International Journal of Sports Physiology and Performance, 2015, 10, 117-119 http://dx.doi.org/10.1123/ijspp.2013-0555 © 2015 Human Kinetics, Inc.
www.IJSPP-Journal.com BRIEF REPORT
Direct Relation of Acute Effects of Static Stretching on Isokinetic Torque Production With Initial Flexibility Level Nicolas Babault, Wacef Bazine, Gaëlle Deley, Christos Paizis, and Grégory Lattier Purpose: To examine the acute effect of a single static-stretching session of hamstring muscles on torque production in relation with individual flexibility. Methods: Maximal voluntary concentric torque of hamstring muscles was measured before and after a static-stretching session (6 × 30 s). Torque changes were correlated with the flexibility level determined at the onset of the experimental procedure. Results: The hamstring-stretching intervention significantly reduced maximal concentric torque in participants with low and high hamstring flexibility. Hamstring flexibility and torque decrease, determined immediately after the stretching procedure, were negatively correlated. Conclusions: Torque decrease measured after the static-stretching session is dependent on participant flexibility. Participants with low flexibility are much more likely to demonstrate large torque decreases poststretching. Keywords: hamstring, strength, correlation, recovery Static stretching is well known to increase range of motion around a joint, but numerous studies also demonstrated detrimental acute effects of stretching on subsequent muscle performance, such as muscle strength1 and vertical jump.2 The magnitude of these decreases could be attributed to stretch duration or intensity but also to the studied population. For instance, it has been suggested that trained athletes were less susceptible to the stretching-induced deficits than untrained athletes.3 Surprisingly, while comparing individuals with various flexibility levels, Behm et al4 did not demonstrate that the initial flexibility could affect stretch-induced deficits. However, in that study, short-duration static stretches were used.4 Indeed, it is well established that stretching-induced deficits are dependent on stretch duration; the longer the stretch durations, the greater the force reductions.5,6 While static stretching shorter than 30 seconds produces trivial force decreases, solid evidence of force decreases are present in the literature with longer duration (>90 s).5 Thus, it could be questioned whether the stretchinginduced strength deficit could be influenced by the initial flexibility with longer stretch durations. Therefore, the current study aimed to investigate the acute effects of six 30-second static stretches on hamstring strength in participants with various flexibility.
Methods Participants Eighteen men participated in this observational study (age 23 ± 2 y, height 174 ± 5 cm, body mass 75 ± 5 kg). All were recreationally active with ~5 hours training per week. All were healthy and free of lower-limb injury in the 6 months preceding the study, and none presented hamstring dysfunctionality. Participants were classified according to their active hamstring flexibility (ie, range of motion). The authors are with the Faculty of Sport Sciences, University of Bourgogne, Dijon, France. Address author correspondence to Nicolas Babault at [email protected].
They were ranked into LOW or HIGH when flexibility was lower or higher than the median value, respectively. Both LOW and HIGH groups included 9 participants. They agreed to participate in the study and signed an informed-consent form. The study was conducted according to the Declaration of Helsinki and approved by the local committee on human research.
Methodology Participants first performed a 5-minute standardized warm-up. Briefly, it consisted of submaximal jogging and various dynamic runs (eg, high knees, butt kicks). Then, they were positioned on a Biodex isokinetic ergometer (Biodex Corp, Shirley, NY) for righthamstring testing. Participants laid supine with both thighs vertical (hip flexion = 90°). The left leg was placed relaxed on a box with a 90° knee-joint angle. The right knee-joint axis was aligned with the dynamometer rotation axis, and the right leg was attached to the dynamometer lever arm. The pelvis and upper trunk were stabilized with Velcro straps. Arms were positioned across the chest with each hand clasping the opposite shoulder. Familiarization repetitions (6–10 submaximal concentric contractions) were then performed on the ergometer. About 3 minutes after warm-up and familiarization, active hamstring flexibility was measured through an active knee extension of the quadriceps muscles. Starting from a 90° knee-flexion angle, participants were asked to voluntarily extend the knee joint until maximal extension. The corresponding knee-joint range of motion was measured by the ergometer and used for participants’ hamstring-flexibility ranking. Then an assisted static-stretching procedure consisting of 6 × 30-second knee extension maintained at the point of discomfort was performed. Fifteen seconds of rest at a 90° knee-flexion angle were allowed between stretches. Maximal voluntary hamstring contractions were conducted before and immediately, 3 minutes, and 6 minutes after this stretching procedure. Torque was measured in concentric conditions using a 30°/s angular velocity and 80° range of motion (from 20° to 100° knee flexion). Two consecutive trials were performed, and the highest
117
118 Babault et al
torque value was retained for analyses. Participants were verbally encouraged to produce the maximal voluntary contraction possible.
