The effect of continuous and interval exercise on PGC-1a and PDK4 mRNA in type I and type II fibres of human skeletal muscle

Aim: Differences in fibre-type recruitment during exercise may induce a heterogenic response in fibre-type gene expression. We have investigated the effect of two different exercise protocols on the fibre-type-specific expression of master genes involved in oxidative metabolism [proliferator-activated receptor-? coactivator-1a (PGC-1a) and Pyruvate dehydrogenase kinase 4 (PDK4)]. Methods: Untrained subjects (n = 7) completed 90- min cycling either at a constant intensity [continuous exercise (CE): approximately 60% of _ V O2max] or as interval exercise (IE: approximately 120/ 20% _ V O2max, duty cycle 12/ 18s). Muscle samples were taken before (pre) and 3 h after (post) exercise. Single fibres were isolated from freeze- dried muscle and characterized as type I or type II. The cDNA from two fibres of the same type was pooled and mRNA analysed with reverse transcription quantitative real- time PCR. Results: Continuous exercise and IE elicited a small increase in blood lactate (< 2.5 mm) and moderate glycogen depletion (< 40%) without difference between exercise modes. The mRNA of PGC- 1a and PDK4 increased 5- to 8fold in both fibre types after exercise, and the relative increase was negatively correlated with the basal level. However, the mRNA of PGC- 1a and PDK4 was not different between type I and II fibres neither pre nor post, and there was no difference in the exercise- induced response between fibre types or exercise modes. Conclusion: We conclude that the mRNA of PGC- 1a and PDK4 increases markedly in both fibre types after prolonged exercise without difference between CE and IE. The similar response between fibre types may relate to that subjects were sedentary and that the metabolic stress was low.