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 minutes (2min), 4 minutes (4min), and 8 minutes (8min) 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 (2min, 4min, and 8min). However, MTS for the 2min condition returned to baseline within 10 minutes, whereas MTS after the 4min and 8min 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.
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Ryan et al. (2008) studied this question.