Enzyme Activities and Morphometry in Skeletal Muscle of Middle-Aged Men after Training

Abstract

The effect of 10–13 weeks of endurance training on the skeletal muscle of 10 previously sedentary 46–62-year old men has been studied. The training increased the initial maximal oxygen uptake (VO₂ max) of 2.6 l/min by 8%. Comparisons are also made with 9 still active runners aged 43–66 years. whose VO₂ max was 3.7 l/min. Muscle samples were taken from the thigh. Triosephosphate dehydrogenase (TPD), lactic dehydrogenase (LDH), and cytochrome oxidase (cytox) activities were measured, and the volume fractions of mitochondria, sarcoplasmic and fibrillar space, and fat droplets were estimated by morphometric methods from electron micrographs. Training produced only minor changes in the mitochondrial volume, simultaneously with an 80% increase in the cytox activity. The middle-aged runners had a larger mitochondrial volume and a cytox activity twice as high as the sedentary men before training. TPD activity was unaffected by training, whereas LDH activity was slightly enhanced by training, but the runners had only 40% of the sedentary men's activity. No other changes were observed in the ultrastructure of the muscles. The absence of significant response in mitochondrial volume and the moderate increase of VO₂ max during training distinguish middle-aged men from young men and may be interpreted as a negative effect of age on the ability of muscle to increase its work capacity.