EMG area scaling and velocity modulations in a spatiotemporally constrained movement

Research examining the electromyographic (EMG) burst structure of rapid discrete limb movements has led to discordant findings concerning agonist burst duration. Some research has shown that duration varies as a function of movement speed while other research has shown burst constancy. Unfortunately, much of this research may be confounded by not carefully controlling movement termination accuracy and movement time (MT). Due to these potential problems, the present study was conducted to determine the effects of strict spatiotemporal constraints on EMG characteristics of a rapid elbow flexion-extension response under two movement extent conditions across five different MTs. Results revealed that a decreased MT was accompanied by a decreased agonist (biceps) burst duration and increased agonist burst amplitude. The burst duration and amplitude both increased as the movement extent increased with MT held constant. None of three current theoretical perspectives of rapid movement control (the impulse-timing model, the speed-control system hypothesis, or the speed-sensitive strategy) could fully account for these results. Instead, a control strategy was exhibited in which moving faster was accomplished by relative scaling of burst area via concomitant expansion of burst amplitude and compression of burst duration.