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

In order 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 years was studied by means of enzyme activity determinations, histochemistry and quantitative electron microscopy. For comparison, a younger (16-18 years) and an older (66-76 years) group were included. These subjects were relatively more active. There was an increase in percentage of slow twitch fibres 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 five enzymes, representative of the major pathways in energy metabolism, was observed. Thus, increased amounts of enzymes per unit mitochondrial volume are implicated. Lipofuscin was more frequently found in the older groups. Correlations were present between fibre type distribution and oxidative enzymes, as well as between different enzymes. It was concluded, that the decrease in maximal oxygen uptake and muscular strength in aging humans probably may not be explained in terms of a deteriorating skeletal muscle energy metabolism.