Author(s): HORIUCHI, M., MURAKAMI, T., FUKUOKA, Y., OLIVIER, G., Institution: NATIONAL INSTITUTE OF FITNESS AND SPORTS IN KANOYA: KANOYA TAIIKU DAIGAKU, Country: JAPAN, Abstract-ID: 1296

INTRODUCTION:
Combining repeated high-intensity exercise with hypoxia has gained attention given its potential to induce greater physiological adaptations [1]. However, reduced inspired oxygen fraction constrains oxygen transport from air to muscle mitochondria, potentially limiting exercise capacity. Neuromuscular fatigue under hypoxia may involve both peripheral (active muscle) and central (central nervous system) mechanismhttps://sport-science.org/index.php/submission-2026/abstract-submission/how-to-submits [2]. Therefore, the aim of the present study was to examine active muscle (vastus lateralis) and cerebral (prefrontal cortex) oxygenation during repeated maximal cycling in hypoxia and normoxia using near-infrared spectroscopy. We hypothesized that larger hypoxia-related performance decrements would correspond with lower muscle and cerebral oxygenation levels.
METHODS:
Ten male middle-distance runners (age: 20±1 years; 800 m season best: 113.3±3.9 s) completed a repeated Wingate protocol under hypoxia (inspired oxygen fraction: 0.145) and normoxia using a randomized crossover design. The exercise protocol involved four 30-second all-out cycling bouts at maximal cadence. The exercise intensity was set to 7.5% of body weight for the first bout and progressively reduced to 6.5%, 5.5%, and 4.5% to maintain maximal effort. Each bout was separated by 4-minute of unloaded pedaling at 50 rpm (0 watts).
RESULTS:
Average mean power output across the four sets was ~4% higher in normoxia (474±24 W) than in hypoxia (455±24 W, P=0.007).
During exercise, hypoxia elicited greater muscle deoxygenation and total hemoglobin in the vastus lateralis, alongside lower tissue oxygen saturation in both the vastus lateralis and prefrontal cortex (all P<0.05). During the 4-min recovery periods, muscle and cerebral reoxygenation were greater in normoxia than hypoxia (P=0.055 and P<0.001, respectively). Reductions in power output under hypoxia correlated with increased cerebral deoxygenation during exercise (r=-0.452, P=0.011) and recovery (r=0.440, P=0.046), whereas those marginally correlated with increased muscle de- (r=-0.268, P=0.145) and re-oxygenation (r=0.413, P=0.063).
CONCLUSION:
These results suggest that individuals with smaller reductions in cerebral oxygenation during exercise and recovery are better able to maintain repeated high-intensity exercise performance., which was supported by a previous finding, showing that limited oxygen availability decreased central motor drive, thereby limiting performance in hypoxia [3]. Cerebral oxygenation responses appear to be a key determinant of repeated high-intensity exercise performance in hypoxia.
References
[1] Girard et al. (2020) Front Sports Act Living, 2, 26. doi:10.3389/fspor.2020.00026
[2] Fan and Kayser. (2016) High Alt Med Biol, 17(2):72-84.
[3] Amann et al. (2007) J Physiol, 581: 389-403.