Morphology and enzymatic capacity in arm and leg muscles in 78–81 year old men and women

Abstract

Twelve men and twelve women 78-81 years of age were studied with muscle biopsies from the right vastus lateralis and biceps brachii and with measurements of isometric and isokinetic strength for knee-extension and isometric strength for elbow-flexion. Bicycle ergometry with determination of heart rate and O2 uptake at submaximal (50 W) and maximal work loads was also performed. Body cell mass was estimated from measurements of total body K. Muscle fiber composition with respect to slow twitch (ST = type I) and fast twitch (FT = type II) fibers did not differ between the sexes and the younger subjects drawn from population studies. The mean fiber areas in vastus lateralis averaged, 4.7 and 3.3 .times. 103 .mu.m2 in men and women, respectively. This is from less than 10 up to 30% of the values found in sedentary younger subjects. The decline dominated in FT fibers, especially FTb fibers. In contrast, biceps brachii did not show any matched fiber size reduction. The number of atrophic fibers was high and so was the frequency of enclosed fibers and areas with type grouping (ST fibers), indicating denervation-reinnervation. Such abnormalities are rarely seen at younger ages. Correlation analysis showed that only a minor part of the reduction in body cell mass with age could be explained by a reduction in fiber areas and that a reduction with age of the number of muscle fibers of both fiber types must be assumed. Positive correlations were observed between muscle strength and mean fiber and FT areas. Comparing the present findings of skeletal muscle morphology with those in younger age groups, it is apparent that during the 8th decade of life major changes do occur. The measurements of aerobic and anaerobic enzymatic activities and of muscle capillary supply showed that levels comparable to those of younger age groups are maintained. Thus, quantitative rather than qualitative changes may explain the reduction in work performance with age.