Maximal muscle activation is not limited by pulmonary ventilation in chronic hypoxia

This study was conducted to test the hypothesis that inhibitory reflexes from respiratory centres in the brain or respiratory muscles limit the central motor drive to limb muscles during exhaustive exercise in chronic hypoxia. Experiments were performed on five members of an expedition to the Himalayas, following 56-81 days at altitudes of 5200-7500 m. During the last minute of exhaustive maximal two-legged cycling with and without 4% CO2 inhalation performed on different days, repeated maximal voluntary handgrip contractions (MVC) over 60 s (5 s contraction, 5 s rest; x 6) were performed at rest and exhaustive exercise MVC or rate of decay of MVC was unaffected by simultaneous engagement of a major fraction of the muscle mass (leg muscles) and a very high pulmonary ventilation. With 4% CO2, peak pulmonary ventilation during the exhaustive exercise increased further by 41 L min-1 (140-181 L min-1; P < 0.05) without affecting the handgrip strength. These findings suggest that during exhaustive exercise of large muscle groups in chronic hypoxia, both maximal voluntary contraction force and dynamic muscle contractile force are not limited by extreme activation of respiratory centres or muscles.