The ischemic block of the forearm abolishes index-finger's movements but not its associated APAs

The voluntary movement induces postural perturbations which are counteracted by unconscious feed-forward motor activities, known as anticipatory postural adjustments (APAs). Thus, for every movement, two motor commands are dispatched: one recruiting the prime mover and one driving APAs. These commands are classically thought to be separately controlled, this study investigates if they could be instead considered as a single element of the motor program. We analyzed APAs in Biceps Brachii, Triceps Brachii and Anterior Deltoid that precede an index-finger flexion. APAs and prime mover (Flexor Digitorum Superficialis) activation were recorded in three conditions: before, during and after a long lasting ischemic block of the forearm. Ischemia suppressed both the forearm sensory feed-back and the prime mover activation, thus cancelling finger flexion and the ensuing postural perturbation. Thus, a suppression of APAs should be expected, since purposeless and uneconomical. Intriguingly enough, large APAs were instead apparent without significant differences in latency and amplitude, except for Anterior Deltoid that showed smaller APAs during ischemia. The observation that APAs remain tailored to the intended movement in absence of perturbation supports the idea that postural and voluntary commands cannot be separated each other, as they both belong to an unique motor program.