Effect of Cessation and Resumption of Static Hamstring Muscle ~tretihin~ on Joint Range of Motion

Journal of Orthopaedic & Sports Physical Therapy 2001;31(3): 138-144 Effect of Cessation and Resumption of Static Hamstring Muscle ~tretihin~ on Joint Range of Motion Richard W Willy, MPT1 Bryan A. Kyle, MPT1 Shawn A. Moore, MPT1 Gary S. Chleboun, PhD, PTZ Journal of Orthopaedic & Sports Physical Therapy Study Design: Single group repeated measures. Objectives: To determine the effects of cessation and resumption of a hamstring muscle stretching protocol on knee range of motion (ROM). Background: It is generally accepted that stretching exercises result in an increase in ROM. The ability to maintain ROM once stretching has ceased and the ability to regain ROM after resumption of the stretching exercise is not well-known. Methods and Measures: Evaluated the effect of 6 weeks of static hamstring stretching, 4 weeks with cessation from stretching, and 6 weeks with resumption of stretching on knee ROM in 18 inactive college students (12 men, 6 women, mean age 21.0 years). The hamstring stretching consisted of 2 30-second stretches per day, 5 days per week. Knee ROM was measured before and after each of the above phases with an active knee extension test. Results: Mean knee ROM increased after the initial stretching period (1 43 + 1 1" to 152 + go), decreased to baseline following the cessation period (145 t 8") and again increased following the resumption of stretching but was not different from the initial gains (154 + 10"). Unlike the stretch limb, the control limb ROM did not change over the 4 measurement times. Conclusions: There was no retention of knee ROM 4 weeks following a 6-week stretching protocol and a subsequent stretching period did not enhance the gain of knee ROM over the initial stretching period. ) Orthop Sports Phys Ther 2001;31:138-144. Key Words: muscle flexibility, rehabilitation At the time of this study, a student at the School of Physical Therapy, Ohio University, Athens, Ohio. Associate professor, School of Physical Therapy, Ohio University, Athens, Ohio. This study was approved by the Ohio University institutional Review Board. Send correspondence to: Gary S. Chleboun, School of Physical Therapy, 172 Convocation Center, Ohio University, Athens, OH 45701. E-mail: chlelwun@ohio.edu S tatic muscle stretching is a foundation for therapeutic exercise programs for recreational or competitive athletes and patients in rehabilitation. Benefits derived from stretching may include gains in range of motion (ROM), decreased muscle soreness, and decreased injury pre~alence.~.~j~ Much of the current research has focused on the proposed mechanisms of these benefits which include potential increases in musculotendinous length, increased stretch tolerance, alteration of muscle stiffness, and viscoelastic stress relaxa- ~on.3.6.7.11l16.22-24 Static stretching consists of a sustained elongation of the desired muscle group, with a duration of 15-120 second^.^ Increased ROM has been observed both at the time of a single episode of stretching and after several weeks of stretching. An increase in maximal joint ROM occurs during a single episode of the static stretch and for a short time period after the completion of a single stret~h.~j~j~ Proposed mechanisms behind these gains in maximal joint ROM include viscoelastic

stress relaxationi3 and an increased tolerance to stretch.'." Changes in maximal joint ROM also occur after several weeks of performing stretching exercise~.~-~.~.~~ The specific duration, frequency, and number of repetitions varies considerably among the studies cited. The differences in static stretching methodology mirrors the differences in stretching exercise prescription in rehabilitation programs among clinicians. Nevertheless, it has been demonstrated that a 30-second hamstring stretch performed once a day is sufficient to increase knee joint ROM.Is2 Proposed mechanisms for the benefits derived from static stretching over several weeks include an actual increase in musculotendinous length and an increased tolerance to stretch. A client who has a musculotendinous injury will typically be given a home exercise program with strengthening or stretching exercises. Once the client is discharged from therapy, the rate of continued compliance with the home exercise program has been found to be as low as 35%.19 Evidently, the majority of exclients do not continue their home exercise program after discharge. Therefore, the degree of retention of rehabilitation program benefits, both in strength and stretching gains, is of great interest. Although retention of strength benefits following cessation of a strength training program has been demon~trated?