Combined effects of exposure to hypoxia and cool on walking economy and muscle oxygenation profiles at tibialis anterior

ABSTRACT

We investigated combined effects of ambient temperature (23°C or 13°C) and fraction of inspired oxygen (21%O₂ or 13%O₂) on energy cost of walking (C_w: J·kg⁻¹·km⁻¹) and economical speed (ES). Eighteen healthy young adults (11 males, seven females) walked at seven speeds from 0.67 to 1.67 m s⁻¹ (four min per stage). Environmental conditions were set; thermoneutral (N: 23°C) with normoxia (N: 21%O₂) = NN; 23°C (N) with hypoxia (H: 13%O₂) = NH; cool (C: 13°C) with 21%O₂ (N) = CN, and 13°C (C) with 13%O₂ (H) = CH. Muscle deoxygenation (HHb) and tissue O₂ saturation (StO₂) were measured at tibialis anterior. We found a significantly slower ES in NH (1.289 ± 0.091 m s⁻¹) and CH (1.275 ± 0.099 m s⁻¹) than in NN (1.334 ± 0.112 m s⁻¹) and CN (1.332 ± 0.104 m s⁻¹). Changes in HHb and StO₂ were related to the ES. These results suggested that the combined effects (exposure to hypoxia and cool) is nearly equal to exposure to hypoxia and cool individually. Specifically, acute moderate hypoxia slowed the ES by approx. 4%, but acute cool environment did not affect the ES. Further, HHb and StO₂ may partly account for an individual ES.

KEYWORDS:

• High-altitude
• interactive effect
• mountain climbing
• muscle O₂ extraction
• muscle blood flow

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Japan Scoety for the Promotion of Science;[26440268, 26650175, and 26440266].