Effects of graded levels of exercise on ipsilateral and contralateral post-exercise resting rectus femoris mechanomyography

Mechanomyography has shown that “resting” muscle is mechanically active, with greater activity after vigorous exercise. This experiment studied the post-exercise resting mechanomyography activity that results from different levels of exercise; the effects of exercise levels on the contralateral non-exercised limb; and the effects of resting muscle length on post-exercise resting mechanomyographic activity. Ten healthy volunteers had mechanomyography recordings over both mid-rectus femoris, at rest, before and after sets (1, 5, 10, 20, and 30 repetitions) of right leg extensions on an isokinetic dynamometer at 60 s⁻¹. Sets were performed a week apart, after only sedentary activity during the previous two hours. No definite threshold effect was shown. There was a linear correlation between mechanomyography and work done (R = 0.61, P < 0.01). There was a positive correlation of change of activity between the two thighs (R = 0.62, P < 0.01), with the non-exercised thigh demonstrating about half the activity of the exercised thigh. Finally, we observed that mechanomyographic activity was greater when rectus femoris muscle length was shorter (i.e. when the leg was extended versus flexed). We conclude that resting mechanomyography increases with increasing work and that there is a cross-over for increase in mechanomyography in the non-exercised leg, suggesting a neural mechanism. The greater mechanomyographic activity at shorter muscle lengths suggests that muscle that is less stretched could more freely oscillate, producing higher MMG amplitudes. Altered activity of the muscle spindle gamma loop or Golgi tendon apparatus may also play a role in altered activity with different muscle length.