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. 2021 Oct;121(10):2869-2878.
doi: 10.1007/s00421-021-04738-w. Epub 2021 Jun 30.

Effects of combined hot and hypoxic conditions on muscle blood flow and muscle oxygenation during repeated cycling sprints

Keiichi Yamaguchi  1 , Daichi Sumi  2 , Nanako Hayashi  1 , Naoki Ota  1 , Koki Ienaga  1 , Kazushige Goto  3
Affiliations

Effects of combined hot and hypoxic conditions on muscle blood flow and muscle oxygenation during repeated cycling sprints

Keiichi Yamaguchi et al. Eur J Appl Physiol. 2021 Oct.

Abstract

Purpose: The purpose of the present study was to determine muscle blood flow and muscle oxygenation during repeated-sprint exercise under combined hot and hypoxic conditions.

Methods: In a single-blind, cross-over research design, 11 active males performed three sets of 5 × 6-s maximal sprints with 30-s active recovery on a cycling ergometer under control (CON; 23 °C, 50% rH, 20.9% FiO2), normobaric hypoxic (HYP; 23 °C, 50% rH, 14.5% FiO2), or hot + normobaric hypoxic (HH; 35 °C, 50% rH, 14.5% FiO2) conditions. The vastus lateralis muscle blood flow after each set and muscle oxygenation during each sprint were evaluated using near-infrared spectroscopy methods.

Results: Despite similar repeated-sprint performance among the three conditions (peak and mean power outputs, percent decrement score), HH was associated with significantly higher muscle blood flow compared with CON after the first set (CON: 0.61 ± 0.10 mL/min/100 g; HYP: 0.81 ± 0.13 mL/min/100 g; HH: 0.99 ± 0.16 mL/min/100 g; P < 0.05). The tissue saturation index was significantly lower in HYP than in CON during the latter phase of the exercise (P < 0.05), but it did not differ between HH and CON.

Conclusion: These findings suggest that a combination of normobaric hypoxia and heat stress partially facilitated the exercise-induced increase in local blood flow, but it did not enhance tissue desaturation.

Keywords: Cycling; Heat stress; Near-infrared spectroscopy; Normobaric hypoxia; Repeated-sprint.

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