|Clark, David J.|
|Fielding, Roger A.|
Submitted to: European Journal of Applied Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/29/2011
Publication Date: 10/18/2011
Citation: Reid, K., Doros, G., Clark, D., Patten, C., Carabello, R., Cloutier, G., Phillips, E., Krivickas, L., Frontera, W., Fielding, R. 2011. Muscle power failure in mobility-limited adults: preserved single muscle fibre function despite reduced whole muscle size, quality and neuromuscular activiation. European Journal of Applied Physiology. 112(6):2289-2301. PMID:22005960. Interpretive Summary: Lower body muscle power is important for maintaining functional independence and mobility amoung older adults. Greater knowledge of the major factors that are associated with the decline in muscle power among older adults is necessary and could provide important information for intervention and management strategies targeting mobility loss among older persons. This study examined the physiological determinants of muscle power among three distinct populations: healthy middle aged, healthy older and mobility limited older males and females. Our analysis of muscle biopsy samples in mobility-limited elders also revealed that surviving muscle fibers had enlarged and compensated for the age-related losses in whole muscle power and mobility with advancing age may be caused, particular, by impairments in neuromuscular activation and a concomitant reduction in muscle quality.
Technical Abstract: This study investigated the physiological and gender determinants of the age-related loss of muscle power in 31 healthy middle-aged adults (aged 40-55 years), 28 healthy older adults (70-85 years) and 34 mobility-limited older adults (70-85 years). We hypothesized that leg extensor muscle power would be significantly lower in mobility-limited elders relative to both healthy groups and sought to characterize the physiological mechanisms associated with the reduction of muscle power with aging. Computed tomography was utilized to assess mid-thigh body composition and calculate specific muscle power and strength. Surface electromyography was used to assess rate of neuromuscular activation and muscle biopsies were taken to evaluate single muscle fiber contractile properties. Peak muscle power, strength, muscle cross-sectional area, specific muscle power and rate of neuromuscular activation were significantly lower among mobility-limited elders compared to both healthy groups (P = 0.05). Mobility-limited older participants had greater deposits of intermuscular adipose tissue (P < 0.001). Single fiber contractile properties of type I and type IIA muscle fibers were preserved in mobility-limited elders relative to both healthy groups. Male gender was associated with greater decrements in peak and specific muscle power among mobility-limited participants. Impairments in the rate of neuromuscular activation and concomitant reductions in muscle quality are important physiological mechanisms contributing to muscle power deficits and mobility limitations. The dissociation between age-related changes at the whole muscle and single fiber level suggest that, even among older adults with overt mobility problems, contractile properties of surviving muscle fibers are preserved in an attempt to maintain overall muscle function.