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.
"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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