Effects of control direction on the accuracy of force control

In this study, we investigated the effects of control direction on the control of the force output level accurately and quickly through isometric leg contraction tasks. Ten subjects were instructed to adjust the target force to 20% MVC (20% task) or 60% MVC (60% task). These tasks were performed under three conditions: a direct condition where the subject controlled the force from 0% MVC, a changing condition where the subject controlled the force from 20% MVC (small amount), and a changing condition where the subject controlled the force from 60% MVC (large amount) after relaxing completely. Using visual stimulus, subjects were instructed to control their force output as quickly as and as accurately as possible. The forces produced by the subjects were recorded. Results show that for the 20% task, it was difficult to accurately control the force under changing conditions as opposed to a discrete condition, while consecutive conditions exhibited greater force control velocity than the direct condition. Therefore, our findings suggest that when controlling the force before relaxing completely, accurate control of the force became more difficult with increasing force magnitude