Test–retest reliability of postural sway measures using a portable low-cost force plate in healthy adultsVindiš, Miha (Avtor) Kozinc, Žiga (Avtor) Nedović, Nenad (Avtor) balancereliabilityforce plateBackground and Purpose Center of pressure (CoP) metrics derived from force plates are widely used to quantify postural control, but laboratory-grade systems limit routine clinical and field implementation. Portable low-cost force plates could enable physiotherapists to monitor balance longitudinally, provided that their measurements are sufficiently reliable and clinically interpretable. This study addresses a gap in the literature by systematically comparing the test–retest reliability of CoP outcomes across bipedal and single-leg stance conditions using a portable low-cost force plate, providing device-specific and task-specific validation data relevant to clinical and field-based implementation. Methods This test–retest reliability study included 27 healthy young adults who completed two laboratory sessions 7–10 days apart. In each session, participants performed three 30-s trials of bipedal quiet stance and three 30-s trials of single-leg stance on each leg barefoot with standardized arm position and visual fixation. Mean values across repetitions were analyzed. Relative reliability was assessed using two-way mixed-effects ICC for absolute agreement (3,1), with 95% confidence intervals. Absolute reliability was quantified using typical error (TE) and coefficient of variation (CV). Paired t-tests evaluated systematic between-session differences. Results Across all outcomes, single-leg stance demonstrated substantially higher inter-session reliability compared to bipedal stance. Measures of total CoP displacement and velocity during single-leg stance exhibited good to excellent reliability (ICC = 0.85–0.90) and low absolute error (CV ≈ 8%), with direction-specific displacements showing similarly consistent results (ICC = 0.83–0.90; CV generally < 10%). In contrast, the CoP ellipse area and standard deviation measures were considerably less stable (ICC = 0.57–0.79) and displayed markedly higher variability (CV ≈ 16%–23%). The contrast was even more pronounced in the bipedal stance, where reliability was poor to moderate across all parameters (ICC = 0.39–0.65), with the ellipse area exhibiting excessive variability (CV > 60%). Notably, no systematic between-session differences were observed for most outcomes, further supporting the consistency of the measurements. Discussion In healthy young adults, single-leg stance provides more reliable CoP measures than bipedal quiet stance when using a portable low-cost force plate. Displacement- and velocity-based outcomes during single-leg stance appear most suitable for repeated assessments and monitoring. MDC95 values should be interpreted strictly as measurement-error thresholds and not as indicators of clinical responsiveness or meaningful clinical change because responsiveness was not evaluated.20262026-07-08 18:19:33Članek v reviji23287UDK: 612.76ISSN pri članku: 1471-2865DOI: 10.1002/pri.70270COBISS.SI-ID: 284112387sl