Key result
Hypobaric hypoxia significantly increased the time required to complete a 250-kJ cycling time-trial by 7.5% compared to normobaric hypoxia, driven by impaired systemic and prefrontal cortex oxygenation.
Why the study?
It remains unclear how normobaric versus hypobaric hypoxia with identical ambient oxygen pressure differentially affect cerebrovascular and muscular regulation interplay during self-paced aerobic exercise.
Does hypobaric hypoxia compared to normobaric hypoxia alter cerebrovascular regulation, muscular activation, and pacing strategies during a self-paced endurance exercise in healthy trained males?
RCT (n=16)
Single-blind
Randomized crossover
No
Does hypobaric hypoxia compared to normobaric hypoxia alter cerebrovascular regulation, muscular activation, and pacing strategies during a self-paced endurance exercise in healthy trained males?
Effect estimate: 7.5% higher (95% CI 3.2-11.7)
Absolute Event Rate: 1379% vs 1286%
p-value: p=<0.01
Hypobaric hypoxia impairs endurance performance and pacing more than normobaric hypoxia at the same oxygen pressure, likely due to a complex interplay between systemic alterations and cerebral oxygenation.
Hypobaric hypoxia impairs endurance performance more than normobaric hypoxia at matched inspired O2; extends altitude research by isolating barometric effects on cerebral oxygenation and pacing.
Purpose: Hypoxia is one major environmental factor, supposed to mediate central motor command as well as afferent feedbacks at rest and during exercise. By using a comparison of normobaric (NH) and hypobaric (HH) hypoxia with the same ambient pressure in oxygen, we examined the potential differences on the cerebrovascular and muscular regulation interplay during a self-paced aerobic exercise. Methods: Sixteen healthy subjects performed three cycling time-trials (250 kJ) in three conditions: HH, NH and normobaric normoxia (NN) after 24 h of exposure. Cerebral and muscular oxygenation were assessed by near-infrared spectroscopy, cerebral blood flow by Doppler ultrasound system. Gas exchanges, peripheral oxygen saturation, power output and associated pacing strategies were also continuously assessed. Results: The cerebral oxygen delivery was lower in hypoxia than in NN but decreased similarly in both hypoxic conditions. Overall performance and pacing were significantly more down-regulated in HH versus NH, in conjunction with more impaired systemic (e.g . saturation and cerebral blood flow) and prefrontal cortex oxygenation during exercise. Conclusions: The difference in pacing was likely the consequence of a complex interplay between systemic alterations and cerebral oxygenation observed in HH compared to NH, aiming to maintain an equivalent cerebral oxygen delivery despite higher adaptive cost (lower absolute power output for the same relative exercise intensity) in HH compared to NH.
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Rupp et al. (2022) conducted an RCT in Healthy trained cyclists (n=16). Hypobaric hypoxia vs. Normobaric hypoxia (3,450 m simulated altitude) was evaluated on Mean duration to complete 250-kJ time-trial (7.5% higher, 95% CI 3.2-11.7, p=<0.01). Hypobaric hypoxia significantly increased the time required to complete a 250-kJ cycling time-trial by 7.5% compared to normobaric hypoxia, driven by impaired systemic and prefrontal cortex oxygenation.
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