secured to each arm of this goniometer. Goniom- Methods eter placement put the axis over the dot on the greater trochanter and the distal end over the dot on the lateral Participants epicondyle of the femur. The proximal arm of the go- Forty-seven recreationally active college students (22 niometer was held parallel to the table top by the first men, 25 women; mean age, 21.562.4 years) volunteered test administrator (P.J.R.). The anterior thigh of the to participate. All participants provided consent on a form test leg barely contacted the crosswire device, yielding approved by the academic institutional review board. 90° of hip flexion on the goniometer. None of the participants was excluded when screened for To complete the AKE-PF test, participants slowly a history of orthopedic or neuromuscular dysfunction af- extended the knee, keeping the thigh in contact with the fecting flexibility and knee extensibility restriction ,20° crosswire and the ankle relaxed. Knee extension stopped assessed by the AKE test with the ankle relaxed in plantar when participants felt a strong, but not painful, pull in flexion (AKE-PF). Testing included both right and left the back of the leg or when the first test administrator legs, yielding a sample of 94 legs. Data collection and in- noted at least a 1° hip angle increase on the goniometer tervention activities occurred in the college’s biomechan- (indicating thigh movement away from the crosswire). ics laboratory. At the AKE-PF end position (Figure 2), the second test Sample size estimation was difficult, as the literature administrator (D.E.) placed a digital inclinometer on does not indicate variability associated with hamstrings- the lower leg to obtain its inclination angle in reference gastrocnemius or gastrocnemius-only stretching. Using to the horizontal. This inclinometer was calibrated to

1 2 Figure 1. Start position for assessment with ankle relaxed in plantar Figure 2. Measurement of maximum inclination angle during assess- flexion. ment with ankle relaxed in plantar flexion. the level tabletop before each testing session. The inclination angle was recorded and then converted to a posterior knee angle by adding 90°. Each participant repeated the AKE-PF test protocol on the other leg. Par- ticipant eligibility was based on restricted flexibility: the AKE-PF posterior knee angles had to demonstrate more than 20° of knee extension loss (<160° angle). AKE Test Foot Position Influence. Participants eligible for the intervention study had knee extensibility assessed a second time, 48 hours after the AKE-PF pretest 3 at approximately the same time of day (eg, late morning, Figure 3. Measurement of maximum inclination angle during assess- early afternoon, late afternoon). Participants completed ment with the ankle neutral. the same test protocol, but a lightweight heat-moldable splint was attached to the foot and lower leg to maintain string stretching in a supine position are comparable the ankle in neutral (AKE-N) (ie, at 90°) and prevent to gains from hamstring stretching in a standing posi- plantar flexion, which might allow for increased knee tion,3,27 and the supine position reduces the likelihood extensibility. At the end position (Figure 3), the lower of participants adopting a posterior pelvic tilt posi- leg inclination angle was used to calculate posterior tion, which might limit their stretching gains.15 There knee angle. was no research to guide selection of gastrocnemius- Posttest. After the intervention phase of the study, all only and combined hamstrings-gastrocnemius stretch participants completed their AKE-PF posttest within positions, so these stretches were based on common 48 hours of their last stretching session given that the clinical methods that used the same supine position positive effects of a flexibility program may begin to used in the hamstrings-only stretch. Static stretching diminish within 48 hours of program cessation.3,27 was selected because it poses little risk of injury3,27; Posttest procedures matched pretest procedures, with numerous studies show that static hamstring stretch- the same two test administrators performing the same ing improves flexibility.2,5-7,12,14,15,22 Thirty seconds of measurement tasks. The first administrator (who could stretch is an effective duration,2 and the completion stop the test due to hip angle changes) was blinded to of 1 repetition per day 3 times per week for 4 weeks intervention group assignment until the completion of (ie, 12 sessions) is well within the range of frequency all posttests. protocols that increase flexibility.3,27 Stretching groups maintained their current activity level but added one Interventions 30-second repetition of the assigned stretch to each leg The selection of the hamstrings-only stretch position 3 times per week for 4 weeks. The control group kept was based on previous research.3 Gains from ham- their activity level consistent for 4 weeks.

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4 Figure 4. Gastrocnemius-only endpoint stretch position. 5 Figure 5. Hamstrings-only endpoint stretch position.

