Aging and Human Neuromuscular Function

Abstract

<p>In view of the importance of maintaining normal mobility in the aging population, the function of two opposing groups of leg muscles, the ankle dorsiflexors and plantarflexors, was studied in a sample of 111 healthy men and women aged 20 to 100 yr. Three major questions were asked in this investigation: (1) To what extent does muscle strength decline with age? (2) Can descending motor pathways be optimally utilized by the elderly for activating lower motor neurons? (3) Does the time-course of muscle contraction become prolonged with age?</p> <p>Summarized results were:</p> <p>1. Maximal voluntary isometric strength (MVC) of the dorsiflexor and plantarflexor muscles showed a general pattern of decreased values after the fifth decade in both sexes. A similar decline of approximately 13% per decade was observed in the two muscle groups. As the plantarflexor muscles produced 4 times more torque than the dorsiflexor muscles in young adults, the absolute loss of strength was much greater for plantarflexor MVC.</p> <p>2. The majority of subjects at all ages were able to utilize their descending motor pathways optimally for full muscle activation.</p> <p>3. Contraction time and one-half relaxation time of the isometric twitch were prolonged with increased age in both muscles.</p> <p>4. An additional observation was that flexibility of the ankle joint was reduced with increased age, although considerable rotation of the ankle was still possible in the oldest subjects.</p> <p>Evidence from analysis of the compound muscle action potentials, peak twitch torques and muscle cross-sectional areas supported the conclusion that the decrease in strength with aging was due to a loss of excitable muscle mass. It was hypothesized that fat and connective tissue replaced muscle in the elderly. The findings of this study add to our knowledge about the aging process and its influence on neuromuscular function. It is also anticipated the results will be useful in geriatric clinics and for planning programs aimed at the prevention and rehabilitation of neuromuscular disability in the elderly population.</p>