Passage I

A muscle twitch (a stimulus-contraction-relaxation cycle) is divided into 3 phases (the latent period, the contraction phase, and the relaxation phase) based on the timing of the stimulus and changes in the force generated by the muscle. Table 1 shows when each phase starts and ends.

Figure 1 shows the force generated by an adductor pollicis (a thumb muscle) undergoing an isometric twitch (a twitch that does not change the muscle’s length). In Figure 1, force is given in newtons (N) and time is given in milliseconds (msec).