The effect of biofeedback through posturography and the visual contribution on muscle activity and postural sway in orthostasis

Abstract

Introduction: Visual biofeedback is widely used to improve postural balance by reducing body sway. However, individuals vary in their ability to decrease sway when using visual cues, suggesting that some may not rely heavily on visual information to regulate posture. A key question is whether visually dependent individuals adopt different postural strategies compared with those who are not visually dependent when performing biofeedback tasks. This study investigated the influence of visual dependence on muscle activity and postural sway in young adults during upright stance under different visual biofeedback tasks. Methods: Nineteen adults performed four 60-second postural tasks: (1) eyes open (EO), serving as the control condition; (2) eyes closed (EC); (3) center of pressure (CoP) biofeedback with 2-cm and 4-cm targets; and (4) biofeedback using a laser pointer controlled by the right wrist. Surface electromyography (EMG) was recorded from the right tibialis anterior (TA) and medial gastrocnemius (GM), and CoP displacement was measured in the anteroposterior (AP) and mediolateral (ML) directions. A percentage-difference index of CoP sway area between EO and EC was used to classify participants as visually dependent or non-visually dependent. The Friedman test followed by Wilcoxon post-hoc comparisons was applied (α = 5%). Results: In the overall sample, TA RMS amplitude was higher during the laser biofeedback task (p = 0.010) and during the 2-cm (p = 0.012) and 4-cm (p = 0.041) target tasks compared with EO. GM RMS did not differ across conditions (p = 0.973). AP CoP standard deviation increased during CoP biofeedback regardless of target size (p < 0.05) and during the laser task (p = 0.049). CoP sway area also increased in the 4-cm target (p = 0.004) and laser (p = 0.005) conditions. Among visually dependent individuals, TA activity increased during the 2-cm target task (p = 0.047), and CoP displacement was higher during the laser task compared with EO. Among non-visually dependent participants, TA and GM showed no differences across conditions, but AP standard deviation and sway area decreased during the 2-cm and 4-cm target tasks and increased during laser biofeedback (p < 0.05) relative to EO. Conclusion: Postural adaptations to CoP biofeedback depend on individual visual dependence and on the biofeedback protocol applied. Visually dependent individuals tend to increase muscle activation when required to reduce postural sway, particularly with smaller targets (2 cm). In contrast, non-visually dependent individuals reduce sway without additional muscular effort. Visual dependence did not influence responses to laser biofeedback, as both groups showed greater CoP variability in this condition. These findings highlight the importance of considering visual dependence when designing biofeedback-based interventions aimed at reducing postural sway, since visually dependent individuals may exhibit greater muscular demand in response to stability-oriented tasks.