Hypoxia compromises training quality, yet high-intensity interval training (HIIT) performed under hypoxia may elicit greater benefits than does normoxic HIIT. However, its effects on pacing and perceived exertion remain underexplored, particularly in moderate-altitude distance runners. This study aimed to compare the efficacy of HIIT performed at low (∼1,220 m) versus moderate (∼2,850 m) altitudes on pacing and rated perceived exertion (RPE) during a 5,000 m race. Forty-two moderate-altitude inhabitant runners (men/women, 23/19) were randomly allocated into the HIIT groups at ∼2,850 m (HIIT2850m, n=14) and at ∼1,220 m (HIIT1220m, n=14), and the control group at ∼2,850 m (CG2850m, n=14). The HIIT intervention was completed by the HIIT2850m group at moderate altitude and the HIIT1220m group, which travelled to low altitude for 8 weeks with 2 sessions.wk -1 . Each session consisted of 4x4 min intervals at 100% velocity at maximum oxygen consumption (vVO 2 max, determined at their respective training sites), with 3 min recovery at 70% vVO 2 max intensity. Before and after the intervention, 5,000 m races were performed in a matched group on a 400 m track at ∼2,850 m and every km speed and RPE were recorded. The results indicated that the participants used a similar parabolic reversed-J shaped strategy, with significant 5,000-m time improvements observed in both the HIIT1220m (Δ:-20.1±23.7 s, p = 0.001) and the HIIT2850m (Δ:-16.7±25.9 s, p=0.001) groups. A significant main effect of time (except at the 2 nd km, p = 0.693) and a main effect of group (at the 1 st km, p = 0.034 and 5 th km, p = 0.044) were observed in pace, along with a significant group-by-time interaction in all km segments. Compared with the CG2850m, both interventions demonstrated significantly greater speeds at the 1 st and 5 th km and lower RPE, with greater changes in the HIIT1220m group. The results suggest that HIIT at both altitudes improved performance and RPE, with quality training at low altitudes producing greater benefits, offering strategic insights for athletes and coaches. • An 8-week high-intensity interval training (HIIT), conducted at either low or moderate altitude, improved 5,000 m performance, pacing speed, and reduced perceived exertion. • The observed reductions in perceived exertion reflect improved tolerance to running intensity and more effective pacing regulation, which collectively contributed to faster performance outcomes. • HIIT performed at low altitude elicited comparatively greater benefits in pacing and perceptual responses than did the same training conducted at moderate altitude.
Fentaw et al. (Sun,) studied this question.