Ryan, E. D., Herda, T. J., Hull, H. R., Hartman, M. J., Beck, T. W., Stout, J. R., & Cramer, J. T. (2008). Time course for the effects of passive stretching on musculotendinous stiffness: A dose-response study. ACSM 55th Annual Meeting Indianapolis, Presentation Number, 1365.

This investigation examined the time course for the acute effects of two, four, and eight minutes of passive stretching on musculotendinous stiffness of the plantar flexor muscles. Healthy Ss (N = 12) performed the musculotendinous stiffness assessments before, after, and at 10, 20, and 30 minutes following the passive stretching treatment. Four randomly-ordered trials were separated by 3-7 days: (a) control, (b) two minutes of passive stretching, (c) four minutes of passive stretching, and (d) eight minutes of passive stretching. For the passive stretching trials, several 30-second consecutive passive stretches of the plantar flexors were completed in a dynamometer where the lever arm passively dorsiflexed the foot to the point of discomfort, but not pain. Each 30-second stretch was separated by 20 seconds of rest until the total time under stretch for each trial was completed. The control trial consisted of quiet resting for 15 minutes. To assess musculotendinous stiffness, the dynamometer lever arm passively dorsiflexed the foot at 5° per second until the maximum tolerable stretch was achieved and held for five seconds.

There were decreases in musculotendinous stiffness from pre- to post-stretching for the two-, four-, and eight-minute trials. There were no changes from pre- to 10, 20, and 30 minutes post-stretching for any of the stretching durations. For the control trial, there was no change in musculotendinous stiffness over all time periods. However, musculotendinous stiffness remained depressed only at 10 minutes post-stretching for the four- and eight-minute trials when compared to the control condition. Musculotendinous stiffness was greater for men than women across all joint angles, with musculotendinous stiffness increasing at each larger joint angle.

Implication. All stretching conditions resulted in a decrease in musculotendinous stiffness post-stretching, with the four- and eight-minute trial effects lasting only 10 minutes. The physiological benefits of decreased musculotendinous stiffness resulting from practical stretching durations (up to eight minutes) appear to be relatively short lived.

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