~~ it is unclear whether similar results occur when a stretching program is discontinued. To our knowledge, only 2 studies have addressed whether gains in ROM are retained after a period of stretching. Wallin and colleagues25 determined the amount of stretching that was needed to maintain the ROM that was gained in an initial stretching pre gram. They found that after 30 days of a contractrelax stretching program, once a week of contractrelax stretching was sufficient to maintain the benefits of the initial stretching period.25 Range of motion continued to improve after the initial stretching period if the contract-relax stretching was done 3 and 5 times per week. They did not, however, address the retention of ROM if the stretching is completely stopped. Zebas and Rivera26 did address this issue directly; they evaluated the effects of a &week flexibility program on ankle, hip, trunk, shoulder, and neck ROM. Subjects were divided into ballistic, proprioceptive neuromuscular facilitation (PNF), and static stretching groups. Range of motion was evaluated at the conclusion of the &week training period and at 2 and 4 weeks following cessation of the stretching regimen. Ballistic, PNF, and static stretching techniques demonstrated similar ROM gains following stretching. Following the cessation period, the static- and PNF-trained groups showed a significant retention of ROM, but ROM returned to baseline for the ballistic-trained However, the stretching protocols (intensity and duration of stretch and spe- cific stretching exercises) and the methods utilized for measurement of ROM were not well delineated. Despite the results presented by Zebas and RiveraF6 clinical observation suggests that patients who stop a stretching program lose ROM. Due to the previously noted low rate of continued patient compliance with a home exercise program after discharge from a rehabilitation program, retention of the benefits of a muscle-stretching program deserves additional investigation. The effect of resumption of a muscle-stretching program is of interest due to the a p parent lack of consistency in maintaining stretching programs by athletes and previously discharged clients. Therefore, the purpose of the present study was to investigate the effects of cessation and resumption of a static hamstring stretching protocol on joint ROM. It was hypothesized that ROM would increase after 6 weeks of stretching, but this increase would not be maintained after the 4 weeks of cessation of stretching, and the resumption of stretching would return the ROM to the magnitude similar to or greater than that attained after the initial 6 weeks of stretching. METHODS Subjects Twenty-four college-aged men and women with no history of pathology of the knee, hip, low back, or neurological problems volunteered for participation in this study. After the study was initiated, 6 subjects were excused from the study due to initiation of a fitness program or injury unrelated to participation in this study. Eighteen subjects completed the study (12 men, 6 women, mean age 21.0 years). The subjects were recruited from a sampling of convenience (ie, college students). All subjects signed a consent form approved by the Ohio University Institutional Review Board prior to participation in the study. Subjects were included in the study if they had short hamstrings operationally defined as a knee angle of less than 160" of knee extension with the hip held in 90" of flexion (Figure 1). This inclusion criteria was applied to both lower limbs. The subjects were not allowed to perform any lower extremity exercises with the exception of activities of daily living and occasional recreational activity, which was limited to no more than twice a week. In addition, subjects were excluded if they had been involved in a specific lower extremity flexibility program within the past 2 years. Study Design This study lasted for a total of 16 weeks. The first 6 weeks consisted of the initial stretching period. The next 4 weeks represented the cessation of I Orthoo Swrts Phvs Ther*Volume 31.Number 3-March 2001

FIGURE 1. The knee extension range of motion test of hamstring extensibility. stretching period followed by an additional &week stretching period (resumption of stretching). Testing was conducted prior to (Pretest 1) and at the end of the initial stretching period (Posttest 1). at the conclusion of the cessation period (Pretest 2), and at the end of the resumption period (Posttest 2) for a total of 4 evaluation sessions. For each subject, 1 leg was randomly selected for stretching while the other leg served as a control. This design was chosen so that each leg would have the same activity level (with the exception of stretching) and because there is no known effect of stretching 1 leg on the ROM of the other leg. Range of motion measurements were compared between limbs at Pretest 1 and Pretest 2. Within each limb, the ROM was compared between Pretest 1 and Pretest 2 to determine if there were any differences in ROM at the beginning of each &week stretching session. Range of motion testing was done at each of the 4 testing sessions on both legs. Procedure and Equipment The subjects performed a 5minute warm-up session on a stationary bicycle at a moderate intensity where they could easily hold a conversation without hyperventilating. Immediately after the warm-up session was completed, the subjects were placed in a supine position on a plinth, and the pelvis was stabilized with a strap at the level of the anterior superior iliac spine. At this time, the lateral femoral condyle and the lateral malleolus were marked for ROM measurements. Hamstring ROM was assessed by an adaptation of the supine active knee extension test as described by Gajdosik and Lusin4 (Figure 1). The subject's hip was placed in 90" of hip flexion. The subject was asked to actively extend the knee 5 times for an additional warm-up. Following the warm-up, the patient's hip was placed at 90" of hip flexion using a goniometer while an assistant held the thigh without excessively compressing the posterior thigh. The subject was then asked to actively extend the knee to the point of significant stretching pain at which time the knee angle measurement was taken. It is important to extend the knee to the point of significant stretching pain in order to accommodate the increase in "stretch tolerance" with a consistent end point on successive meas~rements.