Effect of simulated weightlessness on exercise-induced anaerobic threshold

Area of Science:

• Exercise Physiology
• Cardiovascular Physiology
• Deconditioning Syndromes

Background:

• Prolonged bed rest leads to deconditioning, affecting physiological responses to exercise.
• Understanding the impact of deconditioning on the anaerobic threshold is crucial for rehabilitation and performance.
• Head-down bed rest simulates microgravity effects, relevant for spaceflight and clinical populations.

Purpose of the Study:

• To investigate the effects of 10 days of head-down bed rest on the anaerobic threshold (AT) and maximal oxygen uptake (VO2max).
• To assess changes in ventilatory and gas exchange parameters during graded exercise post-bed rest.
• To correlate changes in AT with alterations in plasma and blood volume.

Main Methods:

• Ten healthy males underwent graded supine cycle ergometer tests before and after 10 days of -6° head-down bed rest.
• Ventilation (VE), CO2 output (VCO2), oxygen uptake (VO2), and respiratory exchange ratio (R) were continuously monitored.
• The anaerobic threshold was identified using ventilatory and gas exchange criteria; plasma and blood volumes were measured.

Main Results:

• VO2max decreased by 7.0% after bed rest (p<0.05).
• The anaerobic threshold was significantly reduced in terms of VO2 (from 1.26 to 0.95 L·min⁻¹), %VO2max (from 52.2% to 42.6%), and work rate (from 93 to 65 W).
• Blood volume decreased by 8.8% due to an 11.0% reduction in plasma volume, while red cell volume remained constant.

Conclusions:

• Ten days of head-down bed rest significantly impairs exercise performance by reducing both VO2max and the anaerobic threshold.
• The observed deconditioning is associated with a reduction in plasma volume.
• These findings highlight the substantial physiological impact of short-term inactivity on aerobic capacity and exercise tolerance.