Post hoc power calculations confirmed that the statistical power (1 − β) was generally high, being 1.00 for SPT and SLR at each of 20, 60, 180, and 300 seconds. For DPT, the power was 0.06, 0.90, 1.00, and 1.00 for 20, 60, 180, and 300 seconds, respectively. For stiffness, the power was 0.12, 0.77, 1.00, and 1.00, respectively. For muscle force, the power was 0.99, 0.99, 1.00, and 0.99, respectively.
Static Passive Torque
There was an interaction effect between the stretching durations and prestretching or poststretching SPT values (p < 0.01; Figure 3A). Static passive torque decreased significantly after stretching for all durations of stretching (p < 0.05). The SPT after 60-, 180-, and 300-second stretching was significantly lower than after 20-second stretching (p < 0.05). There were no differences between the prestretching SPT values for all durations of stretching. The pre-post ratio of SPT for 180-second stretching was significantly lower than for 20-second stretching (p < 0.05), and the pre-post ratio of SPT for 300-second stretching was significantly lower than for the other stretching durations (p < 0.05).
Dynamic Passive Torque
There was no interaction effect between the durations of stretching and prestretching or poststretching DPT values. Dynamic passive torque decreased significantly after 180- and 300-second stretching (p < 0.05; Figure 3B). The DPT after 60- and 300-second stretching was significantly lower than after 20-second stretching (p < 0.05). There were no differences between the prestretching DPT values for all durations of stretching. There were no differences between the pre-post ratios of DPT for all durations of stretching. Similar results were obtained when we repeated the analysis excluding the interactive term (duration of stretch, p < 0.05; pre/post, p < 0.05; data not shown).
There was no interaction effect between the durations of stretching and prestretching or poststretching stiffness values. Stiffness decreased significantly after 180- and 300-second stretching (p < 0.05; Figure 3C). Stiffness after 300-second stretching was significantly lower than after 20-second stretching (p < 0.05). There were no differences between the prestretching stiffness values for all durations of stretching. There were no differences between the pre-post ratios of stiffness for all durations of stretching. Similar results were obtained when we repeated the analysis excluding the interactive term (duration of stretch, p < 0.05; pre/post, p < 0.05; data not shown).
Straight Leg Raise
There was an interaction effect between the durations of stretching and prestretching or poststretching SLR values (p < 0.01; Figure 3D). Straight leg raise increased significantly after stretching for all stretching durations (p < 0.05). The SLR after 180-second stretching was significantly greater than after 20-second stretching (p < 0.05). The SLR after 300-second stretching was significantly greater than after 20- and 60-second stretching (p < 0.05). There were no differences between the prestretching SLR values for all durations of stretching. The pre-post ratio of SLR for 180-second stretching was significantly greater than for 20-second stretching (p < 0.05). The pre-post ratio of SLR of 300-second stretching was significantly greater than for the other durations (p < 0.05). Straight leg raise measured at baseline was not significantly correlated with the changes in other parameters.
Isometric Muscle Force
There was no interaction effect between the durations of stretching and prestretching or poststretching isometric muscle force values. Isometric muscle force decreased significantly after stretching for all durations of stretching (p < 0.05; Figure 3E). There were no differences between the prestretchings and poststretching isometric muscle force values for all durations of stretching. There were also no differences between the pre-post ratios of isometric muscle force for all durations of stretching. When we repeated the analysis excluding the interactive term, the duration of stretch was not statistically significant (p > 0.05) whereas the pre-post effect was significant (p < 0.05; data not shown).
Correlation Coefficients Between the Durations of Stretching and the Amount of Change (Percentage) in Each Parameter
There was a strong negative correlation between the durations of stretching and the amount of change (%) for SPT (ρ = −0.742, p < 0.01), a moderate positive correlation with SLR (ρ = 0.577, p < 0.01), and a fair negative correlation with DPT (ρ = −0.255, p < 0.05) and stiffness (ρ = −0.235, p < 0.05). However, there was no significant correlation between the durations of stretching and the amount of change (percentage) for isometric muscle force (ρ = −0.08, p > 0.05).
This study investigated the acute effects of different static stretching durations (20, 60, 180, and 300 seconds) on SPT, DPT, stiffness, SLR, and isometric muscle force.
