Figure 1.

Sample recordings from a representative subject. Rectified and integrated average recordings of EMG in Flexor Carpi Radialis (FCR, prime mover), Biceps Brachii (BB), Triceps Brachii (TB), Anterior Deltoid (AD), together with wrist flexion, elbow excursion and ensuing final position of pen-tip. Time 0 = FCR onset. When pointing with the preferred wrist (upper panels), the right elbow equilibrium was preserved thanks to excitatory APAs in TB and inhibitory APAs in BB and AD, which precede the FCR activation by about 65 ms. In the non-preferred side (lower panels) APAs were delayed, indeed they advanced the prime mover onset by just 20–30 ms. This was associated with an increase of the elbow excursion during the wrist movement. The effect that the different APA timing and the associated elbow stabilization had on the pen-tip final position is shown on the right-lowermost panels.