Mitochondrial adaptations to high-volume exercise training are rapidly reversed after a reduction in training volume in human skeletal muscle

Increasedmitochondrial content andrespiration havebothbeenreported after exercise training.However, no study has directly compared how different training volumes influencemitochondrial respiration andmarkers of mitochondrial biogenesis. Ten healthy men performed high-intensity interval cycling during 3 consecutive training phases; 4wk of normal-volume training (NVT; 3/wk), followed by 20 d of high-volume training (HVT; 2/d) and 2 wk of reduced-volume training (RVT;5 sessions).Resting biopsy samples (vastus lateralis) were obtained at baseline and after each phase. Nomitochondrial parameter changed after NVT. After HVT,mitochondrial respiration and citrate synthase activity(~40-50%), aswell as theprotein content of electrontransport system (ETS) subunits (~10-40%), and that of peroxisome proliferator-activated receptor γ coactivator-1a (PGC-1α), NRF1, mitochondrial transcription factor A (TFAM), PHF20, and p53 (~65-170%) all increased compared to baseline;mitochondrial specific respiration remained unchanged. After RVT, all themitochondrial parametersmeasured except citrate synthase activity (~36% above initial) were not significantly different compared to baseline (all P > 0.05). Our findings demonstrate that training volume is an important determinant of training-induced mitochondrial adaptations and highlight the rapid reversibility of human skeletalmuscle to a reduction in training volume.¡Granata, C., Oliveira, R. S. F., Little, J. P., Renner, K., Bishop, D. J. Mitochondrial adaptations to high-volume exercise training are rapidly reversed after a reduction in training volume in human skeletal muscle.