Adaptive changes in balance control strategies under continuous exposure to visual-somatosensory conflicts.

Human postural control system has the capacity to adapt to balance-challenging perturbations. However, the characteristics and mechanisms of postural adaptation to continuous perturbation under the sensory conflicting environments remain unclear. We aimed to investigate the functional role of oscillatory coupling drive to lower-limb muscles with changes in balance control during postural adaptation under multisensory congruent and incongruent environments. We combined a platform moving sinusoidally (0.24 Hz) along the anterior-posterior (AP) axis and a virtual scene moving sinusoidally (0.24 Hz) either along the AP or the medio-lateral (ML) axis to present a 3-min visual-somatosensory congruent condition (n = 10) or incongruent condition (n = 12), respectively. We analyzed the kinematic data and performed intermuscular coherence analysis of surface EMG data from bilateral lower limbs. We found that the inter-limb coherence was larger under the congruent condition and decreased over the 3-min perturbation, while inter-limb coherence remained low and showed no changes under the incongruent condition over the 3-min perturbation. These results suggest that exposure to the incongruent condition disrupted inter-limb intermuscular coupling. Besides, we found the bilateral intra-limb coherence decreased over 3-min congruent and incongruent perturbation, with the bilateral ankle joint angular velocity decreased and the coupling strength (0.2-0.3 Hz) between whole body sway and sinusoidal stimuli in AP decreased. These findings suggest that continuous exposure to sinusoidal perturbation in AP under congruent and incongruent conditions decreased bilateral intermuscular coupling, contributing to flexibility in the sagittal plane. Overall, we suggested the postural control system adapts context specifically to different sensory environments, with distinct characteristics of neuromuscular control strategies.NEW & NOTEWORTHY Lower limb muscle coordination plays a vital role when facing continuous perturbation by updating sensorimotor mappings. However, it is unclear how muscle coordination adapts to visual-somatosensory congruent and incongruent perturbations. Here, we found that muscle coordination showed context-specific adaptive changes to visual-somatosensory congruent or incongruent environment.