Static passive torque declined significantly after stretching for all durations of stretching. This result was consistent with that of previous studies (21–23,25,26). Research demonstrated that H-wave amplitude, the excitatory index of the anterior horn cell, declined during triceps surae stretching (10,12). This suggested that SPT decline in response to static stretching may be because of a neurophysiological mechanism. In addition, the present study found a strong negative correlation between the durations of stretching and the amount of change (percentage) in SPT. Duong et al. (8) reported that SPT decreased by approximately 20% after 5 minutes of triceps surae stretching and by approximately 42% after 42 minutes of triceps surae stretching. Their results and the present results suggest that the longer the duration of stretching, the greater the decline in SPT after stretching. Future research should simultaneously assess SPT and the H-reflex for the triceps surae to determine the relationship between neurophysiological mechanisms and changes in SPT in response to static stretching.
Dynamic passive torque and stiffness decreased significantly after 180- and 300-second stretching. In addition, DPT after 60- and 300-second stretching were significantly lower than after 20-second stretching, whereas stiffness after 300-second stretching was significantly lower than after 20-second stretching. These results were similar to previous studies where DPT and stiffness did not change after 90-second stretching (21) and then decreased significantly when stretching exceeded 120 seconds or totaled 300 seconds (4,28,33). Although SPT decreased after all durations of stretching, DPT and stiffness did not significantly change after stretching for 20 and 60 seconds. In addition, there were fair negative correlations between the durations of stretching and the amount of change (percentage) for DPT and stiffness. Dynamic passive torque and stiffness, calculated from torque-angle curve, are thought to reflect the viscoelasticity of the muscle-tendon unit (23,24). Although the muscle-tendon unit viscoelasticity did not change after 20 and 60 seconds of stretching, the decline in DPT and stiffness after 180 and 300 seconds of stretching possibly represented a significant improvement in the viscoelasticity of the muscle-tendon unit. In contrast, Halbertsma et al. (13) reported that stiffness did not change after 600-second stretching. In recent years, ultrasonography has been used to calculate the elastic (stiffness) and viscous (hysteresis) indexes for tendons (17,28). Future research should use these ultrasonography derived indexes to examine the relationship between the durations of stretching and DPT or stiffness. It was previously reported that the increment of tendon stiffness in long muscles might contribute to increased torque output after isometric training (19). Therefore, studies should also examine the direct impact of static stretching on the contribution of tendon stiffness, independent of muscle stiffness, to power output and flexibility of the muscle-tendon unit.
These observed results for SPT and DPT indicate that less force is required to maintain a static joint position or provide dynamic movement, whereas the reduction in stiffness indicates greater muscle and joint flexibility. These factors are associated with the risk of muscle injury during stretching and physical activity. Therefore, reducing SPT, DPT, and stiffness may reduce the risk of muscle damage.
Straight leg raise increased significantly after all durations of stretching. This result was consistent with those of previous studies (3,13,21,22,30). In addition, this study found a moderate positive correlation between the durations of stretching and the amount of change (percentage) for SLR. We suggest that the factors responsible for the increase in SLR were changes in muscle-tendon unit extensibility and viscoelasticity, and pain threshold. These factors may have been responsible for the SPT results, but do not explain the results for DPT and stiffness. Several studies reported that mobility was increased but that DPT and stiffness did not change after stretching (12,21,24). These studies suggested that the result was because an increase in stretch tolerance. Stretch tolerance was assessed as the joint angle at which the subjects felt a pain or discomfort while undergoing passive stretching (12,24). In support of the role of stretch tolerance, Magnusson et al. (24) reported that the knee extension angle, at which subjects felt pain in the hamstring, was increased despite DPT not changing after static hamstring stretching. These authors proposed that the knee extension angle increased because of an increase in stretch tolerance and not an improvement in hamstring viscoelasticity. Although they did not discuss the mechanism for the increase in stretch tolerance in detail, it was proposed that one of the responsible factors was an elevation in pain threshold. Fukunaga et al. (9) reported that there was a tendency for muscle blood flow to increase after stretching. Mense and Stahnke (27) reported that the activity of C-fiber during muscle contraction without muscular ischemia was significantly less than with muscular ischemia. Therefore, a relationship between muscle blood flow and pain threshold was suggested. Based on this previous research it is possible that the pain threshold for muscle stretching was elevated in this study. This may have been related to an increase in muscle blood flow caused by the stretching. Therefore, the increase in SLR after 20- and 60-second stretching was because of the increase in hamstring extensibility that was regulated by neurophysiological properties and an increased elevation in the pain threshold that was related to an increase in blood flow. This proposed mechanism is further supported by the finding that DPT and stiffness did not change significantly after 20- and 60-second stretching. In addition, it is suggested that the increase in SLR after 180- and 300-second stretching was because of an improvement in the viscoelasticity of the muscle-tendon unit in addition to the 2 factors discussed above, because DPT and stiffness declined significantly after 180- and 300-second stretching. From this discussion, it can be seen that an increase in muscle blood flow may play an important role in the alteration in muscle function with static stretching. Future research should examine the relationship between blood flow and mobility in response to static stretching.
