Thermal tolerance following artificially induced polycythaemia

Area of Science:

• Exercise Physiology
• Environmental Physiology
• Human Performance

Background:

• Polycythaemia is known to enhance physical performance by increasing oxygen transport.
• Potential benefits of polycythaemia on thermoregulation, particularly heat dissipation, have been suggested.
• Understanding these effects is crucial for optimizing performance in hot environments.

Purpose of the Study:

• To investigate the impact of polycythaemia on thermoregulatory function during heat stress in trained men.
• To determine if induced polycythaemia improves the body's ability to manage heat during exercise.
• To assess changes in physiological responses related to heat strain and dissipation.

Main Methods:

• Five trained male subjects underwent three-phase heat stress trials (rest, cycling at 30% Wpeak, cycling at 45% Wpeak) under normocythaemic and polycythaemic conditions.
• Polycythaemia was induced by reinfusing autologous red blood cells, significantly increasing arterial oxygen transport.
• Physiological parameters including cardiac frequency, auditory canal temperature, sweat onset, sweat rate, and skin blood flow were measured.

Main Results:

• Polycythaemia significantly reduced thermal strain, evidenced by lower cardiac frequency and auditory canal temperatures.
• Subjects exhibited more rapid forearm sweat onset and elevated forearm sweat rate sensitivity.
• Despite reduced skin blood flow, polycythaemia enhanced thermoregulation through improved sweating responses, leading to greater thermal tolerance.

Conclusions:

• Induced polycythaemia enhances thermoregulatory function in trained men during heat stress.
• Improvements in thermoregulation are primarily mediated by altered sweating patterns, not increased cutaneous blood flow.
• Polycythaemia confers greater thermal tolerance during exercise in the heat, alongside improved oxygen transport.