Aerobic exercise performance is reduced following prolonged cold-water immersion

Background: We tested the hypotheses that self-paced aerobic exercise performance is reduced following four hours of cold-water immersion when breathing air and further reduced when breathing 100% oxygen (O₂). Nine healthy adults (four women; age 24 ± 3 years; body fat 17.9 ± 6.4 %; VO_2max 48 ± 9 mL·kg·minute^-1) completed three visits: a no-immersion control trial and two experimental trials consisting of a four-hour cold-water immersion (20.1±0.3°C) either breathing air (FIO2 = 0.21) or O₂ (FIO₂ = 1.0). During the no-immersion control trial and following immersion in the experimental trials, subjects first completed a 60-minute ruck-march carrying 20% of body mass in a rucksack, immediately followed by an unweighted, self-paced 5-km time trial on a motorized treadmill. Core temperature, heart rate, and rating of perceived exertion were recorded every 1,000 meters during the 5-km time trial. Data are presented mean ± SD. Time trial performance was reduced following immersion in both the 100% O₂ trial (32 ± 6 minutes; p=0.01) and air trial (32 ± 5 minutes; p=0.01) compared to the control trial (28 ± 4 minutes). However, there was no difference between the 100% O₂ and air trials (p=0.86). Heart rate, core temperature, and rating of perceived exertion increased during the time trial (time effect: p<0.01), but were not different between trials (trial effect: p≥0.33). These findings suggest that prolonged cold-water immersion attenuates self-paced aerobic exercise performance, but does not appear to be further affected by breathing gas type.