Abstract
High intensity interval training (HIIT) involves repeated bouts of relatively hard work, commonly at intensities eliciting ≥ 80% of maximal heart rate (HR(max)), interspersed with recovery periods. Anchoring intensity to HR(max) can elicit a wide range of acute metabolic responses to exercise. Expressing intensity relative to metabolic thresholds such as critical power (CP) may reduce this variability. We therefore examined whether anchoring HIIT to CP reduced variability in change in [blood lactate] (ΔBLa(−)) compared to HR(max)-based approach. Nineteen adults aged 23 ± 4 years completed two 4 × 4-min HIIT trials in a randomized, crossover manner at intensities equal to CP + 10% of work prime (CP(HIIT)) or ≥ 80% HR(max) (HR(HIIT)). Variability in [ΔBLa(−)] from rest to exercise was not different between CP(HIIT) and HR(HIIT) (1.37 (0.42–1.62) vs. 1.32 (0.77–1.97) mM; p = 0.75). Workload was higher in CP(HIIT) vs. HR(HIIT) (192 ± 39 W vs. 180 ± 43 W; p = 0.001), as was exercise oxygen consumption, ventilation, respiratory exchange ratio, heart rate, and rating of perceived exertion (all p < 0.05). A CP-based HIIT protocol did not reduce variability of change in [ΔBLa(−)] compared to a traditional approach anchored to %HR(max). However, anchoring HIIT intensity to CP resulted in participants achieving higher workloads, eliciting higher cardiorespiratory and perceived stress which could translate to divergent training-induced responses. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1038/s41598-025-28231-y.