Abstract
BACKGROUND: There has been growing interest in the interrelationship between age-related reductions in cognitive and motor function. To advance the understanding of this interrelationship, we sought to determine whether a mentally fatiguing task differentially effects hand grip motor function in older versus younger adults.
METHODS: Young (n = 10, 33 ± 3 years) and older adults (n = 15, 69 ± 3 years) free of overt neurological disease and who did not report chronic fatigue symptoms participated in two testing sessions. During both sessions, participants had their composite grip strength (GS) and their multi-finger force deficit (MFFD) measured. The MFFD assays the degree of neural inactivation observed during a composite grip strength test. During one session participants completed a series of psychomotor vigilance tasks (PVT) to induce mental fatigue. The other session served as a control condition.
RESULTS: Older adults exhibited an ∼18% reduction in composite GS associated with mental effort, which was significantly greater than that observed in young adults. Indirect neural activation, assessed via the MFFD, was reduced by approximately 22% in older adults during mental effort, which was significantly greater than the reduction observed in young adults.
CONCLUSIONS: : These findings indicate that mental exertion/fatigue results in decreased composite GS and increasing impairments in neural activation in older adults. No effect on indices of neuromuscular performance were observed in young adults. These findings suggest that neural mechanisms are heavily involved in the regulation of composite grip strength, and that the relative contribution of neural and muscular mechanisms of handgrip strength are state dependent in older adults.