Effect of switching the control direction on force control using isometric leg extension

Abstract

 In this study, we investigated the effects of differing control processes on the duration of zero-velocity in force control and force level control accuracy and quickness using isometric leg contraction tasks. Eleven participants were instructed to adjust the target force from 20% maximal voluntary contraction (MVC: 20% task) or from 60%MVC (60% task) to 20%, 40%, or 60%MVC after relaxing completely. The participants were instructed to control their force as quickly and as accurately as possible on receiving a visual stimulus, and the force produced by the participants was recorded. We investigated the differences in the task (20% or 60%MVC) and target (20%, 40%, or 60%MVC) force levels. We found that the target force level in the 20% task was higher than during the other target force levels for both tasks. The duration of zero-velocity was longer during the 60% task than in the 20% task for all target force levels. Before and after the period of zero-velocity, relaxation and re-adjustment time were longer during the 60% task than during the 20% task for all target force levels. Furthermore, the re-adjustment time was longer in the 60% task than in the 20% task for all target force levels; re-adjustment time was also found increase successively for the 20%, 40% and 60% MVC target force levels. Therefore, our findings suggest that during control the slight magnitude, accurate control of the force was difficult, irrespective of the magnitude of the force before relaxing completely. Moreover, the duration of zero-velocity became longer with greater magnitudes of force before relaxing completely, which affected the quickness at which force control was achieved after switching the control direction.