Isometric muscle force decreased significantly after all durations of stretching. This result was consistent with previous studies, showing that muscle function deteriorates somewhat after static stretching in training programs (2,3,34). This reduction in isometric muscle force after static stretching, particularly with longer stretch durations, may be detrimental to performance. A recent systematic review of 106 studies of acute static stretching (14) revealed a dose-dependent relationship between duration of acute static stretching and muscle performance. The authors of that study reported that the detrimental effects of acute static stretching were mainly limited to stretches lasting ≥60 seconds, as shorter stretch durations had no detrimental (<30 seconds; pooled estimate = −1.1%) or no significant (30–45 seconds; pooled estimate = −1.9%) effects on performance. The effects of static stretch on performance were independent of performance task, contraction mode, or muscle group.
It is possible that the factors responsible for the decrease in isometric muscle force were changes in muscle-tendon unit extensibility and viscoelasticity, and neurophysiological properties. Siatras et al. (34) reported that isometric muscle force did not change after 10- and 20-second stretching, but decreased significantly after 30- and 60-second stretching. In contrast, we found that isometric muscle force decreased after 20 seconds of stretching. In support of this finding, McHugh et al. (25) reported that isometric knee flexion force decreased when hamstrings were in a shortened position after stretching, but not when they were in a lengthened position after stretching. It was argued that the decrease in isometric muscle force was because of a stretching induced increase in muscle extensibility. It was further argued that the decrease in isometric muscle force was because of a stretching induced alteration in the muscle length-tension relationship. In this study, it is possible that isometric knee flexion force decreased after stretching because muscle force was assessed with the hamstrings in a shortened position. Another factor responsible for the decrease in isometric force may have been related to the stretching induced alteration in SLR. This study found that SLR increased significantly after all durations of stretching. This increase in the muscle extensibility may have changed the muscle length-tension relationship, thereby decreasing isometric muscle force production. Another factor responsible for the decrease in muscle force after stretching may have been a change in muscle-tendon unit viscoelasticity (34,39). However, the DPT and stiffness results after 20- and 60-second stretching were not associated with the decrease in isometric force. Finally, we suggest that the decrease in isometric muscle force after stretching may have been because of neurophysiological alterations (34,39). Previous studies have found that electromyography (EMG) amplitude during maximum voluntary contraction decreased after stretching (2,5). Future research examining the relationship between stretching and isometric force should include the use of EMG to examine the neurophysiological determinants of alterations in performance. Studies should also examine whether the reduction in isometric force has any significant consequences on the performance of physical activities, and hence evaluate whether this factor outweighs the benefits of longer durations of stretch on muscle/joint flexibility. Considering that different stretch procedures may have differing effects on specific activities (32,35,38), this reduction in isometric force at longer static stretch durations may mean it should be reserved for specific activities requiring flexibility rather than force generation. However, as described by Kay and Blazevich (14), the decrease in performance may be small or unnoticed at shorter stretch durations, and that maintaining a static stretch for ≥60 seconds is uncommon in preexercise routines, so the relative impact of this physiological phenomenon on performance is likely to be small.
This reduction in muscle force (performance) may be a trade-off for achieving greater joint flexibility/reduced muscle stiffness with longer durations of static stretches. Several studies have demonstrated that static stretching training programs achieve meaningful improvements in joint flexibility (6,32). Because there appeared to be no marked differences between dynamic and static stretching in the improvements in flexibility, the use of dynamic stretching may be preferred for training and warm-up programs in individuals requiring muscle power or a balance between muscle power and flexibility. Intriguingly, however, a short-term study examining the effects of warm-up stretching on hamstring flexibility in individuals with prior injury suggested that static stretching, but not dynamic stretching, increased hamstring flexibility (31). This effect was apparent, but not significant, in individuals with reduced flexibility postinjury. This raises the question of whether static stretching, as in this study, could be more beneficial in facilitating the recovery from injury, and whether longer durations of stretch may allow quicker recovery of muscle flexibility.
