High-altitude exercise performance and acute mountain sickness unchanged following cold water habituation

Cross stress adaptation (CA) refers to the induction of physiological adaptation to one stimulus, such as cold water, to adaptively influence the physiological response to another novel stimulus, such as hypoxia. This study sought to determine if cold-hypoxia CA, induced by repeat cold-water immersion (CWI) and compared with a thermoneutral water (TN) control, could reduce resting and submaximal exercise physiologic strain, improve exercise performance, and decrease the incidence and severity of acute mountain sickness (AMS) symptoms during a 29 h exposure to hypobaric hypoxia (∼4,100 m). Cold ventilatory habituation was achieved, evidenced by an ∼20% reduction in peak minute ventilation (V̇e) and ∼31% reduction in 10 min average V̇e with six, 10-min 12°C water immersions. At 3 h of hypobaric hypoxia, an exercise bout at 50% peak oxygen uptake (V̇o_2peak) elicited greater ventilation (+3.8 [0.8-6.7] L·min^-1, P = 0.014) with no concomitant improvement of [Formula: see text] (TN: 76 ± 4 vs. CWI: 76 ± 4%, P > 0.05) following CWI. Exercise heart rate was also elevated following CWI compared with TN, irrespective of altitude exposure duration (+5 [1-8] beats·min^-1, P = 0.030). Two-mile time trial performance and AMS symptomology both were unchanged by repeated CWI compared with TN. Habituation to repeated cold-water immersion does not advantageously cross adapt those subsequently exposed to hypobaric hypoxia. Instead, CWI heightened early altitude ventilatory and cardiovascular strain during submaximal exercise.NEW & NOTEWORTHY Existing literature suggests cold habituation is capable of cross-adapting submaximal exercise ventilatory, cardiac, and catecholamine responses with normobaric hypoxia. No data exists investigating cold-to-altitude cross adaptation within real-world applicable conditions of hypobaric hypoxia. This investigation suggests that habituation to repeated cold-water immersion does not advantageously cross adapt those subsequently exposed to hypobaric hypoxia.