Skeletal muscle metabolism and ultrastructure in relation to age in sedentary men

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Abstract
To find out if there are age-related changes in human skeletal muscle metabolism or ultrastructure, biopsy material from 56 sedentary men aged 22-65 yr was studied by enzyme activity determinations, histochemistry and quantitative EM. For comparison, a younger (16-18 yr) and an older (66-76 yr) group were included. These subjects were relatively more active. There was an increase in percentage of slow twitch fibers with age. Mitochondrial volume fraction decreased with age, primarily due to diminished mean mitochondrial volume. In spite of this, no overall decrease in the activities of 5 enzymes, representative of the major pathways in energy metabolism, was observed. Increased amounts of enzymes/unit mitochondrial volume are implicated. Lipofuscin was more frequently found in the older groups. Correlations were present between fiber type distribution and oxidative enzymes, and between different enzymes. The decrease in maximal O2 uptake and muscular strength in aging humans probably may not be explained in terms of a deteriorating skeletal muscle energy metabolism.