Ryan, E. D., Cramer, J. T., Herda, T. J., Hull, H. R., Hartman, M. J., Karabulut, M., Anderson, R. L., & Stout, J. R. (2007). Time course for the acute effects of passive stretching on isometric strength and neuromuscular function. ACSM Annual Meeting New Orleans, Presentation Number, 2361.

This study examined the time course for the acute effects of eight minutes of passive stretching on isometric peak torque, percent voluntary activation, electromyography, and mechanomygraphy of the plantarflexor muscles. Ss (N = 14) performed 16 consecutive 30-s passive stretches (time under stretch was ~8 minutes) on an active isokinetic dynamometer. Isometric peak torque, percent voluntary activation, electromyography amplitude, and mechanomygraphy amplitude were assessed before, immediately after, and at 10, 20, and 30 minutes post-stretching.

There was a 9% significant decrease in isometric peak torque immediately after the stretching. It remained non-significantly depressed during all observations post-stretching. Normalized mechanomygraphy amplitudes were unchanged immediately after the stretching, but progressively increased during post-stretching. Percent voluntary activation and electromyography were unaltered.

Implication. Eight minutes of passive stretching reduced plantarflexor strength immediately after the stretching, however, most of the force deficit recovered after 10 minutes. The stretching-induced force deficit was not accompanied by decreases in muscle activation or changes in mechanomygraphy amplitude. These findings suggested that decreases in plantarflexor strength after only eight minutes of passive stretching may be attributed to increases in musculotendinous compliance, rather than decreases in muscle activation.

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