Condition-specific mediolateral sway and task-dependent postural complexity in individuals with generalized joint...

Generalized joint hypermobility (GJH) features ligamentous laxity and proprioceptive deficits, which impair balance. Traditional center of pressure (COP) metrics may not fully elucidate postural instability mechanisms. Multiscale entropy (MSE) evaluates nonlinear time series complexity across scales. This study integrated linear COP and MSE metrics across task conditions to evaluate GJH static postural control and compensatory strategies.

Twenty-eight GJH and twenty-six healthy controls (all right-limb dominant) were recruited. COP data were recorded using a Kistler 3D force plate. Each participant performed double-leg, left-leg, and right-leg stances under eyes-open and eyes-closed conditions. Pairwise comparisons targeted the eyes-closed tasks. Mixed-design ANOVA examined the effects of group and condition on balance parameters (α = 0.05). Spearman correlations between COP and MSE metrics were computed for each group across all six conditions (FDR-corrected); between-group differences in correlation strength were further tested via Fisher's r-to-z transformation. Trial-to-trial reliability was assessed via ICC (2,1).

For COP metrics, ANOVA revealed significant task main effects across most parameters (P < 0.01, except LFS). Except for AP_SI (P = 0.04), no other significant main effects of group were observed (P > 0.05). Group × task interactions were not significant. Pairwise comparisons indicated that under the LEC, the GJH group showed significantly greater AP_SI and ML_Amp (FDRq <0.05) and smaller ML_SI (FDRq <0.05). For MSE metrics, significant group × task interactions (P < 0.05), group main effects and task main effects (P < 0.01) were observed across most parameters. The GJH displayed significantly higher MSE during bipedal and right-limb tasks (P < 0.05). However, these between-group differences were a descriptive pattern of attenuation with increasing task difficulty. Twenty-nine COP-MSE correlations reached FDR significance in the GJH group, versus none in healthy controls. However, direct between-group comparisons using Fisher's r-to-z transformation, FDR-corrected across all 204 COP-MSE pairs, did not identify a significant difference in correlation strength.

Individuals with young GJH showed localized, condition-specific differences in mediolateral sway during LEC and a descriptive pattern of task-dependent attenuation in postural complexity as demands increased. Combining COP parameters with MSE analysis provided complementary insights that could be captured by neither measure alone.