Statistical Analysis A 2-way analysis of variance with repeated measures (group × time) was performed. Group (participants ranked LOW or HIGH) was used as the independent variable. Time was used as the dependent variable and referred to the different hamstring torque measurements. Tukey honestly-significant-difference post hoc analyses were subsequently used. Statistical significance was accepted at an alpha level of .05. Pearson product correlation was used to determine the relationship between flexibility and hamstring torque alteration.
Downloaded by ETSU on 09/18/16, Volume 10, Article Number 1
Results Hamstring range of motion was significantly different between groups (P < .05), with 51° ± 4° and 82° ± 6° for LOW and HIGH groups, respectively. Immediately after the stretching procedure, hamstring torque significantly decreased in both groups (from 127.9 ± 8.2 N·m to 110.1 ± 10.4 N·m, P = .0001, and from 123.2 ± 9.6 N·m to 118.5 ± 6.5 N·m, P = .02, for LOW and HIGH participants, respectively). Significantly greater torque decreases (P = .0001) were obtained for LOW participants than HIGH (Figure 1). Six minutes after stretching, although a significant restoration was observed, hamstring torque was still lower than baseline for LOW participants, while it returned to baseline for HIGH participants. Correlation between flexibility and hamstring-torque decrease determined immediately after the stretching procedure revealed a significant negative relationship (Figure 2).
Discussion The current study aimed to investigate the acute effects of stretching on torque production in relation with the amount of flexibility. After 6 × 30 seconds of hamstring stretching, we observed a significant
Figure 1 — Hamstring torque decrease measured immediately (POST), 3 minutes (POST3), and 6 minutes (POST6) after the stretching procedure. Values are mean percentages expressed with respect to baseline ± SD. $Significant difference from LOW for the same period (P < .05). £Significant difference from POST for the same group (P < .05).
Figure 2 — Relationship between hamstring flexibility and torque changes immediately after the stretching procedure.
torque decrease 4 times larger in participants with low flexibility than in more flexible ones. Stretching-induced torque decreases therefore appear to be dependent on individual flexibility. Previous studies investigated stretching-induced force decreases in different populations. Most of them considered gender,7 age,8 trained versus untrained participants,3 or the effects of stretchtraining programs.9 From these studies, some indirect evidences seem to confirm our findings. Indeed, recent experiments have demonstrated that stretching during warm-up is not detrimental to performance in dancers,10 a population with high flexibility. These results are partly confirmed in another study conducted on modern dancers in fast but not slow isokinetic conditions.11 In contrast, static stretching may negatively affect leaping performance in elite rhythmic gymnasts.12 Although the previously cited factors (eg, gender, age, sport, training) may affect muscle–tendon stiffness or muscle viscoelastic properties, and therefore flexibility, conflicting results are often reported, making comparisons difficult.5 Similarly to our study, 1 experiment directly compared individuals with different levels of flexibility4 but found results opposite to ours. Indeed, with our stretching procedure, torque decreases were dependent on the amount of flexibility, while Behm et al4 did not find any correlation with a shorter stretching procedure. The hypothesis addressed by those authors was that, irrespective of the individual’s flexibility, stretching until the point of discomfort produces similar relative stress of the musculotendinous unit and therefore similar strength and power impairments. These apparently conflicting findings might partly originate from the different stretch durations used (6 × 30 s here vs 3 × 30 s for Behm et al4). Indeed, it is well established that stretching-induced deficits are dependent on stretch durations, greater force reductions and lower intersubject variation being generally observed with longer stretch durations.5,6 According to the sigmoidal shape of this dose response, it could be hypothesized that long stretch durations would exacerbate the stretching-induced effects in individuals with low flexibility, while it would plateau and remain low in more-flexible participants. Additional experiments are required to test this hypothesis.
