The influence of age and physical activity on the ability to use position and force feedback.

The degradation of position and force feedback and associated processing are assumed to play a significant role in the well-known deterioration of motor performance with increasing age. In older individuals, participation in physical activity has been shown to attenuate age effects on lower limb position sense. This work investigated the influence of age (young and older adults) and physical activity in older adults on the utilization of position and force feedback in upper limb matching tasks which varied in terms of demands associated with interhemispheric transfer, memory retrieval and whether the reference was provided by the same or opposite limb. Position and force matching errors increased with task demands and were greater for right than left limb matching when the opposite limb provided the reference. These effects were strongly accentuated by age. In older individuals, participation in physical activity was shown to attenuate these differences. Based on energy expenditures, active older individuals showed smaller position errors and performed movements more smoothly than the sedentary, however force-matching errors were similar for these groups. Improvements in matching performance were more pronounced when older individuals were classified according to the proportion of time spent performing tasks specific to the upper limbs compared to overall activity. The following interpretations were proposed. A predominant role of changes affecting the central nervous system and more particularly the sensorimotor memory was suggested to explain declines of position sense and the sense of muscle effort with age. Asymmetries in right/left matching performance seem to be associated with differences in the relationship between motor activity and the associated perception for each limb\hemisphere system. The results also suggest that the sense of muscle effort is primarily associated with the efference copy and may be updated by peripheral sensory information. The benefit of specific activity over general aerobic exercise may be associated with task-dependent cortical plasticity and preservation of sensorimotor memory through deliberate practice over the course of a lifetime.PhDBiological SciencesGerontologyHealth and Environmental SciencesKinesiologyPhysiologySocial SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126877/2/3287439.pd