Extremely low-volume, high-intensity interval training improves exercise capacity and increases mitochondrial protein content in human skeletal muscle

Purpose: The purpose of the present study was to evaluate whole-muscle content of several proteins involved in the regulation of skeletal muscle mitochondrial protein content and anaerobic capacity following 4 weeks of extremely low-volume high-intensity interval training (HIT). Methods: Young, healthy, recreationally active adult males (n = 8) trained 4 times a week for 4 weeks on a cycle ergometer. Each session involved 4 min of total exercise comprised of eight 20 s intervals at ~170% of peak aerobic power separated by 10 s rest. Muscle biopsies were taken prior to (pre) and ~72 hrs post-training (post). Participants completed an incremental peak oxygen uptake (VO2peak) test and a Wingate test pre-, mid-, and post-training. Results: VO2peak was elevated (p < 0.05) at mid- (p < 0.05) and post-training (pre: 40.5 ± 3.8 ml·kg −1 ·min −1 , mid: 43.4 ± 2.5 ml·kg −1 ·min −1 , post-: 47.2 ± 2.9 ml·kg −1 ·min −1 ). Wingate mean power also increased with training (pre-: 701.0 ± 73.0 W, mid-: 745.5 ± 73.3 W, post-: 786.8 ± 80.0 W). While maximal citrate synthase activity was unchanged, protein expression of the mitochondrial protein cytochrome c oxidase (COX) subunit I (+27%; p < 0.05) and COX IV (+26%; p < 0.05), PDK2 (+28%; p = 0.08) increased. Increases (p < 0.05) in both total PGC-1α (+19%), and nuclear PGC-1α (+46%) were also observed after 4 weeks of HIT. No changes were observed in the whole-muscle contents of PDHe1a, PDK4, SIRT1, mTOR, S6K1, MCT1, or PFK protein. Conclusions: These results demonstrate that several mitochondrial protein (but not citrate synthase activity), PGC-1α protein content, and exercise capacity can be improved in only 4 min of total training time per day, 4 days per wk using HIT cycle training.