Exercise intolerance at high altitude (5050 m): critical power and W'

Area of Science:

• Exercise Physiology
• Altitude Physiology
• Human Performance

Background:

• The relationship between work rate and tolerable duration is crucial for understanding exercise capacity.
• This relationship has not been previously studied at high altitude (HA).

Purpose of the Study:

• To investigate the effects of HA on the hyperbolic relationship between work rate (WR) and its tolerable duration (t(LIM)).
• To assess exercise tolerance and physiological responses at HA compared to sea level (SL).

Main Methods:

• Six subjects performed symptom-limited cycle-ergometry at HA (5050 m) and SL.
• Tests included an incremental exercise test (IET) and three constant-WR tests at varying percentages of maximal WR.
• Measurements included WR, t(LIM), breathing reserve, and dyspnea levels (Borg scale).

Main Results:

• The power asymptote (CP) and curvature constant (W') were significantly reduced at HA compared to SL.
• HA resulted in compromised breathing reserve across all tested WR intensities.
• Subjects reported near-maximal dyspnea levels at HA, particularly at higher work rates.

Conclusions:

• Reduced oxygen availability at HA likely contributes to the lower CP.
• The reduction in W' may be due to decreased muscle-venous oxygen storage, compounded by ventilatory limitation and dyspnea.
• Exercise tolerance is substantially impaired at HA due to these physiological constraints.