Assessment of Postural Sway Area in Single-Leg Balance: A Comparative Analysis of Center-of-Pressure Area Metrics with the Convex Hull approach

Abstract

PURPOSE Quantifying postural control using Center-of-Pressure (COP) data obtained from a force plate is commonly used in balance assessments, yet the sensitivity of various sway area metrics remains unclear. This study introduced the convex hull area as a novel metric and aimed to examine how four COP-based sway area measures—rectangular, 66% effective, 95% ellipse, and the convex hull area—respond to progressively restricted visual conditions during single-leg balance. We also aimed to identify how the convex hull area performed relative to traditional sway area metrics. METHODS Forty healthy adults (20 males and 20 females) performed three 10-second single-leg balance trials on a force plate under progressively restricted visual conditions using stroboscopic goggles. Three traditional COP-based sway area parameters and the introduced convex hull area were used to quantify single-leg postural control. All participants completed the balance tests under six visual conditions. RESULTS A two-way repeated measures ANOVA revealed a significant interaction between sway area parameters and visual conditions (F=5.90, p<.001). The 95% ellipse area showed the highest sensitivity, followed by the convex hull, rectangular, and 66% effective area parameters across different visual conditions. The 95% ellipse and convex hull area produced similar results and were significantly different from the rectangular and 66% effective area (p<.001). CONCLUSIONS These findings suggest that the convex hull area is capable of detecting changes in postural control alongside the 95% ellipse area, performing comparably to traditional sway area metrics. Our results may contribute to the standardization of COP-based sway area metrics.

Keywords

• posturography
• postural control
• cop area calculation
• boundary area