Repeated Short Cold-water Immersions Are Sufficient To Habituate To The Cold, But Do Not Lead To Adaptations During Exercise In Normobaric Hypoxia

PURPOSE: To assess the effects of repeated cold-water immersions (CWI) on respiratory, metabolic, and sympathoadrenal responses to graded exercise in hypoxia. METHODS: 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). RESULTS: 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<0.05), VT (CWI #1: 1.3 ± 0.4 vs CWI #6: 1.1 ± 0.4 L)(p<0.05), and VE/VO2 (CWI #1: 53.5 ± 24.1 vs CWI #6: 41.6 ± 20.5)(p<0.05) during subsequent CWI. However, CWI had no effect on exercise in hypoxia as there were no changes in pulmonary (VE, VT, VE/VO2)(p>0.05) or metabolic (VO2, SmO2, SpO2) (p>0.05) variables across multiple workloads following repeated CWI. Finally, the post exercise plasma epinephrine was lower after CWI compared to before (103.3 ± 43.1; 73.4 ± 34.6 pg/ml) (p<0.05), with no change in pre exercising values (75.4 ± 30.7; 72.5 ± 25.9 pg/ml). CONCLUSIONS: Six CWI of five minutes, twice daily for three consecutive days resulted in cold habituation. This was evidenced by decreased VE, VT, and VE:VO2 during successive CWI. In addition, CWI lowered post hypoxic exercise epinephrine concentration. However, CWI did not realize any meaningful respiratory, metabolic, or perceptual changes during exercise in acute hypoxia, over a wide range of exercise intensities.