sliding the entire torso closer to, or farther from, the wall to create the stretch sensation in the back of the thigh. The combined hamstrings-gastrocnemius stretch (Figure 6) group added a gastrocnemius stretch to the hamstrings-only stretch. Participants adjusted torso position first to create the stretch in the back of the thigh, 6 and then both hands evenly pulled on a nonelastic strap Figure 6. Hamstrings-gastrocnemius endpoint stretch position. to create an additional stretch sensation behind the knee, in the upper calf, or in both places. Immediately following the AKE-N test, partici- Each week, the stretching group participants visited pants were randomly assigned to one of four groups: the laboratory for supervision of 1 of their 3 stretching control, gastrocnemius-only stretching, hamstrings- sessions and to report the other days and times during only stretching, or combined hamstrings-gastrocne- the week when they had stretched. The second test ad- mius stretching. Software at http://www.randomizer. ministrator coordinated all stretching-related activities org was used for random assignment to groups. Each (ie, group assignment, demonstration, supervision and participant received a demonstration of the assigned compliance recordkeeping) to keep the first test admin- stretch and a handout with directions and a picture of istrator (who could stop the AKE posttest) blinded to all the endpoint position. Participants then performed the stretching activities. stretch under the supervision of the second test administrator. Design and Statistical Analysis Directions common to all of the stretches included: A pretest-posttest design with a control group was used Relax your head, neck, and trunk on the floor; posi- to examine the effect of 3 different stretches on knee ex- tion yourself to feel a strong, but not painful, stretching tensibility as assessed with the AKE-PF test. An analysis sensation; and hold the stretch for a timed 30 seconds, of covariance (ANCOVA) determined the effects of the then repeat it on the other leg. stretching intervention on the AKE-PF posttest pos- The gastrocnemius-only stretch (Figure 4) group used an terior knee angle across the 4 groups. AKE-PF pretest even pull with both hands on a nonelastic strap to move posterior knee angles served as the covariate to equalize the ball of the foot toward the head, without hip or knee any influences across the groups due to pretesting. A flexion, to create the sensation of stretch behind the knee, paired samples t test compared AKE-PF and AKE-N in the upper calf, or in both places. posterior knee angles to determine the influence of foot The hamstrings-only stretch (Figure 5) group position on the AKE assessment. All statistical analyses kept the foot of the leg being stretched relaxed in used SPSS version 16 software (SPSS Inc, Chicago, Ill), plantar flexion while adjusting stretch intensity by with significance set atP , .05.

Table Comparisons of Control and Stretching Groups 95% Confidence Pretest Posterior Posttest Posterior Significance from Difference Intervals Group Knee Angle (°)a Knee Angle (°)b Control (P)c (Pairwise comparisons) Control (n = 28) 101.25 (2.51) 104.2 (2.25) Gastrocnemius (n = 16) 103.94 (3.24) 116.1 (2.96) .012 –1.86 to –21.96 Hamstrings (n = 23) 101.22 (2.25) 115.0 (2.48) .010 –1.81 to –19.81 Combined hamstrings- 107.73 (2.45) 117.6 (2.57) .001 –4.08 to –22.66 gastrocnemius (n = 22) a Covariate: Pretest knee angle used for evaluation = 103.33°. b Posttest knee angles adjusted for the use of the covariate. c Adjusted for multiple comparisons with Bonferroni.

Results in this study (ie, one 30-second repetition 3 times per Forty-seven participants (94 legs) completed the inter- week for 4 weeks) is well within the duration and fre- vention part of the study, but 2 participants (4 legs) were quency range of successful stretching programs.1 For disqualified for missing 2 stretching sessions within example, one 60-second static stretch once per week 1 week. Forty-five participants (90 legs) completed all for 3 weeks significantly increased (mean = 5.7°) knee 12 stretching sessions, with 6 of these participants com- extensibility.3,27 At the other extreme, 5 repetitions of pleting their twelfth session early in the fifth week. One a 30-second static stretch 3 times per week for 8 weeks leg was excluded from posttesting because it recently also significantly increased knee extensibility (mean = sustained an ankle sprain, yielding a sample of 89 legs. 11.2°).3,27 Thus, a stretching program that incorporates ANCOVA results indicated that stretching signifi- one 30-second repetition of the investigated stretches cantly improved knee extensibility (F3,84 = 6.64, P , .0001, 3 times per week for 4 weeks has potential to increase observed power = 0.968). Pairwise comparisons revealed knee extensibility. that all stretching groups differed from the control group Unexpectedly, there were no statistically significant at varying levels of significance (Table). The combined differences among the stretching groups. All partici- hamstrings-gastrocnemius group was most different from pants had enough posterior leg flexibility loss that each the control group, with the 95% confidence interval for stretching program improved knee extensibility. This differences ranging from 4.08° to 22.66° (P , .001). None finding supports clinical consideration of stretching just of the stretching groups differed from each other. the gastrocnemius to increase knee extensibility. Others Forty-seven participants (94 legs) completed the have not investigated the influence of gastrocnemius- AKE-PF and AKE-N tests. Results of a 2-tailed paired only stretching on knee extensibility, but gastrocnemius samples t test indicated significantly t( 93 = 5.085; P , .001) stretching is known to benefit the range of available dor- greater knee extensibility (102.95°612.67) with the AKE- siflexion.28,29 Increased knee extensibility with gastrocne- PF test compared with the AKE-N test (96.97°611.53). mius stretching is most likely due to the posterior loca- The 95% confidence interval of mean differences spanned tion of the gastrocnemius, spanning the knee and ankle. 3.64° to 8.31°. Stretching this 2-joint muscle will decrease tautness for the entire muscle, as opposed to its crossing at a single Discussion joint, allowing gastrocnemius tautness to influence knee The primary goal of this study was to examine the ef- extensibility. For this sample of healthy college-aged par- fectiveness of 3 different stretches on knee extensibility ticipants, gastrocnemius stretching alone was equivalent during a 4-week period. The influence of the gastrocne- to hamstring stretching alone and combined hamstring mius was of particular interest. Statistically, all 3 stretch- and gastrocnemius stretching for improving knee exten- ing programs significantly improved knee extensibility sibility as determined by the AKE-PF test. as determined by the AKE-PF test. This finding was not Ninety-five percent confidence intervals (Table) -in surprising, as the volume of static stretching completed dicated that the combined hamstrings-gastrocnemius