Acute Stretching and Flexibility 119
Conclusions and Practical Applications
Downloaded by ETSU on 09/18/16, Volume 10, Article Number 1
In conclusion, the acute effects of static stretching on torque production are dependent on the individual’s flexibility; the greater the flexibility, the lower and shorter the torque decreases. In addition, stretch-induced torque reduction recovered faster in individuals with high flexibility. This finding is not surprising since lower torque reductions are obtained with these participants. Nevertheless, this study was conducted on a small sample and using 1 specific joint configuration. It could be of interest to replicate this study with a larger sample including various sports, male athletes, female athletes, and different muscle groups. Taken all together, these results may have large practical applications. Indeed, most studies dissuade athletes from performing static stretching during warm-up. From the current results, it is now suggested that static stretching during warm-up in individuals with high flexibility (often associated with sports with important specific flexibility applications) could be performed with smaller and shorter detrimental effects than in individuals with low flexibility.
References 1. Gergley JC. Acute effect of passive static stretching on lowerbody strength in moderately trained men. J Strength Cond Res. 2013;27(4):973–977. PubMed doi:10.1519/JSC.0b013e318260b7ce 2. Fortier J, Lattier G, Babault N. Acute effects of short-duration isolated static stretching or combined with dynamic exercises on strength, jump and sprint performance. Sci Sports. 2013;28:e111–e117. doi:10.1016/j. scispo.2012.11.003 3. Egan AD, Cramer JT, Massey LL, Marek SM. Acute effects of static stretching on peak torque and mean power output in National Col-
legiate Athletic Association Division I women’s basketball players. J Strength Cond Res. 2006;20(4):778–782. PubMed 4. Behm DG, Bradbury EE, Haynes AT, Hodder JN, Leonard AM, Paddock NR. Flexibility is not related to stretch-induced deficits in force or power. J Sports Sci Med. 2006;5:33–42. PubMed 5. Behm DG, Chaouachi A. A review of the acute effects of static and dynamic stretching on performance. Eur J Appl Physiol. 2011;111(11):2633–2651. PubMed doi:10.1007/s00421-011-1879-2 6. Kay AD, Blazevich AJ. Effect of acute static stretch on maximal muscle performance: a systematic review. Med Sci Sports Exerc. 2012;44(1):154–164. PubMed doi:10.1249/MSS.0b013e318225cb27 7. Costa PB, Ryan ED, Herda TJ, Walter AA, Hoge KM, Cramer JT. Acute effects of passive stretching on the electromechanical delay and evoked twitch properties: a gender comparison. J Appl Biomech. 2012;28(6):645–654. PubMed 8. Handrakis JP, Southard VN, Abreu JM, et al. Static stretching does not impair performance in active middle-aged adults. J Strength Cond Res. 2010;24(3):825–830. PubMed doi:10.1519/JSC.0b013e3181ad4f89 9. Chaouachi A, Chamari K, Wong P, et al. Stretch and sprint training reduces stretch-induced sprint performance deficits in 13- to 15-yearold youth. Eur J Appl Physiol. 2008;104(3):515–522. PubMed doi:10.1007/s00421-008-0799-2 10. Morrin N, Redding E. Acute effects of warm-up stretch protocols on balance, vertical jump height, and range of motion in dancers. J Dance Med Sci. 2013;17(1):34–40. PubMed doi:10.12678/1089-313X.17.1.34 11. Agopyan A, Tekin D, Unal M, Kurtel H, Turan G, Ersoz A. Acute effects of static stretching on isokinetic thigh strength on modern dancers. J Sports Med Phys Fitness. 2013;53(5):538–550. PubMed 12. Di Cagno A, Baldari C, Battaglia C, et al. Preexercise static stretching effect on leaping performance in elite rhythmic gymnasts. J Strength Cond Res. 2010;24(8):1995–2000. PubMed doi:10.1519/ JSC.0b013e3181e34811
www.IJSPP-Journal.com BRIEF REPORT
Direct Relation of Acute Effects of Static Stretching on Isokinetic Torque Production With Initial Flexibility Level Nicolas Babault, Wacef Bazine, Gaëlle Deley, Christos Paizis, and Grégory Lattier Purpose: To examine the acute effect of a single static-stretching session of hamstring muscles on torque production in relation with individual flexibility. Methods: Maximal voluntary concentric torque of hamstring muscles was measured before and after a static-stretching session (6 × 30 s). Torque changes were correlated with the flexibility level determined at the onset of the experimental procedure. Results: The hamstring-stretching intervention significantly reduced maximal concentric torque in participants with low and high hamstring flexibility. Hamstring flexibility and torque decrease, determined immediately