Pointing to a target from an upright standing position: anticipatory postural adjustments are modulated by the size of the target in humans

To examine the influence of the target size onto postural ENIG activity, eight subjects performed, from a standing position, rapid and accurate pointings to a target located within reach. The target size was varied across blocks of trials. Hand movement time increased when the target size was decreased. Interestingly, the magnitude of the integrated EMG activity of lower limb muscles (TAi, TFLc, RFi) decreased with a decreasing target size, while that of the erector spinae increased. The effects were observed as early as 200 ms before the hand movement onset. When standing, these early commands could influence the control of the hand during the acceleration phase. The target size was specified within the postural command before any hand movement took place suggesting the characteristics of the pointing task were integrated in a feedforward manner. (C) 2004 Elsevier Ireland Ltd. All rights reserved.