The purpose of this study was to investigate how children and adults control bimanual activities with the influence of kinematic variables minimized. Force and timing measures were analyzed in self-paced, isometric bimanual pinch tasks performed by 6-, 8-, 10-, 12-year-old, and adult subjects. Subjects (n = 84) performed four tasks (inphase symmetrical, antiphase reciprocal, inphase asymmetrical force-right high, inphase asymmetrical force-left high) cycling between low levels (10-30%) of maximal volitional force during three 15-s trials. Bimanual tasks requiring similar activation between the hands were performed more accurately, more quickly, and with less force and timing variability than tasks requiring different actions and/or levels of force to be produced simultaneously. Evidence of force entrainment between the hands was exhibited when force direction (increasing vs. decreasing) was similar between hands but greater relative force was required of the left hand. Lower accuracy and greater variability resulted when controlled decrement of force was required to reach the lower force targets as opposed to the upper force targets which required subjects to increase force. Subjects in the two youngest age groups exhibited lower force accuracy and greater force and timing variability relative to older children and adults. Twelve-year-old subjects approximated adults' performance in all variables.
K.B. Harbst is with the Department of Physical Therapy at the University of Wisconsin-La Crosse, La Crosse, WI 54601. J.-A.C. Lazarus is with the Department of Kinesiology at the University of Wisconsin-Madison, Madison, WI 53710. J. Whitall is with the Department of Physical Therapy at the University of Maryland, Baltimore, MD 21201.