Optimizing interval training through power output variation within the work intervals

Maximal oxygen uptake (V̇O2max) is a key determinant of endurance performance. Therefore, devising high-intensity interval training (HIIT) that maximizes stress of the oxygen transport and utilization systems may be important to stimulate further adaptation in athletes. We compared physiological and perceptual responses elicited by work intervals matched for duration and mean power output, but differing in power output distribution. Methods. Fourteen cyclists (V̇O2max: 69.2 ± 6.6 ml·kg-1·min-1) completed three laboratory visits for a performance assessment and two HIIT sessions using either varied- or constant-intensity work intervals. Results. Cyclists spent longer time at >90%V̇O2max during HIIT with varied-intensity work intervals (410 ± 207 vs. 286 ± 162 s; P = 0.02), but there were no differences between sessions in heart rate- or perceptual-based training load metrics (all P ≥ 0.1). When considering individual work intervals, minute ventilation (V̇E) was higher in the varied-intensity mode (F = 8.42; P = 0.01), but not respiratory frequency, tidal volume, blood lactate concentration [La], ratings of perceived exertion, or cadence (all F ≤ 3.50; P ≥ 0.08). Absolute changes (Δ) between HIIT sessions were calculated per work interval, and Δ total oxygen uptake was moderately associated with ΔV̇E (r = 0.36; P = 0.002). Conclusions. In comparison to a HIIT session with constant-intensity work intervals, well-trained cyclists sustain higher fractions of V̇O2max when work intervals involve power output variations. This effect is partially mediated by an increased oxygen cost of hyperpnoea, and not associated with a higher [La], perceived exertion or training load metrics.