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group had the largest minimum difference (4.08°) com- provide additional information about knee flexibility24 pared with the control group. This minimum difference and help clinicians design interventions to address knee (4.08°) is higher than the minimums of the 95% confi- pathology. dence intervals for the gastrocnemius-only (1.86°) and hamstrings-only (1.81°) stretching groups. A 4° mini- Limitations mum may approach clinical relevance. These findings Use of healthy college-aged participants in this study highlight the need for further investigation to determine limits generalization to individuals with injured lower combined hamstrings-gastrocnemius effectiveness, extremity tissues. Observed power of findings was compared with other stretches designed to improve strong, but an appropriate sample size was difficult to knee extensibility. Combined hamstrings-gastrocne- estimate given lack of published data for gastrocnemius- mius group changes were statistically the same as the only and combined hamstrings-gastrocnemius stretch- other stretching groups, but using a single stretch to tar- ing routines; thus, 95% confidence interval ranges get more of the 2-joint muscles that span the posterior should be examined to discern the clinical relevance of knee may be an efficient way to create reliable and clini- findings. Hip flexor and gastrocnemius tautness were cally significant increases in knee extensibility. not assessed, but random assignment of participants to The secondary purpose of this study was to deter- groups should have randomly distributed any potential mine the influence of a fixed neutral ankle position on influence of preexisting hip flexor or gastrocnemius the AKE test. Results indicated a significant mean de- tautness on the findings. Restraint of the nontest leg crease of 6° in knee extension with the ankle neutral as was also incorporated to minimize the influence of hip- opposed to relaxed in plantar flexion. These findings are flexor tautness by inhibiting pelvic tilt. Future studies similar to those of Gajdosik et al,24 who assessed ham- should assess hamstring and gastrocnemius flexibility string flexibility with the SLR (n = 22) comparing fixed independently to further the understanding of com- dorsiflexion with relaxed plantar flexion positions. Ten bined hamstrings-gastrocnemius and gastrocnemius- degrees of fixed dorsiflexion decreased knee extension only stretching on knee extensibility. Improved un- in both active (9.1°67.5°) and passive (10.1°65.1°) ver- derstanding of protocols that use these stretches could sions of the SLR.24 Use of a fixed ankle neutral position facilitate matching the most effective knee extensibility in this study, as opposed to 10° of fixed dorsiflexion, program to specific patient populations. could have narrowed the difference between the AKE- N and AKE-PF conditions. Forced dorsiflexion may Conclusion decrease knee extension because it increases the resting AKE-PF test results indicated significant knee exten- tension of posterior knee structures that also span the sibility increases in healthy college-aged participants ankle, such as the sciatic nerve,30 gastrocnemius, skin, when stretching the gastrocnemius only, the hamstrings and subcutaneous connective tissues.24 A neutral ankle only, or simultaneously stretching the hamstrings and position may also increase the tension in these struc- gastrocnemius during a 4-week program that required tures. Increased resting tension in the posterior ana- one 30-second stretch 3 times per week. Findings also tomical structures distal to the knee decreases the active demonstrated decreased knee extensibility with com- range of knee extension, reemphasizing the need to pletion of the AKE test with the ankle in neutral, as op- standardize the test procedure24 and monitor foot posi- posed to relaxed in plantar flexion. Given these results, tion during test completion. clinicians should consider the inclusion of gastrocne- Using both plantar and dorsiflexed foot positions in mius stretching in treatment plans designed to improve the AKE test might provide clinicians with more infor- knee extensibility and monitor foot position during the mation about the influence of 2-joint posterior knee and AKE, perhaps using both plantar and dorsiflexed posi- ankle structure tautness on knee extensibility. This in- tions to gather more information regarding the sources formation could be useful in designing patient-specific of knee inextensibility. n rehabilitation protocols, such as those for patients who participate in closed chain activities where knee exten- References sion occurs from a dorsiflexed foot position. Com- 1. Decoster LC, Cleland J, Altieri C, Russell P. The effects of hamstring parison of test results from both foot positions could stretching on range of motion: A systematic literature review. J Or-

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