~j~ The testing procedure was repeated for the same leg and the highest knee ROM measurement was recorded. The procedure was then repeated for the contralateral leg. Although there were 3 examiners taking ROM measurements, the examiner remained constant for each respective subject for the duration of the study. In pilot experiments, subjects, other than those involved in the training study, were measured twice by each tester to determine intrarater and interrater reliability of the knee ROM measurement (n = 13, mean age 23.9 + 3.4 years). Intraclass correlation co- J Orthop Sports Phys Ther-Volume 31.Number 3-March 2001

FIGURE 2. Stretching procedure. efficients (ICC) were calculated for the knee ROM measurement and found to be 0.91 (tester l), 0.92 (tester 2), 0.82 (tester 3) for intrarater reliability (ICC,,), and 0.87 for interrater reliability (ICC,,).17 Stretching Protocol All participants were instructed on how to achieve and maintain an anterior pelvic tilt position while standing. It was determined that this position would help the subject achieve maximal stretch of the hamstring~.~~ The leg to be stretched was determined randomly (10 right legs, 8 left legs). To stretch the hamstring musculature, each subject was instructed to stand erect on the control leg with the foot pointing straight ahead. The subjects stretched the other leg by placing the heel on an elevated surface (eg, a chair) approximately knee to waist high, with the knee fully extended, head forward, and the hip in 0" of rotation. Arms were held parallel to the floor to discourage spinal flexion (Figure 2). After achieving the described position, the subject flexed forward at the hip until they perceived significant hamstring discomfort (a stretch sensation). Each subject was instructed to maintain the stretch sensation produced during the 30-second stretch and on any subsequent stretches during the study. This ensured that the sub jects would take up any slack produced during the J Orthop Sports Phys Ther*Volume 31.Number SoMarch 2001 141

TABLE. Two-factor repeated measures ANOVA summary of the effects based on Figure 3 data. Source df MS F Time 3 415.2 21.1. Error (time) 51 19.7 Limb 1 324.0 10.2' Error (limb) 17 31.8 Time x limb 3 156.9 Error (time x limb) 51 7.8 20.1' Journal of Orthopaedic & Sports Physical Therapy duration of the stretch due to possible viscoelastic relaxation of the hamstring musculotendinous unit and due to increases in ROM. Once subjects demonstrated competency in achieving and maintaining the stretch position, they were instructed to perform the stretch for a 30-second interval. This stretching period was followed by a 30- second rest period immediately followed by a second 30-second stretching repetition. Therefore, a total of 2 30-second stretching repetitions were interrupted by a 30-second rest period per stretching session. The subject performed the stretching protocol once per day, 5 times a week. Subjects kept a log stating the specific day and time which they performed the stretches. Subjects were reassessed at 3 weeks into each &week stretching period to assure maintenance of proper stretching techniques. Statistical Analysis A 2-factor (time and limb) repeated measures ANOVA was utilized for this study (SPSS Version 8.0) due to the multiple measures over time. The data were analyzed to determine primarily the significant changes over time and secondarily to compare between stretch and control legs over time. If main effects were found to be statistically significant, Tukey's Honestly Significant Difference post hoc analysis was used to identify which measures were significant. Significant differences were accepted at an alpha level of 0.05. RESULTS The 2-factor repeated measures ANOVA showed that there was a significant effect of time, limb, and the interaction between time and limb (see Table). Therefore, each limb (stretch limb and control limb) was analyzed with a separate repeated measures ANOVA to analyze the effect of time for each limb. Knee ROM in the stretched leg changed significantly over time (Figure 3, df = 3, F = 33.7, P < 0.05). Post hoc analysis revealed that a significant increase (P < 0.05) occurred between Pretest 1 and Posttest 1 (stretching period), and between Pretest 2 and Posttest 2 (resumption of stretching). Knee ROM decreased significantly (P < 0.05) from Posttest 1 to Stretch Control FIGURE 3. Stretch leg knee ROM increased significantly (P < 0.05) from 143.0 5 11.lo to 152.3 2 9.4" following the initial stretching period (Post- test 1). Knee ROM decreased significantly (P < 0.05) after the cessation period (Pretest 2) to 145.2 t 8.4" but was not significantly different from the initial measurement (Pretest 1). Following the final stretching period (Posttest 2), knee ROM increased significantly (P < 0.05) to 154.3 t 9.6", which was not significantly different than the