THE CHANGES IN EMG AND STEADINESS WITH VARIATION IN MOVEMENT SPEED DIFFER FOR CONCENTRIC AND ECCENTRIC CONTRACTIONS

The activation of muscle by the nervous system differs for concentric and eccentric contractions (Enoka & Fuglevand, 2001). These differences appear to involve both the descending command (Aagaard et al. 2000; Semmler et al. 2000) and movement-related sensory feedback (Burke et al. 1978; Schieber & Thach, 1985). Because the relative contribution of sensory feedback declines with movement speed, fast contractions are largely determined by the descending command. We asked the question, does the difference in muscle activation between concentric and eccentric contractions change with movement speed? The purpose of the study was to compare the changes in muscle activation and steadiness with variation in the speed of movement for concentric and eccentric contractions.