Accuracy of a wrist-pointing movement in dominant and non-dominant hand is correlated to the timing of intra-limb Anticipatory Postural Adjustments

It is a common experience to feel motor awkwardness and less accuracy when performing a movement with the non-preferred limb. Here we show that this impairment partly stems from changes in the timing of the Anticipatory Postural Adjustments (APAs) in the non-preferred side. In this aim, we investigated the effect of lateralization on APAs in Biceps Brachii (BB), Triceps Brachii (TB) and Anterior Deltoid (AD), which stabilize the arm when performing a wrist movement when pointing to a given target with a pencil (prime mover Flexor Carpi Radialis). Moreover, we analysed the elbow and wrist kinematics as well as the accuracy of the voluntary movement. The mean kinematics of wrist movement and its latency, with respect to prime mover recruitment, were similar in the two sides. APAs in TB, BB and AD were instead delayed of about 20-30 ms when comparing the non-dominant vs. dominant hand. This delay was associated with an altered fixation of the elbow, which showed a higher excursion in the non-preferred limb, and with a decreased accuracy of pointing movement performed with that limb. Present results strengthened the idea that, by securing the elbow position, an appropriate timing of APAs is fundamental for refining the voluntary movement accuracy. The linkage between APAs, elbow fixation and movement accuracy also agrees with the recent suggestion that APAs and prime mover recruitment are driven by a shared motor command, which strives to obtain an accurate pointing.