after the stretching procedure, were negatively correlated. Conclusions: Torque decrease measured after the static-stretching session is dependent on participant flexibility. Participants with low flexibility are much more likely to demonstrate large torque decreases poststretching. Keywords: hamstring, strength, correlation, recovery Static stretching is well known to increase range of motion around a joint, but numerous studies also demonstrated detrimental acute effects of stretching on subsequent muscle performance, such as muscle strength1 and vertical jump.2 The magnitude of these decreases could be attributed to stretch duration or intensity but also to the studied population. For instance, it has been suggested that trained athletes were less susceptible to the stretching-induced deficits than untrained athletes.3 Surprisingly, while comparing individuals with various flexibility levels, Behm et al4 did not demonstrate that the initial flexibility could affect stretch-induced deficits. However, in that study, short-duration static stretches were used.4 Indeed, it is well established that stretching-induced deficits are dependent on stretch duration; the longer the stretch durations, the greater the force reductions.5,6 While static stretching shorter than 30 seconds produces trivial force decreases, solid evidence of force decreases are present in the literature with longer duration (>90 s).5 Thus, it could be questioned whether the stretchinginduced strength deficit could be influenced by the initial flexibility with longer stretch durations. Therefore, the current study aimed to investigate the acute effects of six 30-second static stretches on hamstring strength in participants with various flexibility.
Methods Participants Eighteen men participated in this observational study (age 23 ± 2 y, height 174 ± 5 cm, body mass 75 ± 5 kg). All were recreationally active with ~5 hours training per week. All were healthy and free of lower-limb injury in the 6 months preceding the study, and none presented hamstring dysfunctionality. Participants were classified according to their active hamstring flexibility (ie, range of motion). The authors are with the Faculty of Sport Sciences, University of Bourgogne, Dijon, France. Address author correspondence to Nicolas Babault at [email protected].
They were ranked into LOW or HIGH when flexibility was lower or higher than the median value, respectively. Both LOW and HIGH groups included 9 participants. They agreed to participate in the study and signed an informed-consent form. The study was conducted according to the Declaration of Helsinki and approved by the local committee on human research.
Methodology Participants first performed a 5-minute standardized warm-up. Briefly, it consisted of submaximal jogging and various dynamic runs (eg, high knees, butt kicks). Then, they were positioned on a Biodex isokinetic ergometer (Biodex Corp, Shirley, NY) for righthamstring testing. Participants laid supine with both thighs vertical (hip flexion = 90°). The left leg was placed relaxed on a box with a 90° knee-joint angle. The right knee-joint axis was aligned with the dynamometer rotation axis, and the right leg was attached to the dynamometer lever arm. The pelvis and upper trunk were stabilized with Velcro straps. Arms were positioned across the chest with each hand clasping the opposite shoulder. Familiarization repetitions (6–10 submaximal concentric contractions) were then performed on the ergometer. About 3 minutes after warm-up and familiarization, active hamstring flexibility was measured through an active knee extension of the quadriceps muscles. Starting from a 90° knee-flexion angle, participants were asked to voluntarily extend the knee joint until maximal extension. The corresponding knee-joint range of motion was measured by the ergometer and used for participants’ hamstring-flexibility ranking. Then an assisted static-stretching procedure consisting of 6 × 30-second knee extension maintained at the point of discomfort was performed. Fifteen seconds of rest at a 90° knee-flexion angle were allowed between stretches. Maximal voluntary hamstring contractions were conducted before and immediately, 3 minutes, and 6 minutes after this stretching procedure. Torque was measured in concentric conditions using a 30°/s angular velocity and 80° range of motion (from 20° to 100° knee flexion). Two consecutive trials were performed, and the highest
117
118 Babault et al
torque value was retained for analyses. Participants were verbally encouraged to produce the maximal voluntary contraction possible.
