STATIC BUT NOT DYNAMIC STRETCHING REDUCES LEG STRENGTH

Herda, T. J., Cramer, J. T., Ryan, E. D., McHugh, M. P., &Stout, J. R. (2007). Acute effects of static versus dynamic stretching on isometric strength and neuromuscular function of the leg flexors. ACSM Annual Meeting New Orleans, Presentation Number, 2356.

This study examined the acute effects of static and dynamic stretching on peak torque, electromyography, and mechanomyography of the biceps femoris muscle during isometric maximal voluntary contractions of the leg flexors. Males (N = 14) performed two isometric leg flexion maximal voluntary contractions at four randomly ordered knee joint angles (41, 61, 81, and 101 below full extension). Electromyography and mechanomyography signals were recorded from the biceps femoris muscle. Torque values were sampled from an isokinetic dynamometer. The right hamstrings were stretched for approximately nine minutes with either three static stretching exercises with four repetitions, each lasting ~30 seconds, or four sets of three dynamic stretching exercises (12-15 repetitions) with each set lasting ~30 seconds.

Peak torque decreased significantly after static stretching at 81 and 101 but not at the other angles. There were no changes in peak torque after dynamic stretching. Normalized electromyography amplitudes remained unchanged after the static stretching, but increased after the dynamic stretching at 101 and 81. The static stretching caused an increase in normalized mechanomyography amplitudes at 101, while the dynamic stretching increased mechanomyography amplitudes at all joint angles.

The increases in electromyography and mechanomyography amplitudes after dynamic stretching may reflect increases in muscle temperature and/or potentiating effects of the dynamic stretching exercises that were independent of muscle strength. The increases in mechanomyography amplitude following the static stretching may have reflected increases in active musculotendinous compliance that coincided with the decreases in hamstring strength.

Implication. Static stretching reduced hamstring strength at the two shortest muscle lengths, but strength was unaltered by dynamic stretching.

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