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, VO_2peak 52 ± 6 mL kg/min) were randomized to four training groups with equivalent training the previous 2 months (～6 h/wk, ～1.5 int. session/wk). Low only (n=8) trained 4–6 sessions/wk at a low‐intensity. Three groups (n=9 each) trained 2 sessions/wk × 7 wk: 4 × 4 min, 4 × 8 min, or 4 × 16 min, plus 2–3 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 HR_peak and 4.9, 9.6, and 13.2 mmol/L blood lactate in 4 × 16, 4 × 8, and 4 × 4 min groups, respectively (both P<0.001). 4 × 8min training induced greater overall gains in VO₂peak, power@VO₂peak, and power@4 mM bLa‐ (Mean ± 95%CI): 11.4 (8.0–14.9), vs 4.2 (0.4–8.0), 5.6 (2.1–9.1), and 5.5% (2.0–9.0) in Low, 4 × 16, and 4 × 4 min groups, respectively (P<0.02 for 4 × 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.