COMPENSATORY MUSCLE-FIBER HYPERTROPHY IN ELDERLY MEN

Muscle strength and muscle morphology have been studied three times during a period of 11 yr in nine elderly men. On the last occasion the average age was 80.4 (range 79-82) yr. Body cell mass decreased by 6% and muscle strength for knee extension, measured by means of isometric and concentric isokinetic (30-60-degrees/s) recordings, declined by 25-35% over the 11-yr period. Between 76 and 80 yr of age only the isokinetic strength for 30-degrees/s decreased significantly. Muscle fiber composition in the vastus lateralis did not change between 69 and 76 yr of age, but there was a significant reduction in the proportion of type IIb fibers from 76 to 80 yr. The decrease in type II fiber areas was not significant between 69 and 76 yr of age (as in a larger sample from the same population), but a significant increase in both type I and type Il fiber areas was recorded from 76 to 80 yr of age and biceps brachii showed similar tendencies. In the same period, the enzymatic activities of myokinase and lactate dehydrogenase subsided in the vastus lateralis, but there was no change for triose phosphate dehydrogenase, 3-hydroxy-CoA-dehydrogenase, and citrate synthase. The muscle fiber hypertrophy in this group of elderly men with maintained physical activity between 76 and 80 yr of age is interpreted as a compensatory adaptation for the loss of motor units. In addition, the adaptation with respect to oxidative capacities seems to be maintained at this age.