Low mean level sustained and intermittent grip exertions: Influence of age on fatigue and recovery

Abstract

The goal of this study was to quantify localised muscle fatigue resulting from low mean levels of exertion in younger (< 40 years) and older (>50 years) adults. Fatigue, elicited in the finger flexor muscles by intermittent (10% mean maximum voluntary contraction (MVC)) and sustained (8% MVC) handgrip exercises, was quantified by a muscle twitch force response before, immediately after and during 3 h following exercise. Despite greater mean loads, recovery time was shorter following intermittent than sustained contractions, which suggests that recovery from fatigue is more sensitive to rest within the work cycle than mean work. The more pronounced effects for younger than older individuals following the sustained exertion indicate that changes in muscle fibre type composition might predispose older individuals to be more resistant to fatigue resulting from sustained contractions of low level. Performing hand exertion tasks requiring low mean force levels contributes to similar long-lasting fatigue effects regardless of gender and age. Intermittent periods of complete rest reduce muscle fatigue. Since fatigue was not perceived during recovery from the tested sustained and intermittent contractions, subjective evaluations may not be a reliable indicator of localised muscle fatigue.

Keywords:

• fatigue of long duration
• muscle work cycle
• ageing
• hand grip exertion

Acknowledgements

Support for this research was provided by the National Institute on Disability and Rehabilitation Research of the United States Department of Education, Grant no. H133E980007, ‘Rehabilitation Engineering Research Center’ at the University of Michigan and research funding by the Occupational Therapy Department at Wayne State University. The opinions contained in this publication are those of the grantee and do not necessarily reflect those of the United States Department of Education. The authors thank James Foulke and Eyvind Claxton for the design of the instrumentation and their control interfaces.