Precision-Dependent Changes in Motor Variability During Sustained Bimanual Reaching.

Movement variability of the upper limb was investigated using a bimanual Fitts' task. Participants tapped rhythmically between target-pairs of different index of difficulties for three intervals of 20 min each. We studied the effects of index of difficulties and time-on-task on movement time, end-point variability, approximate entropy, and standard deviation of the relative phase. Lower index of difficulties and time-on-task caused decreasing movement time and increasing end-point variability. Moreover, standard deviation of the relative phase and approximate entropy moderately increased. By looking into the long-term effects of a sustained bimanual Fitts' task, this is the first time such movement variability increase is demonstrated in multiple variability indices. The relevance of the findings for future studies on work-related musculoskeletal disorders is being discussed.