Statistical Analysis A 2-way analysis of variance with repeated measures (group × time) was performed. Group (participants ranked LOW or HIGH) was used as the independent variable. Time was used as the dependent variable and referred to the different hamstring torque measurements. Tukey honestly-significant-difference post hoc analyses were subsequently used. Statistical significance was accepted at an alpha level of .05. Pearson product correlation was used to determine the relationship between flexibility and hamstring torque alteration.
Downloaded by ETSU on 09/18/16, Volume 10, Article Number 1
Results Hamstring range of motion was significantly different between groups (P < .05), with 51° ± 4° and 82° ± 6° for LOW and HIGH groups, respectively. Immediately after the stretching procedure, hamstring torque significantly decreased in both groups (from 127.9 ± 8.2 N·m to 110.1 ± 10.4 N·m, P = .0001, and from 123.2 ± 9.6 N·m to 118.5 ± 6.5 N·m, P = .02, for LOW and HIGH participants, respectively). Significantly greater torque decreases (P = .0001) were obtained for LOW participants than HIGH (Figure 1). Six minutes after stretching, although a significant restoration was observed, hamstring torque was still lower than baseline for LOW participants, while it returned to baseline for HIGH participants. Correlation between flexibility and hamstring-torque decrease determined immediately after the stretching procedure revealed a significant negative relationship (Figure 2).
Discussion The current study aimed to investigate the acute effects of stretching on torque production in relation with the amount of flexibility. After 6 × 30 seconds of hamstring stretching, we observed a significant
Figure 1 — Hamstring torque decrease measured immediately (POST), 3 minutes (POST3), and 6 minutes (POST6) after the stretching procedure. Values are mean percentages expressed with respect to baseline ± SD. $Significant difference from LOW for the same period (P < .05). £Significant difference from POST for the same group (P < .05).
Figure 2 — Relationship between hamstring flexibility and torque changes immediately after the stretching procedure.
torque decrease 4 times larger in participants with low flexibility than in more flexible ones. Stretching-induced torque decreases therefore appear to be dependent on individual flexibility. Previous studies investigated stretching-induced force decreases in different populations. Most of them considered gender,7 age,8 trained versus untrained participants,3 or the effects of stretchtraining programs.9 From these studies, some indirect evidences seem to confirm our findings. Indeed, recent experiments have demonstrated that stretching during warm-up is not detrimental to performance in dancers,10 a population with high flexibility. These results are partly confirmed in another study conducted on modern dancers in fast but not slow isokinetic conditions.11 In contrast, static stretching may negatively affect leaping performance in elite rhythmic gymnasts.12 Although the previously cited factors (eg, gender, age, sport, training) may affect muscle–tendon stiffness or muscle viscoelastic properties, and therefore flexibility, conflicting results are often reported, making comparisons difficult.5 Similarly to our study, 1 experiment directly compared individuals with different levels of flexibility4 but found results opposite to ours. Indeed, with our stretching procedure, torque decreases were dependent on the amount of flexibility, while Behm et al4 did not find any correlation with a shorter stretching procedure. The hypothesis addressed by those authors was that, irrespective of the individual’s flexibility, stretching until the point of discomfort produces similar relative stress of the musculotendinous unit and therefore similar strength and power impairments. These apparently conflicting findings might partly originate from the different stretch durations used (6 × 30 s here vs 3 × 30 s for Behm et al4). Indeed, it is well established that stretching-induced deficits are dependent on stretch durations, greater force reductions and lower intersubject variation being generally observed with longer stretch durations.5,6 According to the sigmoidal shape of this dose response, it could be hypothesized that long stretch durations would exacerbate the stretching-induced effects in individuals with low flexibility, while it would plateau and remain low in more-flexible participants. Additional experiments are required to test this hypothesis.
