EXCESSIVE STRETCHING REDUCES MUSCLE ELASTICITY

Hoge, K. M., Ryan, E. D., Herda, T. J., Costa, P. B., Walter, A. A., Beck, T. W., Stout, J. S., & Cramer, J. T. (2009). Acute effects of passive ACSM 56th Annual Meeting, Seattle, Washington. stretching on the electromechanical delay. Presentation number 1993.

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"The electromechanical delay (EMD) is the latency between muscle stimulation and its resultant force production. The EMD may be influenced by the excitation-contraction coupling process and the muscle’s series elastic component (SEC). If a bout of stretching affects the SEC, then it may affect the EMD."

This study examined the acute effects of passive stretching on the electromechanical delay. Male volunteers (N = 16) had each foot was stabilized in a custom-built apparatus designed to measure plantar flexion force with a knee joint angle of 180° and ankle joint angle of 90°. The apparatus was also attached to a Biodex System 3 dynamometer that stretched the plantar flexor muscles by passively dorsiflexing the foot at 5°/sec until a constant-torque threshold was achieved and held at a point of discomfort. Nine repetitions of each stretch were held for 135 seconds with 10 seconds of rest between repetitions. Before and after stretching, a supramaximal stimulus was applied to the tibial nerve in the popliteal fossa. Twitch force was recorded from a load cell, while EMG signals were recorded from the soleus and gastrocnemeus muscles.

There was an 11.2% increase electromechanical delay from pre- to post-stretching.

Implication. Twenty minutes of constant-torque passive stretching increased the electromechanical delay of the plantar flexor muscles, which may have reflected stretching-induced changes in the series elastic component. Excessive stretching reduces the elastic properties of muscles and their supporting structures.

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