Metric-Specific Differences and Similarities in Center-Of-Pressure Sway Area Across Visual Conditions During Single-Leg Stance

This study compared a new center-of-pressure (COP) sway-area metric, the convex hull, with three traditional metrics (rectangular, 66% effective, 95% ellipse) for single-leg balance (SLB) across six visual conditions. One hundred young adults completed 10-second SLB under full vision, four graded stroboscopic-vision levels, and no vision. COP data were used to compute all four metrics. A 4 × 6 repeated-measures ANOVA showed a significant interaction (F = 8.596, p < .001). Rectangular areas consistently produced the largest values, whereas 66% effective areas produced the smallest. The convex hull and 95% ellipse did not differ significantly but were strongly correlated (r = 0.924–0.978), despite a small positive bias. All metrics distinguished among full-, partial-, and no-vision states; however, only the convex hull detected an additional difference between two partial-vision levels, indicating potential sensitivity to subtle changes in postural control. These findings suggest metrics are not interchangeable and the convex hull and 95% ellipse may offer more balanced assessments.