Acute Stretching and Flexibility 119
Conclusions and Practical Applications
Downloaded by ETSU on 09/18/16, Volume 10, Article Number 1
In conclusion, the acute effects of static stretching on torque production are dependent on the individual’s flexibility; the greater the flexibility, the lower and shorter the torque decreases. In addition, stretch-induced torque reduction recovered faster in individuals with high flexibility. This finding is not surprising since lower torque reductions are obtained with these participants. Nevertheless, this study was conducted on a small sample and using 1 specific joint configuration. It could be of interest to replicate this study with a larger sample including various sports, male athletes, female athletes, and different muscle groups. Taken all together, these results may have large practical applications. Indeed, most studies dissuade athletes from performing static stretching during warm-up. From the current results, it is now suggested that static stretching during warm-up in individuals with high flexibility (often associated with sports with important specific flexibility applications) could be performed with smaller and shorter detrimental effects than in individuals with low flexibility.
References 1. Gergley JC. Acute effect of passive static stretching on lowerbody strength in moderately trained men. J Strength Cond Res. 2013;27(4):973–977. PubMed doi:10.1519/JSC.0b013e318260b7ce 2. Fortier J, Lattier G, Babault N. Acute effects of short-duration isolated static stretching or combined with dynamic exercises on strength, jump and sprint performance. Sci Sports. 2013;28:e111–e117. doi:10.1016/j. scispo.2012.11.003 3. Egan AD, Cramer JT, Massey LL, Marek SM. Acute effects of static stretching on peak torque and mean power output in National Col-
legiate Athletic Association Division I women’s basketball players. J Strength Cond Res. 2006;20(4):778–782. PubMed 4. Behm DG, Bradbury EE, Haynes AT, Hodder JN, Leonard AM, Paddock NR. Flexibility is not related to stretch-induced deficits in force or power. J Sports Sci Med. 2006;5:33–42. PubMed 5. Behm DG, Chaouachi A. A review of the acute effects of static and dynamic stretching on performance. Eur J Appl Physiol. 2011;111(11):2633–2651. PubMed doi:10.1007/s00421-011-1879-2 6. Kay AD, Blazevich AJ. Effect of acute static stretch on maximal muscle performance: a systematic review. Med Sci Sports Exerc. 2012;44(1):154–164. PubMed doi:10.1249/MSS.0b013e318225cb27 7. Costa PB, Ryan ED, Herda TJ, Walter AA, Hoge KM, Cramer JT. Acute effects of passive stretching on the electromechanical delay and evoked twitch properties: a gender comparison. J Appl Biomech. 2012;28(6):645–654. PubMed 8. Handrakis JP, Southard VN, Abreu JM, et al. Static stretching does not impair performance in active middle-aged adults. J Strength Cond Res. 2010;24(3):825–830. PubMed doi:10.1519/JSC.0b013e3181ad4f89 9. Chaouachi A, Chamari K, Wong P, et al. Stretch and sprint training reduces stretch-induced sprint performance deficits in 13- to 15-yearold youth. Eur J Appl Physiol. 2008;104(3):515–522. PubMed doi:10.1007/s00421-008-0799-2 10. Morrin N, Redding E. Acute effects of warm-up stretch protocols on balance, vertical jump height, and range of motion in dancers. J Dance Med Sci. 2013;17(1):34–40. PubMed doi:10.12678/1089-313X.17.1.34 11. Agopyan A, Tekin D, Unal M, Kurtel H, Turan G, Ersoz A. Acute effects of static stretching on isokinetic thigh strength on modern dancers. J Sports Med Phys Fitness. 2013;53(5):538–550. PubMed 12. Di Cagno A, Baldari C, Battaglia C, et al. Preexercise static stretching effect on leaping performance in elite rhythmic gymnasts. J Strength Cond Res. 2010;24(8):1995–2000. PubMed doi:10.1519/ JSC.0b013e3181e34811
