Adaptations to aerobic interval training: interactive effects of exercise intensity and total work duration

To compare the effects of three 7-week interval training programs varying in work period duration but matched for effort in trained recreational cyclists. Thirty-five cyclists (29 male, 6 female, VO2peak 52 +/- 6 mL kg/min) were randomized to four training groups with equivalent training the previous 2 months (similar to 6 h/wk, similar to 1.5 int. session/wk). Low only (n=8) trained 46 sessions/wk at a low-intensity. Three groups (n=9 each) trained 2 sessions/wk x 7 wk: 4 x 4 min, 4 x 8 min, or 4 x 16 min, plus 23 weekly low-intensity bouts. Interval sessions were prescribed at the maximal tolerable intensity. Interval training was performed at 88 +/- 2, 90 +/- 2, and 94 +/- 2% of HRpeak and 4.9, 9.6, and 13.2 mmol/L blood lactate in 4 x 16, 4 x 8, and 4 x 4 min groups, respectively (both P<0.001). 4 x 8min training induced greater overall gains in VO2peak, power@VO2peak, and power@4 mM bLa- (Mean +/- 95%CI): 11.4 (8.014.9), vs 4.2 (0.48.0), 5.6 (2.19.1), and 5.5% (2.09.0) in Low, 4 x 16, and 4 x 4 min groups, respectively (P<0.02 for 4 x 8 min vs all other groups). Interval training intensity and accumulated duration interact to influence the adaptive response. Accumulating 32 min of work at 90% HR max induces greater adaptive gains than accumulating 16 min of work at 95% HR max despite lower RPE.