This study found that the longer the duration of stretching, the more SPT and SLR changed after stretching. In addition, to improve DPT and stiffness, it is suggested that longer durations of static stretching may be required. Thus, it is possible that static stretching should be performed longer than it is performed generally to improve flexibility and reduce the risk of muscle/joint injury. However, there may be a threshold level for optimum performance, as the longest duration of stretching tested in this study resulted in a decrease in isometric force. Further studies are necessary to investigate the effects of stretching intensity, duration, and frequency to not only resolve the current discrepancies among prior studies, but also help to guide the development of future recommendations for static stretching before physical activity. It is also possible that static stretching programs would facilitate the recovery from injury in terms of improving muscle flexibility. This is an interesting concept that would need to be carefully examined by comparing the effects of stretch duration and type of stretch on the restoration of flexibility. Additionally, future studies should examine the implications of the reduced isometric force observed in this study with longer durations of stretching, and whether this limitation outweighs the potential benefits of longer stretching on flexibility, for example.
This work was supported in part by a grant from A-kit Co., Ltd. and the Public Advertisement Research Project of Nihon Fukushi University. All the authors declare that there is no potential conflict of interest regarding this article. This study does not indicate endorsement by the National Strength and Conditioning Association.
1. American College of Sports Medicine. Guidelines for Exercise Testing and Prescription. Philadelphia, PA: Lippincott Williams & Wilkins, 2006.
2. Babault N, Kouassi BY, Desbrosses K. Acute effects of 15 min static or contract-relax stretching modalities on plantar flexors neuromuscular properties. J Sci Med Sport 13: 247–252, 2009.
3. Brandenburg JP. Duration of stretch does not influence the degree of force loss following static stretching
. J Sports Med Phys Fitness 46: 526–534, 2006.
4. Burgess KE, Graham-Smith P, Pearson SJ. Effect of acute tensile loading on gender-specific tendon structural and mechanical properties. J Orthop Res 27: 510–516, 2009.
5. Cramer JT, Housh TJ, Weir JP, Johnson GO, Coburn JW, Beck TW. The acute effects of static stretching
on peak torque, mean power output, electromyography, and mechanomyography. Eur J Appl Physiol 93: 530–539, 2005.
6. Dalrymple KJ, Davis SE, Dwyer GB, Moir GL. Effect of static and dynamic stretching on vertical jump performance in collegiate women volleyball players. J Strength Cond Res 24: 149–155, 2010.
7. Decoster LC, Cleland J, Altieri C, Russell P. The effects of hamstring stretching on range of motion: A systematic literature review. J Orthop Sports Phys Ther 35: 377–387, 2005.
8. Duong B, Low M, Moseley AM, Lee RY, Herbert RD. Time course of stress relaxation and recovery in human ankles. Clin Biomech (Bristol, Avon) 16: 601–607, 2001.
9. Fukunaga T, Yada H. Effect of static stretching
on forearm blood flow. Descente Sports Sci 4: 192–195, 1983.
10. Funase K, Higashi T, Sakakibara A, Tanaka K, Takemochi K, Ogahara K, Iwanaga R. Neural mechanism underlying the H-reflex inhibition during static muscle stretching. Adv Exer Sports Physiol 9: 119–127, 2003.
11. Gajdosik RL, Vander Linden DW, Williams AK. Influence of age on concentric isokinetic torque and passive extensibility variables of the calf muscles of women. Eur J Appl Physiol Occup Physiol 74: 279–286, 1996.
12. Guissard N, Duchateau J, Hainaut K. Muscle stretching and motoneuron excitability. Eur J Appl Physiol Occup Physiol 58: 47–52, 1988.
13. Halbertsma JP, van Bolhuis AI, Goeken LN. Sport stretching: Effect on passive muscle stiffness
of short hamstrings. Arch Phys Med Rehabil 77: 688–692, 1996.
14. Kay AD, Blazevich AJ. Effect of acute static stretch on maximal muscle performance: A systematic review. Med Sci Sports Exerc 44: 154–164, 2012.
15. Kokkonen J, Nelson AG, Cornwell A. Acute muscle stretching inhibits maximal strength performance. Res Q Exerc Sport 69: 411–415, 1998.
16. Kubo K, Kanehisa H, Fukunaga T. Effects of viscoelastic properties of tendon structures on stretch-shortening cycle exercise in vivo. J Sports Sci 23: 851–860, 2005.
17. Kubo K, Kanehisa H, Kawakami Y, Fukunaga T. Influence of static stretching
on viscoelastic properties of human tendon structures in vivo. J Appl Physiol 90: 520–527, 2001.
18. Kubo K, Morimoto M, Komuro T, Tsunoda N, Kanehisa H, Fukunaga T. Influences of tendon stiffness
, joint stiffness
, and electromyographic activity on jump performances using single joint. Eur J Appl Physiol 99: 235–243, 2007.
