Physiological Responses to High-Intensity Interval Exercise in Hypoxia Among Lean Males and Those With Overweight or Obesity

Abstract

This study aimed to compare physiological responses to high-intensity interval exercise (HIIE) in hypoxia and normoxia across different body mass index (BMI) categories. Twenty-one males, classified as normal-weight (NW, n = 9 and BMI: 22.9 ± 2.3 kg · m^-2) or overweight/obese (OW, n = 12 and BMI: 27.6 ± 2.0 kg · m^-2), completed graded exercise tests (GXT) in normoxia (FiO₂ = 20.9%) and hypoxia (FiO₂ = 14.0%), followed by three randomised HIIE sessions: hypoxia (HY), normoxia matched to hypoxic relative intensity (NR) and normoxia matched to hypoxic absolute intensity (NA). Blood samples were collected at baseline, immediately post-HIIE and at 3 and 24 h post-exercise. Both NW and OW groups had significant reductions in peak heart rate and peak power output in hypoxic versus normoxic GXT (p < 0.05). The NW group showed a greater decline in peak oxygen uptake $\left(\dot{V}{O}_2\text{peak}\right)$ under hypoxia compared to OW (Δ = 9.88 ± 5.0 vs. 5.22 ± 3.3 mL · kg · min^-1; p < 0.001). OW exhibited increased blood glucose levels post-hypoxic GXT compared to normoxic conditions (Δ = 0.358 mmol · L^-1; p = 0.025). During HIIE sessions, both groups showed similar heart rate, oxygen consumption, carbon dioxide production and respiratory exchange ratio responses. However, blood lactate concentration immediately after normoxic HIIE (NR) was higher in NW compared to OW (p < 0.05). Fasting blood glucose significantly increased immediately after normoxic HIIE in NW and immediately after hypoxic HIIE in OW (p < 0.05). HIIE in normoxia and hypoxia elicits similar physiological responses across BMI categories, though normal-weight individuals have greater reductions in $\dot{V}{O}_2\text{peak}$ and higher lactate responses during normoxic HIIE (NR), whereas overweight/obese individuals exhibit higher glucose increases post-hypoxic exercise, indicating potential BMI-specific metabolic benefits. These findings suggest that BMI could influence physiological adaptations in response to high-intensity exercise in hypoxia, suggesting that this form of exercise could be a beneficial alternative for improving metabolic health, especially in individuals with overweight or obesity.

Keywords: blood glucose; body mass index; cardiorespiratory fitness; exercise; simulated altitude.

FIGURE 1

Study design. B, baseline; GXT, graded exercise test; GXT‐H, GXT in hypoxia; GXT‐N, GXT in normoxia; HIIE, high‐intensity interval exercise; HY, hypoxia; NA, normoxia matched for absolute intensity with hypoxia; NR, normoxia matched for relative intensity with hypoxia; P0, immediately post‐exercise; P24, 24 h post‐exercise; P3, 3 h post‐exercise. *Venous blood collection.

FIGURE 2

Physiological responses to GXTs in normoxia and hypoxia among adults with normal‐weight (NW) and those with overweight or obesity (OW). Symbols connected by lines represent individual participants, with solid grey circles denoting the normoxia condition and coloured diamonds denoting the hypoxia condition. *p < 0.05. η _p ², partial eta squared; (A) PPO, peak power output; (B) LT, lactate threshold; (C) HR_peak, peak heart rate; (E) $\dot{\mathrm{V}}{\text{CO}}_2\text{peak}$, volume of peak carbon dioxide production; (D, F) $\dot{\mathrm{V}}{\mathrm{O}}_2\text{peak}$, peak oxygen uptake. (G) RER, respiratory exchange ratio. (H) Blood glucose level. (I) Blood lacate level.

FIGURE 3

Blood lactate (A) and glucose concentrations (B) and their relationship (C) following high‐intensity interval exercise under normoxic and hypoxic conditions among adults with normal‐weight (NW) and those with overweight or obesity (OW). Values are presented as means ± SD. 0 h Post, immediately after exercise; 3 h Post, 3 h post‐exercise; 24 h Post, 24 h post‐exercise; HY, hypoxia; NA, normoxia matched for absolute intensity with hypoxia; NR, normoxia matched for relative intensity with hypoxia; Pre, baseline. *p < 0.05. +represents a significant difference compared to pre within the same condition. #shows the significant difference compared to the OW group at the same time point within the same condition.

FIGURE 4

Area under the curve (AUC) values for blood lactate (A) and glucose concentrations (B) following HIIE under normoxic and hypoxic conditions among adults with normal‐weight (NW) and those with overweight or obesity (OW). Values are presented as means ± SD. HY, hypoxia; NA, normoxia matched for absolute intensity with hypoxia; NR, normoxia matched for relative intensity with hypoxia. *p < 0.05.