ROM following the initial stretching period (Posttest 1). Knee ROM of 90" was the starting point of the test and 180" represents full extension. Pretest 2 (cessation period). Post hoc analysis also revealed no significant difference between Pretest 1 and Pretest 2 or between Posttest 1 and Posttest 2 in the stretch limb. Knee ROM in the control limb did not change significantly over time (df = 3, F = 3.0, P > 0.05). The comparison between stretch and control limbs was of interest primarily to determine if there were differences between the limbs at the 2 pretest times. As mentioned above, the 2-factor repeated measures ANOVA showed a significant effect of limb. However, post hoc analysis showed that there was no difference in knee ROM between the stretch and control legs at either the Pretest 1 or the Pretest 2 measurements. This, combined with the lack of difference between Pretest 1 and Pretest 2 within the control limb, confirms the assumption that the stretching exercises or other daily activities did not have a differential effect on control leg ROM. The stretch limb ROM was significantly greater than the control limb ROM at Posttest 1 and Posttest 2 (P < 0.05). DISCUSSION As expected, the &week hamstring static-stretching regimen resulted in a significant gain in knee ROM, which is consistent with current literat~re.~-~j* More importantly, this study showed there was no retention of the increased ROM. In fact, the ROM returned to baseline following the 4week cessation period so that the Pretest 1 and the Pretest 2 measurements were not statistically different. Resumption of the stretching regimen resulted in a significant gain in ROM, which was similar in magnitude to the gain in ROM J Orthop Sports Phys Ther.Volume 31 -Number 3.March 2001

during the initial stretching period. These results differ from Zebas and colleag~es~~ who demonstrated that following a &week static or PNF stretching regimen, significant ROM retention resulted at 2 weeks and again at 4 weeks postcessation. The comparison between the 2 studies is difficult, however, because their description of the stretching protocol and ROM measurements are unclear. For instance, Zebas et a126 described significant ROM changes at the ankle, hip, trunk, shoulders, and neck without defining the duration of stretches or which muscles were evaluated. To our knowledge, no other studies have evaluated the effects of resumption of a static stretching program. The results of this study indicated that the second &week stretching period did not result in greater gains in knee joint ROM compared to the first stretching period. If the first stretching period had some effect on the ROM gains in the second stretching period (a rebound effect), one might expect additional gains in ROM after the resumption period. On the other hand, it may be more likely that a rebound effect would have caused a more rapid return of knee joint ROM than the rate of gain of ROM in the initial stretching period. For instance, a very rap id return to ROM gains may have resulted after only 1 week, but the design of this study did not allow for the investigation of a possible rapid rebound effect. Stretching exercises are widely used in rehabilitation of the recreational or professional athlete. The specific goal of stretching exercises is to increase ROM, thus, increase functional capabilities and prevent injuries. Therapeutically, stretching exercises have been prescribed for patients with adaptive shortening of muscle, tendon, or joint structures due to postural problems, biomechanical problems, immobilization, improper positioning, or long term disability. Patients are likely to perform the stretching exercises during the time that they are being monitored by the therapist; however, after being discharged or when the symptoms subside, the majority of patients do not comply with part or all of the home exercise program.lg Based on the results presented here, the benefits of the stretching exercise will be lost relatively quickly if stretching is not continued. Performing the stretching exercises as little as 1 time per week will be sufficient to maintain the increased ROM.25 Recreational athletes are typically inconsistent in their exercise programs. The stopping and starting of the stretching program appears to add no particular benefit to the athlete. In comparison to muscle stretching, muscle strengthening results in well documented structural and physiological changes that may be related to the retention of strength after long periods of cessation of strengthening exercise^.^" However, the same cannot be said about muscle stretching exercises as they are used ~linically.~j~ This suggests that increased ROM after stretching may not be due to changes in the structure of the muscle and connective tissue, but possibly an increase in the tolerance to stret~h.~.'~ If structural changes do in fact occur with short periods of muscle stretching, they are short lived. CONCLUSION It is evident that this &week static-stretching regimen increased knee joint ROM. There did not a p pear to be a significant retention of the ROM benefits after a 4week cessation period and resumption of a musclestretching program did not appear to enhance the ROM gains that resulted from the initial stretching period. 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