Variability in cross-modal proprioceptive judgements impairs 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, and muscle strength). A total of 184 healthy individuals (18-95 yr; 98 females and 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 generalized 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-yr-old required on average 13 s longer than a 60-yr-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.NEW & NOTEWORTHY This is the first study to estimate the effect of proprioception on upper-limb function across the lifespan within an explicitly defined causal framework. Specifically, we investigated whether deficits in low-level proprioceptive judgements (made within a single frame of reference) or high-level proprioceptive judgements (made between frames of reference) impair upper-limb function across the lifespan. We provide novel evidence that imprecise high-level proprioceptive judgements impair an everyday upper-limb functional task, with this relationship strengthening with age.