Fig. 2.

Representative data depicting the upward force evoked in the right elbow flexors (A) by an NMES protocol [∼10% maximal voluntary contraction (MVC) force, 40 Hz, and pulse width of 0.2 ms], force exerted by the left elbow flexors during a voluntary contraction (B), the interference EMG signal for biceps brachii (C), the isolated motor unit from the short head of biceps brachii (D), and its instantaneous discharge rate with superimposed traces of its action potential (E). The motor unit had a threshold force of 8.1% MVC, an average interspike interval of 52.3 ± 3.8 ms, and a coefficient of variation for interspike interval of 35.8 ± 1.0%.