Effect of training with different intensities and volumes on muscle fibre enzyme activity and cross sectional area in the m. triceps brachii.

This study primarily examined how intermittent versus continuous endurance training, using similar or dissimilar volumes, affected muscle fibre enzyme activities in the triceps brachii muscle. Thirty-two subjects performed either intermittent (60% of 1RM) or continuous (30% of 1RM) elbow extensions 3 times week(-1) in a training apparatus. Training was performed until either a low (five) or a high volume (8 weeks) was accumulated. Muscle biopsies from the m. triceps brachii were taken pre- and post training and following 8 weeks of detraining. Marker enzymes for muscle fibre oxidative (succinate dehydrogenase SDH) and glycolytic (glycerophosphate dehydrogenase; alpha-GPDH) capacity was assessed by histochemistry, and the resulting enzyme activities measured by image analysis. The type of training affected enzyme activities differently. In type 1 fibres, continuous and intermittent training was equally effective in increasing SDH activity, while intermittent training increased SDH activity more than continuous training in type 2 fibres (P < 0.05). Intermittent training increased alpha-GPDH activity more than continuous training both in type 1 (P < 0.001) and type 2 fibres (P < 0.05), but the increase in glycolytic capacity following intermittent training was larger in type 1 (54%) than in type 2 fibres (23%). There was no effect of training volume on oxidative or glycolytic capacity in either fibre type. Thus, when training intensity is sufficient to stimulate to increases in oxidative and glycolytic capacity, the SDH and alpha-GPDH response seems to be volume independent. Detraining reduced Post-T enzyme activities to baseline (all; P < 0.01).