This study investigated whether hypoxia superimposed on exercise-induced arterial hypoxaemia exacerbates the exercise-induced diaphragmatic fatigue in these athletes. Eight trained cyclists completed four 5 min exercise tests leading to different levels of end-exercise SaO2 via variations in inspired O2 fraction. Measurements were made at corresponding intensities in order to produce the same tidal volume, breathing frequency and respiratory muscle load at each FiO2. The results demonstrated a greater amount of diaphragmatic fatigue in hypoxia at lower leg work rates (presumably requiring smaller leg blood flow compared with normoxia at higher leg work rates). This suggests that when ventilatory muscle load is similar between normoxia and hypoxia, hypoxia exaggerates diaphragmatic fatigue in spite of potentially greater respiratory muscle blood flow availability.
Journal of Physiology, 2007, 581, 1, 299-308.