Assessing Acute Responses to Exercises Performed Within and at the Upper Boundary of Severe Exercise Domain.

Purpose: The highest work-rate that provides maximal oxygen uptake ($\dot{V}{O}_{2max}$) may be one of the best exercise stimuli to yield both $\dot{V}{O_2}_{max}$ and lactate accumulation. The aim of this study was to analyze physiological and metabolic acute responses of an exercise modality performed at the upper boundary of the severe exercise domain, and compare those responses with exercise modalities applied within the severe exercise domain. Method: Ten trained male cyclists participated in this study. The $\dot{V}{O}_{2max}$, corresponding power output (PO_VO2max), and the highest work-rate that provides the $\dot{V}{O}_{2max}$ (I_HIGH) were determined by constant work-rate exercises. Cyclists performed three high-intensity interval training (HIIT) strategies as follows; HIIT-1: 4-6 × 3-min at 95% of PO_VO2max with 1:1 (workout/rest ratio); HIIT-2: 16-18 × 1-min at 105% of PO_VO2max with 1:1; HIIT-3: 4-7 × 1-2-min at the I_HIGH with 1:2. Capillary blood samples were analyzed before, immediately after HIIT sessions, and at the first, third, and fifth minutes of recovery periods. Lactate difference between the highest lactate response and resting status was considered as the peak lactate response for each HIIT modality. Results: Time spent at $\dot{V}{O}_{2max}$ was greater at HIIT-1 and HIIT-3 (272 ± 127 and 208 ± 111 seconds, respectively; p = 0.155; effect size = 0.43) when compared to the HIIT-2 (~26 seconds; p < 0.001), while there was a greater lactate accumulation at HIIT-3 (~16 mmol·L^-1) when compared to HIIT-1 and HIIT-2 (12 and 14 mmol·L^-1, respectively; p < 0.001). Conclusions: In conclusion, HIIT-3 performed at I_HIGH was successful to provide time spent at $\dot{V}{O}_{2max}$ with a greater lactate accumulation in a single session.