Effects of high- and moderate-intensity training on metabolism and repeated sprints.

PURPOSE We compared the effects of high-intensity interval (HIT) and moderate-intensity continuous (MIT) training (matched for total work) on changes in repeated-sprint ability (RSA) and muscle metabolism. METHODS Pre- and posttraining, VO(2peak), lactate threshold (LT), and RSA (5 x 6-s sprints, every 30 s) were assessed in 20 females. Before and immediately after the RSA test, muscle biopsies were taken from the vastus lateralis. Subjects were matched on RSA, randomly placed into the HIT (N = 10) or MIT (N = 10) group and performed 5 wk (3 d.wk(-1)) of cycle training; performing either HIT (6-10, 2-min intervals at 120-140% LT) or MIT (continuous, 20-30 min at 80-95% LT). RESULTS Both groups had significant improvements in VO(2peak) (10-12%; P < 0.05) and LT (8-10%; P < 0.05), with no significant differences between them. Both groups also had significant increases in RSA total work (kJ) (P < 0.05), with a significantly greater increase following HIT than MIT (13 vs 8.5%, respectively; P < 0.05). There was a significant decrease in resting [ATP] and an increase in postexercise [La(-)](b) for both groups, but no significant differences between them. There were no significant changes in resting or postexercise [PCr], [Cr], muscle [La(-)], or [H(+)] after the training period. CONCLUSIONS When total work is matched, HIT results in greater improvements in RSA than MIT. This results from an improved ability to maintain performance during consecutive sprints, which is not explained by differences in work done during the first sprint, aerobic fitness or metabolite accumulation at the end of the sprints.