The relationship between force control strategy and performance for force generation and relaxation

In this study, we elucidated the relationship between force control strategy and performance for force generation and relaxation in isometric arm and leg contraction tasks. Ten participants were instructed to performed the following two tasks: (1) a generation task, wherein they increased their force from 0% maximum voluntary force (MVF) to 20% MVF (0%-20%), 40% MVF (0%-40%), or 60% MVF (0%-60%), (2) and a relaxation task, in which they decreased their force from 60% MVF to 40% MVF (60%-40%), 20% MVF (60%-20%), or to 0% MVF (60%-0%). They were instructed to control their force as quickly as and as accurately as possible on visual stimulus. For each task, the produced force was recorded. We used the 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) for data analyses. The results were divided into two patterns by the form of each force wave. Parameters were analyzed between the patterns using a Mann-Whitney U test. The result of this study showed that the errors of the pulse width control strategy were greater than that of the pulse height and width control strategy for both generation and relaxation task. As for adjustment time, pulse width control strategy was longer than pulse height and pulse width control strategy for force generation, and vice versa for force relaxation. Therefore, our findings suggest that the pulse height and width control strategy was the superior in accuracy and quickness for force generation, while the pulse height and width control strategy was the superior in accuracy and the pulse width control strategy was the superior in quickness for force relaxation