Rapidity of responding to a hypoxic challenge during exercise

Area of Science:

• Exercise Physiology
• Sports Science
• Human Performance

Background:

• Optimizing exercise performance requires rapid power output (PO) modification in response to stimuli.
• Understanding the regulation of PO during exercise necessitates knowing the speed of these modifications.
• The rapidity of PO adjustment to hypoxic challenges remains largely unestablished.

Purpose of the Study:

• To determine the rapidity of changes in power output (PO) in response to a hypoxic challenge.
• To investigate if changes in PO are linked to alterations in arterial oxygen saturation (SaO2).

Main Methods:

• Well-trained cyclists completed 5-km time trials under randomized conditions.
• Participants switched from breathing room air to hypoxic (15% O2) or room air (21% O2) at 2 km, returning to room air at 4 km.
• Time delays for decreases and recovery in SaO2 and PO, and half-times, were compared between conditions.

Main Results:

• Significant differences in mean SaO2 and PO were observed between hypoxic and control conditions between 2 and 4 km.
• No significant difference was found in the time delay for SaO2 and PO changes, nor in their recovery times.
• The half-times for decreases in SaO2 and PO were not significantly different.

Conclusions:

• Modifications in power output (PO) during hypoxic exercise are related to the development of arterial hypoxemia.
• These PO adjustments begin approximately 30 seconds after the onset of the hypoxic stimulus.