Proprioceptive Deficits in Inactive Older Adults are not Reflected in Discrete Reaching Performance

During normal healthy ageing there is a decline in the ability to control simple movements, characterised by increased reaction times, movement durations and variability. There is also growing evidence of age-related proprioceptive loss which may contribute to these impairments. However this relationship has not been studied in detail for the upper limb. We recruited 20 younger adults (YAs) and 31 older adults (OAs) who each performed 2 tasks on a 2D robotic manipulandum. The first assessed dynamic proprioceptive acuity using active, multi-joint movements towards visually presented targets, with movement constrained by the robot to a predefined path. Participants made perceptual judgements of the lateral position of the unseen arm. The second was a rapid motor task which required fast, accurate movements to the same targets in the absence of hand position visual feedback, and without constraint by the robot. We predicted that the variable proprioceptive error (uncertainty range) from Task 1 would be increased in physically inactive OAs and would predict increased movement variability in Task 2. Instead we found that physically inactive OAs had larger systematic proprioceptive errors (bias). Neither proprioceptive acuity nor bias was related to motor performance in either age group. We suggest that previously reported estimates of proprioceptive decline with ageing may be exaggerated by task demands and that the extent of these deficits is unrelated to discrete, ballistic movement control. The relationship of dynamic proprioceptive acuity with movement control in tasks which emphasise online proprioceptive feedback for performance is still unclear and warrants further investigation.