Quantitative measures of enzyme activities in type I and type II muscle fibres of man after training.

The effect of 7 to 8 weeks of physical training on oxidative and glycolytic enzyme activities in the 2 major fibre types of human quadriceps femoris muscle has been investigated. 2 groups of 4 and 5 subjects respectively were trained at the same total work-load on a bicycle ergometer 3 days per week using interval exercise with maximal intensity (I.T.) or continuous exercise with submaximal intensity (C.T.). Succcinate dehydrogenase (SDH) and phosphofructokinase (PFK) activities were determined on crude homogenates of muscle biopsy samples and on pools of type I and type II fibres dissected from freeze-dried samples taken before and after training. Crude homogenate SDH activity increased to the same extent in both groups, average increases were 27.5% (I.T.) and 22% (C.T.) respectively. Only type I-SDH increased in the C.T. group (p less than 0.01), the average increase being 32%. On the other hand only type II-SDH increased in the I.T. group (p less than 0.01), with an average increase of 49%. No changes in PFK activity could be detected. The results of the present study emphasize the great adaptability in oxidative potential of both the two major human skeletal muscle fibre types and further that this adaptation seems to be related to the pattern of fibre recruitment during exercise.