Purpose Respiratory frequency (fR) and tidal volume (VT) show distinct responses during high-intensity interval training (HIIT) bouts, yet the underlying mechanisms remain unclear. We investigated the effects of hypoxia and hyperthermia on ventilatory responses to HIIT bouts. Methods Ten recreationally trained males (mean ± SD: peak oxygen uptake: 3.98 ± 0.62 L/min, age: 28 ± 6 years) performed the same HIIT protocol to exhaustion in three randomized conditions: normobaric hypoxia (HYP, 15% O2), hyperthermia (HOT, 35 °C, 40% humidity), and control (CON, 18 °C and 40% humidity). Work–recovery phases (30–30 s) were performed at 109% of peak power output from a prior incremental test and 50 W, respectively. Results Time-to-exhaustion (TTE) differed (P < 0.05) across CON (18.0 ± 4.4 min), HYP (9.4 ± 2.8 min), and HOT (12.6 ± 3.1 min) conditions. Iso-time fR was associated with changes in TTE and positively correlated with perceived exertion (P < 0.001; r = 0.85) and aural temperature (P < 0.001; r = 0.58). On average, fR increased during the work phase and decreased during recovery, primarily driving pulmonary ventilation (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\dot{\text{V}}}_{{\text{E}}}\)</EquationSource> </InlineEquation>) during work–recovery alternations. Conversely, VT showed a smaller and opposite response, with higher values during recovery. VT plateaued in all conditions, but higher values were observed in HYP versus CON and HOT, accompanied by higher capillary blood lactate levels and lower blood oxygen saturation. Conclusions fR is associated with changes in exercise tolerance irrespective of the environmental conditions tested and is more closely related to perceived exertion than to aural temperature. fR primarily drives the <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\({\dot{\text{V}}}_{{\text{E}}}\)</EquationSource> </InlineEquation> response to high-intensity work–recovery alternations, while VT appears fine-tuned on fR levels and the magnitude of metabolic inputs.

Effects of normobaric hypoxia and hyperthermia on ventilatory responses to high-intensity interval training bouts

期刊论文
发表日期：

2026年7月2日

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Michele Girardi,
Andrea Nicolò,
Samuele M. Marcora,
Ilenia Bazzucchi,
Francesco Felici,
John Dickinson,
Massimo Sacchetti

摘要

Purpose

Respiratory frequency (f_R) and tidal volume (V_T) show distinct responses during high-intensity interval training (HIIT) bouts, yet the underlying mechanisms remain unclear. We investigated the effects of hypoxia and hyperthermia on ventilatory responses to HIIT bouts.

Methods

Ten recreationally trained males (mean ± SD: peak oxygen uptake: 3.98 ± 0.62 L/min, age: 28 ± 6 years) performed the same HIIT protocol to exhaustion in three randomized conditions: normobaric hypoxia (HYP, 15% O₂), hyperthermia (HOT, 35 °C, 40% humidity), and control (CON, 18 °C and 40% humidity). Work–recovery phases (30–30 s) were performed at 109% of peak power output from a prior incremental test and 50 W, respectively.

Results

Time-to-exhaustion (TTE) differed (P < 0.05) across CON (18.0 ± 4.4 min), HYP (9.4 ± 2.8 min), and HOT (12.6 ± 3.1 min) conditions. Iso-time f_R was associated with changes in TTE and positively correlated with perceived exertion (P < 0.001; r = 0.85) and aural temperature (P < 0.001; r = 0.58). On average, f_R increased during the work phase and decreased during recovery, primarily driving pulmonary ventilation ( \({\dot{\text{V}}}_{{\text{E}}}\) ) during work–recovery alternations. Conversely, V_T showed a smaller and opposite response, with higher values during recovery. V_T plateaued in all conditions, but higher values were observed in HYP versus CON and HOT, accompanied by higher capillary blood lactate levels and lower blood oxygen saturation.

Conclusions

f_R is associated with changes in exercise tolerance irrespective of the environmental conditions tested and is more closely related to perceived exertion than to aural temperature. f_R primarily drives the \({\dot{\text{V}}}_{{\text{E}}}\) response to high-intensity work–recovery alternations, while V_T appears fine-tuned on f_R levels and the magnitude of metabolic inputs.