Consecutive postural adjustments (CPAs): A kinetic analysis of variable velocity during a pointing task

This paper examines the postural adjustments that occur after the end of a voluntary movement (consecutive postural adjustments, CPAs). Its aim is to reinforce the theory that CPAs are necessary to counterbalance the destabilizing effect of a voluntary movement. In addition, we compared the main features of CPAs with those of anticipatory postural adjustments (APAs) in order to gather evidence that could afford new insights into postural programming.

Nine healthy adults were invited to adopt a sitting position to perform nine pointing movements at decreasing velocities. The antero-posterior component of the reaction forces was measured. Upper limb kinematics were recorded and the kinetics calculated. The main features under study included linear impulses, peak amplitudes and duration of CPAs and APAs.

Two main results emerged from our study: the impulse produced after the end of a focal movement (CPAI_x) was negative, while the impulse produced before its end (^*ASPI_x) was positive; their absolute values were not significantly different; when movement velocity increased, CPA impulse and peak amplitude (pCPA) increased significantly, contrary to duration (dCPA). Furthermore, APA impulse, peak amplitude and duration were all increased.

These findings on pointing movements strengthen the hypothesis that CPAs play a role of body stabilization and that the postural chain kinetics is programmed according to focal movement velocity. Evidence on CPA obtained from healthy subjects may contribute to the further specification of the differences associated with motor impairment.