Interaction between postural asymmetry and visual feedback effects in undisturbed upright stance control in healthy adults.

Objectives: The technique of additional visual feedback has been shown to significantly decrease the center of pressure (CP) displacements of a standing subject. Body-weight asymmetry is known to increase postural instability due to difficulties in coordinating the reaction forces exerted under each foot and is often a cardinal feature of various neurological and traumatic diseases. To examine the possible interactions between additional visual feedback and body-weight asymmetry effects, healthy adults were recruited in a protocol with and without additional visual feedback, with different levels of body-weight asymmetry.

Methods: CP displacements under each foot were recorded and used to compute the resultant CP displacements (CP) and to estimate vertically projected center of gravity (CG) and CP-CG displacements. Overall, six conditions were randomly proposed combining two factors: asymmetry with three BW percentage distributions (50/50, 35/65 and 20/80; left/right leg) and feedback (with or without additional VFB).

Results: The additional visual feedback technique principally reduces CG displacements, whereas asymmetry increases CP-CG displacements along the mediolateral axis. Some effects on plantar CP displacements were also observed, but only under the unloaded foot. Interestingly, no interaction between additional visual feedback and body-weight asymmetry was reported.

Discussion: These results suggest that the various postural effects that ensue from manipulating additional visual feedback parameters, shown previously in healthy subjects in various studies, could also apply independently of the level of asymmetry.

Conclusion: Visual feedback effects could be observed in patients presenting weight-bearing asymmetries.