Maximum activities of key glycolytic and oxidative enzymes in human muscle from differently trained individuals.

1. The maximum activities of hexokinase, 6-phosphofructokinase and oxoglutarate dehydrogenase, together with capillary density and fibre composition, have been measured in muscle from male and female untrained, medium-trained and well trained individuals. 2. The activity of hexokinase was almost identical in muscle from the three groups, whereas that of 6-phosphofructokinase decreased and that of oxoglutarate dehydrogenase increased with increased training. Values of maximum rate of O2 uptake (VO2, max) were also measured and were 21% higher in medium-trained and 49% higher in well trained compared to untrained individuals, whereas oxoglutarate dehydrogenase activities were 39% and 90% higher respectively. 3. There was a good positive correlation between the activity of oxoglutarate dehydrogenase and the percentage of type I fibres but the correlation between VO2, max and oxoglutarate dehydrogenase activity was less good. Changes in the values of VO2, max represent the effects on the circulatory and respiratory system whereas those in oxoglutarate dehydrogenase represent local effects of endurance training.