Sedentary behaviour is linked to impaired postural balance but not gastrocnemius medialis tendon properties in older adults

Abstract

Abstract Sedentary behaviour is increasingly recognised as a distinct physiological risk factor in ageing; however, its relationship with intrinsic tendon properties and postural balance remains undefined. The objective of this study was to determine whether Sedentary Behaviour is independently associated with gastrocnemius medialis tendon properties and postural balance in older adults, after accounting for physical activity. Healthy older adults ( n  = 105) completed this cross-sectional investigation. Habitual physical behaviour was quantified over 7 days using triaxial accelerometry. All participants subsequently underwent assessments of gastrocnemius medialis tendon mechanical, material, and morphological properties, with postural balance assessed in a representative subgroup ( n  = 45). Associations were examined using single and multiple linear regression, compositional data analysis, and isotemporal substitution models. Covariates were identified via univariate General Linear Model and entered using backward elimination prior to inclusion of behavioural predictors. Sedentary behaviour levels did not significantly predict gastrocnemius medialis tendon properties or balance outcomes in unadjusted models. Following covariate adjustment, Sedentary behaviour emerged as a significant negative predictor of eyes-open balance trial duration, representing the only independent SB-related effect across 18 outcome variables. Compositional analyses revealed significant model fits for multiple outcomes; however, these associations were substantially attenuated after covariate adjustment, suggesting no significant influence of Sedentary behaviour on gastrocnemius medialis tendon characteristics. Isotemporal substitution indicated small relative outcome changes (–0.71% to + 0.56%) following 10-minute behavioural reallocations. Although Sedentary behaviour pattern parameters were associated with select tendon and balance variables, most significant models were driven predominantly by covariates rather than Sedentary behaviour metrics. This study provides novel evidence that Sedentary behaviour is not independently associated with gastrocnemius medialis tendon structure and mechanics in older adults, yet is associated with poorer postural balance performance. These findings suggest that the association between Sedentary behaviour and postural balance is unlikely to be mediated by tendon degradation and instead implicate neural and motor control pathways as plausible mechanisms. Reducing sedentary time through increased physical activity may help mitigate balance deterioration and preserve functional independence with ageing.