REPEATED SHORT COLD-WATER IMMERSIONS ARE SUFFICIENT TO HABITUATE TO THE COLD, BUT DO NOT LEAD TO ADAPTATIONS DURING EXERCISE IN NORMOBARIC HYPOXIA.

We sought to assess the effects of repeated cold-water immersions (CWI) on respiratory, metabolic, and sympathoadrenal responses to graded exercise in hypoxia. 16 (2 female) participants (age: 21.2 ± 1.3 years; body fat: 12.3 ± 7.7 %; body surface area 1.87 ± 0.16 m2, VO2peak: 48.7 ± 7.9 mL/kg/min) underwent 6 CWI in 12.0 ± 1.2° C. Each CWI was 5 minutes, twice daily, separated by ≥4 hours, for 3 consecutive days, during which metabolic data were collected. The day before and after the repeated CWI intervention, participants ran in normobaric hypoxia (FIO2 = 0.135) for 4 minutes at 25%, 40%, 60%, and 75% of their sea level peak oxygen consumption (VO2peak). CWI had no effect on VO2 (p>0.05), but reduced the VE (CWI #1: 27.1 ± 17.8 vs CWI #6: 19.9 ± 12.1 L/min)(p<0.01), VT (CWI #1: 1.3 ± 0.4 vs CWI #6: 1.1 ± 0.4 L)(p<0.01), and VE/VO2 (CWI #1: 53.5 ± 24.1 vs CWI #6: 41.6 ± 20.5)(p<0.01) during subsequent CWI. Further, post exercise plasma epinephrine was lower after CWI compared to before (103.3 ± 43.1; 73.4 ± 34.6pg/ml) (p=0.03), with no change in pre exercising values (75.4 ± 30.7; 72.5 ± 25.9 pg/ml). While these changes were noteworthy, it is important to acknowledge there were no changes in pulmonary (VE, VT, VE/VO2) or metabolic (VO2, SmO2, SpO2) variables across multiple hypoxic exercise workloads following repeated CWI. CWI habituated participants to cold water, but this did not lead to adaptations during exercise in normobaric hypoxia.