Short-term sprint interval versus traditional endurance training:: similar initial adaptations in human skeletal muscle and exercise performance

Brief, intense exercise training may induce metabolic and performance adaptations comparable to traditional endurance training. However, no study has directly compared these diverse training strategies in a standardized manner. We therefore examined changes in exercise capacity and molecular and cellular adaptations in skeletal muscle after low volume sprint-interval training (SIT) and high volume endurance training (ET). Sixteen active men (21 +/- 1 years, V-O2peak = 4.0 +/- 0.21 min(-1)) were assigned to a SIT or ET group (n = 8 each) and performed six training sessions over 14 days. Each session consisted of either four to six repeats of 30s 'all out' cycling at similar to 250%. V-O2peak with 4 min recovery (SIT) or 90-120 min continuous cycling at similar to 65%. V-O2peak (ET). Training time commitment over 2 weeks was similar to 2.5 h for SIT and similar to 10.5 h for ET, and total training volume was similar to 90% lower for SIT versus ET (similar to 630 versus similar to 6500 kJ). Training decreased the time required to complete 50 and 750 kJ cycling time trials, with no difference between groups (main effects, P <= 0.05). Biopsy samples obtained before and after training revealed similar increases in muscle oxidative capacity, as reflected by the maximal activity of cytochrome c oxidase (COX) and COX subunits II and IV protein content (main effects, P = 0.05), but COX II and IV mRNAs were unchanged. Training-induced increases in muscle buffering capacity and glycogen content were also similar between groups (main effects, P = 0.05). Given the large difference in training volume, these data demonstrate that SIT is a time-efficient strategy to induce rapid adaptations in skeletal muscle and exercise performance that are comparable to ET in young active men.