EFFECT OF AGING ON HUMAN ADDUCTOR POLLICIS MUSCLE FUNCTION

The effect of aging on the voluntary and electrically evoked contractile properties of the human adductor pollicis muscle was investigated in 70 healthy male subjects aged 20-91 yr, 10 subjects for each decade. Maximum isometric voluntary force declined significantly (range of P values < 0.001-0.05) after the age of 59 yr, dropping by the eighth decade to 57.6% of the level recorded in the second decade. A significantly shift (P range < 0.001-0.05) to the left of the frequency-force curve after ulnar nerve supramaximal stimulation at 1, 10, 20, 30, and 50 Hz was observed in the most elderly group (> 80 yr) compared with the youngest group (20-29 yr). Maximum relaxation rate dropped by 48.7% from the second to the eighth decade. The decrease became significant (P range < 0.05-0.001) with the sixth decade. Isometric endurance, evaluated during 30 s of stimulation at 30 Hz, showed a linear (P < 0.001) increase with age. Aged muscle is thus weaker, slower, and tetanized at lower fusion frequencies but, paradoxically, more resistant to static fatigue.