Energetic Cost of Maximal and Submaximal Voluntary Contractions in Young and Older Adults

Abstract

It has been shown recently that the ATP cost of a stimulated twitch contraction is lower in the skeletal muscle of older compared with young individuals, thus demonstrating a peripheral (muscular) bioenergetic adaptation in older muscle that is consistent with its slower contractile properties. However, it is not known whether these results extend to voluntary contractions, which involve both central (neural) and peripheral processes. Further, the effect of contraction intensity on age-related differences in cost is not known, despite the likelihood of variation between young and old in neural activation strategies during submaximal contractions. PURPOSE: To compare the ATP cost of voluntary contractions over a range of contraction intensities in the ankle dorsiflexor muscles of young and older men. METHODS: Six young (mean age: 20 years) and 6 older (mean age: 72) men performed 12-s isometric contractions of the dorsiflexors at 20%, 50% and 100% of maximal voluntary contraction (MVC) torque. Phosphorous magnetic resonance spectroscopy was used to quantify the ATP cost of contractions at each intensity. RESULTS: Maximal isometric torque was higher in young (57.1± 16.5 Nm, mean±SD) than older (41.9±8.0 Nm) men (p=0.07). The cost (mM ATP) of contraction is shown in Table 1 for young and older men at each relative contraction intensity. The cost of contraction increased with increasing torque for both young and older groups (p<0.01). Overall, older subjects had a lower cost of contraction than young (p=0.08), and there was no group-by-contraction intensity interaction (p=0.16). CONCLUSIONS: These results are consistent with previous findings of lower energetic cost of older muscle during twitch contractions. The current study extends these previous results to voluntary contractions, and suggests that the age-related difference in in vivo energetic cost and may be peripheral in nature and not affected by contraction intensity. Support: NIA R01 AG21094TABLE