Peak exercise oxygen uptake during and following long-duration spaceflight

Area of Science:

• Space physiology
• Human physiology in microgravity
• Cardiovascular health in astronauts

Background:

• Long-duration spaceflight poses risks to astronaut health, including potential declines in aerobic capacity.
• Understanding changes in maximal oxygen uptake (V̇o2peak) is crucial for astronaut health and mission success.

Purpose of the Study:

• To measure changes in aerobic capacity (V̇o2peak) during and after long-duration International Space Station (ISS) missions.
• To identify factors influencing V̇o2peak maintenance or decline in astronauts.

Main Methods:

• Assessed V̇o2peak using cycle ergometry at multiple time points: pre-flight, early in-flight, periodically during flight, and post-flight (R+1, R+10, R+30).
• Measured expired metabolic gas fractions, ventilation, and heart rate (HR) during tests.
• Analyzed data using mixed-model linear regression.

Main Results:

• V̇o2peak decreased by approximately 17% early in-flight, gradually increased during the mission, but did not return to pre-flight levels for most astronauts.
• V̇o2peak was lower on recovery days R+1 and R+10 compared to pre-flight, but recovered by R+30.
• Peak HR remained similar to pre-flight levels throughout the mission and recovery.
• Seven astronauts maintained or exceeded pre-flight V̇o2peak levels, with some engaging in higher intensity exercise or having lower pre-flight aerobic capacity.

Conclusions:

• While aerobic capacity (V̇o2peak) can decrease during long-duration spaceflight, it is not universally experienced.
• Aerobic deconditioning is not an inevitable consequence of long-duration ISS missions.
• Individual factors, including exercise intensity and baseline fitness, may influence V̇o2peak maintenance.