Control Strategies for Accurate Force Generation and Relaxation

Abstract

Characteristics and motor strategies for force generation and force relaxation were examined using graded tasks during isometric force control. Ten female college students ( M age = 20.2 yr., SD = 1.1) were instructed to accurately control the force of isometric elbow flexion using their right arm to match a target force level as quickly as possible. They performed: (1) a generation task, wherein they increased their force from 0% maximum voluntary force to 20% maximum voluntary force (0%–20%), 40% maximum voluntary force (0%–40%), or 60% maximum voluntary force (0%–60%) and (2) and a relaxation task, in which they decreased their force from 60% maximum voluntary force to 40% maximum voluntary force (60%–40%), 20% maximum voluntary force (60%–20%), or to 0% maximum voluntary force (60%–0%). Produced force parameters of point of accuracy (force level, error), quickness (reaction time, adjustment time, rate of force development), and strategy (force wave, rate of force development) were analyzed. Errors of force relaxation were all greater, and reaction times shorter, than those of force generation. Adjustment time depended on the magnitude of force and peak rates of force development and force relaxation differed. Controlled relaxation of force is more difficult with low magnitude of force control.