19. Kubo K, Ohgo K, Takeishi R, Yoshinaga K, Tsunoda N, Kanehisa H, Fukunaga T. Effects of isometric training at different knee angles on the muscle-tendon complex in vivo. Scand J Med Sci Sports 16: 159–167, 2006.
20. Lamontagne A, Malouin F, Richards CL. Viscoelastic behavior of plantar flexor muscle-tendon unit at rest. J Orthop Sports Phys Ther 26: 244–252, 1997.
21. Magnusson SP, Aagard P, Simonsen E, Bojsen-Moller F. A biomechanical evaluation of cyclic and static stretch in human skeletal muscle. Int J Sports Med 19: 310–316, 1998.
22. Magnusson SP, Simonsen EB, Aagaard P, Boesen J, Johannsen F, Kjaer M. Determinants of musculoskeletal flexibility: Viscoelastic properties, cross-sectional area, EMG and stretch tolerance. Scand J Med Sci Sports 7: 195–202, 1997.
23. Magnusson SP, Simonsen EB, Aagaard P, Kjaer M. Biomechanical responses to repeated stretches in human hamstring muscle in vivo. Am J Sports Med 24: 622–628, 1996.
24. Magnusson SP, Simonsen EB, Aagaard P, Sorensen H, Kjaer M. A mechanism for altered flexibility in human skeletal muscle. J Physiol 497: 291–298, 1996.
25. McHugh MP, Nesse M. Effect of stretching on strength loss and pain after eccentric exercise. Med Sci Sports Exerc 40: 566–573, 2008.
26. McNair PJ, Dombroski EW, Hewson DJ, Stanley SN. Stretching at the ankle joint: Viscoelastic responses to holds and continuous passive motion. Med Sci Sports Exerc 33: 354–358, 2001.
27. Mense S, Stahnke M. Responses in muscle afferent fibres of slow conduction velocity to contractions and ischaemia in the cat. J Physiol 342: 383–397, 1983.
28. Morse CI, Degens H, Seynnes OR, Maganaris CN, Jones DA. The acute effect of stretching on the passive stiffness
of the human gastrocnemius muscle tendon unit. J Physiol 586: 97–106, 2008.
29. Nelson AG, Guillory IK, Cornwell C, Kokkonen J. Inhibition of maximal voluntary isokinetic torque production following stretching is velocity-specific. J Strength Cond Res 15: 241–246, 2001.
30. Ogura Y, Miyahara Y, Naito H, Katamoto S, Aoki J. Duration of static stretching
influences muscle force production in hamstring muscles. J Strength Cond Res 21: 788–792, 2007.
31. O'Sullivan K, Murray E, Sainsbury D. The effect of warm-up, static stretching
and dynamic stretching on hamstring flexibility in previously injured subjects. BMC Musculoskelet Disord 10: 37, 2009.
32. Perrier ET, Pavol MJ, Hoffman MA. The acute effects of a warm-up including static or dynamic stretching on countermovement jump height, reaction time, and flexibility. J Strength Cond Res 25: 1925–1931, 2011.
33. Ryan ED, Beck TW, Herda TJ, Hull HR, Hartman MJ, Costa PB, Defreitas JM, Stout JR, Cramer JT. The time course of musculotendinous stiffness
responses following different durations of passive stretching. J Orthop Sports Phys Ther 38: 632–639, 2008.
34. Siatras TA, Mittas VP, Mameletzi DN, Vamvakoudis EA. The duration of the inhibitory effects with static stretching
on quadriceps peak torque production. J Strength Cond Res 22: 40–46, 2008.
35. Van Gelder LH, Bartz SD. The effect of acute stretching on agility performance. J Strength Cond Res 25: 3014–3021, 2011.
36. Williams C. Flexibility training: Incorporating all components of fitness. NSCA Perform Train J 10: 11–14, 2011.
37. Winchester JB, Nelson AG, Kokkonen J. A single 30-s stretch is sufficient to inhibit maximal voluntary strength. Res Q Exerc Sport 80: 257–261, 2009.
38. Wyon M, Felton L, Galloway S. A comparison of two stretching modalities on lower-limb range of motion measurements in recreational dancers. J Strength Cond Res 23: 2144–2148, 2009.
39. Yamaguchi T, Ishii K. Effects of static stretching
for 30 seconds and dynamic stretching on leg extension power. J Strength Cond Res 19: 677–683, 2005.
Keywords:Copyright © 2013 by the National Strength & Conditioning Association.
static stretching; muscle flexibility; stiffness; isokinetic dynamometer; healthy subjects