STUDY DESIGN: Repeated-measures experimental design. OBJECTIVE: To examine the acute effects of different durations of passive stretching on the time course of musculotendinous stiffness (MTS) responses in the plantar flexor muscles. BACKGROUND: Stretching is often implemented prior to exercise or athletic competition, with the intent to reduce the risk of injury via decreases in MTS. METHODS AND MEASURES: Twelve subjects (mean ± SD age, 24 ± 3 years; stature, 169 ± 12 cm; mass, 71 ± 17 kg) participated in 4 randomly-ordered experimental trials: control with no stretching, 2 min (2_min), 4 min (4_min), and 8 min (8_min) of passive stretching. The passive-stretching trials involved progressive repetitions of 30-second passive stretches, while the control trial involved 15 minutes of resting. MTS assessments were conducted before (prestretching), immediately after (poststretching), and at 10, 20, and 30 minutes poststretching on a Biodex System 3 isokinetic dynamometer. RESULTS: MTS decreased (P<.05) immediately after all stretching conditions (2_min, 4_min, and 8_min). However, MTS for the 2_min condition returned to baseline within 10 minutes, whereas MTS after the 4_min and 8_min passive-stretching conditions returned to baseline within 20 minutes. CONCLUSIONS: Practical durations of passive stretching resulted in significant decreases in MTS; however, these changes return to baseline levels within 10 to 20 minutes. LEVEL OF EVIDENCE: Level 5.

J Orthop Sports Phys Ther. 2008;38(10):632-639, published online 11 July 2008. doi:10.2519/jospt.2008.2843  

KEY WORDS: compliance, passive, stiffness, strain injury, stretch

STUDY DESIGN: Repeated-measures experi­mental design. OBJECTIVE: To examine the acute effects of static stretching on peak torque, the joint angle at peak torque, mean power output, and electromyo­graphic and mechanomyographic amplitudes and mean power frequency of the vastus lateralis and rectus femoris muscles during maximal eccentric isokinetic muscle actions. BACKGROUND: A bout of static stretching may impair muscle strength during isometric and concentric muscle actions, but it is unclear how static stretching may affect eccentric force production. METHODS AND MEASURES: Fifteen men (mean 6 SD age, 23.4 6 2.4 years) performed maximal eccentric isokinetic muscle actions of the dominant and nondominant knee extensor muscles at 60°·s–1 and 180°·s–1 on an isokinetic dynamometer, while electromyographic and mech­anomyographic amplitudes (root-mean-square) and mean power frequency were calculated for the vastus lateralis and rectus femoris muscles. Peak torque (Nm), the joint angle at peak torque (°), and mean power output (W) values were recorded by the dynamometer. Subsequently, the dominant lower extremity knee extensors underwent static stretching exercises, then the assessments were repeated. RESULTS: There were no stretching-related changes in peak torque, the joint angle at peak torque, mean power output, electromyographic or mechanomyographic amplitude, or mean power frequency (P>.05). However, there were expected velocity-related, limb-related, and muscle-related differences (P≤.05) that were unrelated to the stretching intervention. CONCLUSION: These results suggest that static stretching does not affect maximal eccentric isokinetic torque or power production, nor does it change muscle activation.  

J Orthop Sports Phys Ther. 2007;37(3):130-139. doi:10.2519/jospt.2007.2389 

KEY WORDS: EMG, muscle activation, muscle stiffness, stretching-induced force deficit