Interaction Between Ambient Temperature, Hypoxia, and Load Carriage on Respiratory Muscle Fatigue

BACKGROUND: While respiratory muscle fatigue is present following load carriage activity at sea level, the effect of environmental conditions on respiratory strength while undertaking load carriage is unknown. METHODS: The effect of thoracic load carriage during walks (5.5 km) in four environments [(thermo-neutral sea level (SL), 10 degrees C (C), 4300 m (H) and 4300 mat 10 degrees C (HC)] was evaluated on respiratory muscle fatigue. Ten subjects completed eight self-paced randomized treadmill walks comprising a variety of gradients, unloaded and loaded (18.2 kg), across the four environments. Respiratory muscle strength was measured via maximal inspiratory pressure (P-lmax) and expiratory pressure (P-Emax) assessments. RESULTS: Submaximal walking in HC elicited respiratory muscle fatigue when compared to SL. Inspiratory muscle fatigue was independent of load. The relative change in P-lmax from baseline was significantly greater in HC compared to SL (9.6% vs. 1.3%). P-Emax showed a significant reduction during HC (-22.3 cmH(2)O, -14.4%) when compared to the other three environments. CONCLUSION: These results highlight the need to focus on respiratory muscle strength in preparation for exercise in cold hypoxic conditions.