Abstract
To assess the impact of thoracic load carriage on the physiological response to exercise in hypoxia. Healthy males (n = 12) completed 3 trials consisting of 45 min walking in the following conditions: (1) unloaded normoxia (UN; F(I)O(2):20.93%); (2) unloaded hypoxia (UH; F(I)O(2):~13.0%); and (3) loaded hypoxia (LH; 29.5 kg; F(I)O(2):~13.0%). Intensity was matched for absolute VO(2) (2.0 ± 0.2 L·min(-1)) across conditions and relative VO(2) (64.0 ± 2.6 %VO(2max)) across hypoxic conditions. With LH versus UH, there were increases in breathing frequency (5-11 breaths·min(-1); p < 0.05) and decreases in tidal volume (10%-18%; p < 0.05) throughout exercise due to reductions in end inspiratory lung volumes (p < 0.05). Consequently, deadspace (11%-23%; p < 0.05) and minute ventilation (7%-11%; p < 0.05) were increased starting at 20 and 30 min, respectively. In addition, LH increased perceived exertion/dyspnea and induced inspiratory (~12%; p < 0.05 vs. UN) and expiratory (~10%; p < 0.05 vs. pre-exercise) respiratory muscle fatigue. Expiratory flow limitation was present in 50% of subjects during LH. Cardiac output and muscle oxygenation were maintained during LH despite reduced stroke volume (6%-8%; p < 0.05). Finally, cerebral oxygenated/total hemoglobin were elevated in the LH condition versus UH starting at 15 min (p < 0.05). Thoracic load carriage increases physiological strain and interferes with the compensatory response to hypoxic exposure.