Inhibition of electromyographic activity in human triceps surae muscles during sinusoidal rotation of the foot.

Torque and electromyographic (EMG) responses to sinusoidal rotations of the foot were measured. The frequency range of the movements was 0.5 Hz to 15 Hz at amplitudes ranging between 1 and 10 degrees. At frequencies above 7 Hz, the EMG activity did not follow individual foot rotation cycles. The EMG activity was inhibited whenever the peak torque was large with respect to the first cycle peak torque. Dantrolene sodium reduced the torque developed in triceps surae, allowing the EMG activity to follow individual stretch cycles. As the drug was metabolized, the EMG activity returned to the character seen in the pre-drug control--that is, inhibition on alternate stretch cycles. It is concluded that the EMG inhibition phenomenon can be attributed in part to force receptors in muscle but that these receptors are not the sole contributors to the inhibition.