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Title: Impaired neural activation limits muscle power in mobility-limited older adults

Author
item CLARK, DAVID - Department Of Veterans Affairs
item PATTEN, CAROLYNN - Department Of Veterans Affairs
item REID, KIERAN - Jean Mayer Human Nutrition Research Center On Aging At Tufts University
item CARABELLO, ROBERT - Jean Mayer Human Nutrition Research Center On Aging At Tufts University
item PHILLIPS, EDWARD - Harvard Medical School
item Fielding, Roger

Submitted to: Journal of Gerontology Biological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2009
Publication Date: 5/20/2010
Citation: Clark, D.J., Patten, C., Reid, K.F., Carabello, R.J., Phillips, E.M., Fielding, R. 2010. Impaired neural activation limits muscle power in mobility-limited older adults. Journal of Gerontology Biological Science. 65(5):495-502.

Interpretive Summary: Older adults often have difficulty walking and performing other mobility-related tasks. Previous research has shown that muscle power (strength during movement) may be an important factor limiting mobility performance with aging. Therefore, it is important to understand how muscle power is produced and how to prevent loss of muscle power. This study examines whether the nervous system may be responsible for declines in muscle power and mobility with aging. We tested healthy middle-aged adults, healthy older adults and older adult with poor mobility. We found that the older adults with poor mobility also had the lowest muscle power and the lowest levels of neural activation of muscle. These problems were most severe at the fastest movement speeds. These findings suggest that not all older adults have neural deficits, but in those that do it may be a serious factor leading to mobility problems.

Technical Abstract: Declines in functional mobility are common with advancing age, though the physiological determinants underlying this problem are not fully understood. Accumulating evidence indicates that muscle power, the product of force and velocity, is an independent predictor of mobility function in older adults. Accordingly, assessment of high velocity dynamic neuromotor performance may provide insight to specific age-related impairments responsible for deficits in mobility function. To elucidate age-related neuromuscular contributions to mobility deficits, we studied maximal voluntary dynamic muscle performance in three distinct cohorts: middle-aged healthy adults, older healthy adults and older adults with mobility limitations. Marked velocity-dependent impairment of agonist muscle activation was revealed in the older mobility-limited group relative to the middle-aged and older healthy groups. Torque and power were also more compromised in the older mobility-limited group, with the greatest deficits occurring at the fastest movement velocities. These findings suggest that neuromotor impairments are not an obligatory consequence of aging. Rather, they may be a primary contributor to functional mobility deficits in a subset of the aging population.