Variability in cross-modal proprioceptive judgements impair upper limb function across the lifespan

Proprioceptive deficits are thought to contribute to age-related decline in upper-limb function. We aimed to estimate the effect of proprioceptive ability on upper-limb function under an explicitly specified causal framework, and to determine whether this effect varied with age. A causal graph was developed to outline plausible relationships among proprioceptive ability, upper-limb function, and related factors (e.g. age, tactile acuity, cognition, muscle strength). A total of 184 healthy individuals (18-95 years; 98 females, 86 males) completed a test battery. Proprioception was assessed using grasp-based measures of low-level proprioception (judgements within a single reference frame) and high-level proprioception (judgements across different frames of reference, involving transformations between visual and proprioceptive information). The causal graph identified the minimal adjustment set to reduce bias, and generalised linear models were used to estimate the effect of proprioceptive accuracy and precision on upper-limb function under the assumed causal structure. Poor high-level proprioception precision was linked with impaired performance on a functional task requiring participants to put on and button up a shirt, with the effect increasing with age. For example, at the median precision value, an 80-year-old required on average 13 seconds longer than a 60-year-old to complete the task. No evidence was found for an effect of low-level proprioception on functional performance. Although effect sizes were generally modest, the observed associations were consistent and demonstrated age-dependent effects. These findings are consistent with a role for high-level proprioception in upper-limb function and provide normative data across the lifespan, highlighting proprioception as a potential therapeutic target to mitigate age-related functional decline.