Joint torques are associated with speed-accuracy trade-offs during human reaching movements

Abstract

Fitts' law is an empirically derived model that describes movement duration during human arm reaching as a function of movement distance and target width. Although this law does not consider dynamic properties, such as motor commands and joint torques, it can explain the speed-accuracy trade-off characteristics of human arm movements in most cases. However, human arm movements are achieved by transforming motor commands through dynamics. Thus, speed-accuracy trade-off characteristics can be explained by the joint torque produced by motor commands. Here, we investigated whether the speed-accuracy trade-off described by Fitts' law can be better explained by joint torque, which is directly controlled by motor commands. To examine the relationships between the movement speed, end-point accuracy, and joint torque, we performed temporally and spatially constrained experiments. A positive correlation was observed between the integrated absolute torque and end-point error, which is a measure of end-point accuracy for the trial-averaged values of each experimental condition. These findings suggest the possibility that the speed-accuracy trade-off described by Fitts' law can be explained by human arm dynamics and its parameters.