Unstable-surface squats are associated with lower postural stability indices but not interlimb sway asymmetry in healthy young adults

Unstable-surface exercise is commonly used to challenge postural control; however, the acute responses of postural stability and interlimb sway asymmetry to unstable-surface squats remain unclear. To examine postural stability and interlimb sway asymmetry under stable- and unstable-surface squat conditions in healthy young adults. Thirty-three healthy young adults completed three conditions: baseline (no squats), 30 bodyweight squats on a stable surface, and 30 bodyweight squats on an unstable surface. The squat conditions were randomized, whereas the baseline condition was performed first for all participants. Postural stability and interlimb sway asymmetry were assessed using the Biodex Balance System. Differences between conditions were analyzed using repeated-measures ANOVA with Holm-adjusted post-hoc comparisons. The Overall Stability Index was lower in the unstable-surface squat condition compared with baseline (5.95 ± 2.52 vs. 4.70 ± 2.08, p = .01), whereas no significant difference was observed between baseline and the stable-surface squat condition (5.21 ± 2.49). Similarly, the Overall Sway Index was lower in the unstable-surface squat condition compared with baseline (6.79 ± 2.69 vs. 5.48 ± 2.41, p = .01), with no significant difference observed after stable-surface squats (5.73 ± 2.68). Condition-related differences were also observed in anterior–posterior stability and sway, with lower values in the unstable-surface condition compared with baseline. No significant differences were observed in medial–lateral stability or sway. Interlimb sway asymmetry indices remained unchanged across conditions. The unstable-surface squat condition was associated with lower postural stability and sway index values, particularly in the anterior–posterior direction, compared with baseline, whereas the stable-surface squat condition showed no significant differences. No significant changes were observed in interlimb sway asymmetry. Given that baseline testing was performed first and no within-session pre-exercise measurements were collected, these findings should be interpreted as condition-related associations rather than definitive causal effects of squat exercise. ClinicalTrials.gov Identifier: https://clinicaltrials.gov/study/NCT07341555, registered on January 6, 2026. A single bout of unstable-surface squats was associated with lower overall and anterior–posterior postural stability indices in healthy young adults. Stable-surface squats were not associated with significant acute changes in postural stability compared with baseline. Neither stable- nor unstable-surface squats were associated with significant changes in interlimb sway asymmetry during single-leg stance. Unstable-surface squats may represent a potential acute warm-up strategy for modifying postural control responses.