Wrist and Forearm Movements While Homing in on Precision Targets

Abstract

To determine whether people employed different movement strategies when they homed in on precision targets during repetitive tapping tasks, homing in movements were isolated for analysis. The time required to home in on the targets and the absolute magnitudes of peaks in joint velocities during homing in were calculated. In addition, the number of times that three types of corrective actions: changes in movement direction, inflections in velocity, and peaks in velocity, were made during pronation/supination and in radial/ulnar actions were counted. The number of times each type of corrective action was made was regressed against the time required for homing in. The relationships were highly linear, with correlation coefficients between 0.78 and 0.94. The implication was that corrective actions occurred at a similar mean frequency, regardless of the level of task precision and that homing in was a very active process at all levels of precision studied. The number of times any type of corrective action was taken increased significantly with increased precision (P < 0.001). The mean absolute magnitudes of pronation/supination and radial/ulnar velocities declined significantly with increased task precision (P < 0.001). However, the fact that the number of corrective actions increased with increased task precision showed that the movements toward the high precision targets were not just ‘slowed down’ versions of the movements to the low precision targets. Differences between the number of corrective actions, and the magnitudes of peak velocities for tasks of different levels of precision reflect different biomechanical stresses at the wrist and forearm for the different tasks. These differences are expected to result in different effects on shoulder muscles at different levels of precision.