Peripheral impairments cause a progressive age-related loss of strength and velocity-dependent power in the dorsiflexors.

ABSTRACT

Muscle power is more functionally relevant than static muscle strength, particularly with aging. However, the effect of age on power derived from isotonic contractions has been studied sparingly, and it has not been studied at all in subjects >75 yr of age. Thus the purpose was to investigate the magnitude and causes of age-related losses in isotonic power among 13 young (26 yr), 13 old (65 yr), and 13 very old (84 yr) men. Six different loads were employed to create velocity-torque and power-torque relationships. Dorsiflexor cross-sectional area was assessed via magnetic resonance imaging for the calculation of specific power. Electromyographic signals of the tibialis anterior and soleus muscles were recorded to assess agonist activation and antagonist coactivation, respectively. Despite similar contractile masses and levels of voluntary drive and antagonist co-activation, power was significantly impaired in the old vs. young (approximately 25%), and in the very old relative to both the young (approximately 60%) and old (approximately 40%). The novel results punctuate two important considerations for studies concerned with the effect of age on the neuromuscular system. First, the decreased ability of muscles from old men to produce power in the presence of reasonably well-preserved strength indicates the utility of studying isotonic contractions. Second, the precipitous decline in many measures between the seventh and ninth decades underscores the benefit of testing more than one group of aged subjects to improve our understanding of rates of change in key variables.