The effects of predictability on inter-limb postural synchronization prior to bouts of postural instability

Anticipatory balance control optimizes balance reactions to postural perturbations. Predictive control is dependent on the ability of the central nervous system to modulate gain in accordance with specific task demands. Inter-limb synchronization is a sensitive measure of individual limb contributions to balance control and may reflect the coordination of gain modulation in preparation for instability. The purpose of the study was to determine whether gain modulation in advance of predictable bouts of instability was reflected in the extent of inter-limb synchronization. Two adjacent force plates were used to collect center of pressure (COP) data from 12 healthy young adults (27.5±3.4 years). Participants prepared for internal and external balance perturbations using a cueing paradigm with three auditory warning tones followed by an imperative tone. Perturbations were delivered in blocked and randomized conditions with two perturbation magnitudes (small and large). Inter-limb synchrony was calculated using the cross-correlation function of the COP excursions from the left and right foot for three seconds prior to perturbation onset in the anteroposterior (AP) and mediolateral (ML) direction. Inter-limb synchrony decreased in the AP and ML directions as perturbation magnitude became more unpredictable. The need to take a step or not knowing whether a step was required prior to postural instability reduced ML inter-limb synchrony. No differences were found between internal and external perturbations. Modulation of postural set was evident in the extent of inter-limb synchrony.