Time course of physiological and psychological responses in humans during a 20-day severe-cold-acclimation programme

Abstract

The time course of physiological and psychological markers during cold acclimation (CA) was explored. The experiment included 17 controlled (i.e., until the rectal temperature reached 35.5°C or 170 min had elapsed; for the CA-17 session, the subjects (n = 14) were immersed in water for the same amount of time as that used in the CA-1 session) head-out water immersions at a temperature of 14°C over 20 days. The data obtained in this study suggest that the subjects exhibited a thermoregulatory shift from peripheral-to-central to solely central input thermoregulation, as well as from shivering to non-shivering thermogenesis throughout the CA. In the first six CA sessions, a hypothermic type of acclimation was found; further CA (CA-7 to CA-16) led to a transitional shift to a hypothermic-insulative type of acclimation. Interestingly, when the subjects were immersed in water for the same time as that used in the CA-1 session (CA-17), the CA led to a hypothermic type of acclimation. The presence of a metabolic type of thermogenesis was evident only under thermoneutral conditions. Cold-water immersion decreased the concentration of cold-stress markers, reduced the activity of the innate immune system, suppressed specific immunity to a lesser degree and yielded less discomfort and cold sensation. We found a negative correlation between body mass index and Δ metabolic heat production before and after CA.

Figure 1. Research design.

Cold acclimation (CA) protocol–17 head-out cold-water immersions (CA-1 to CA-17) over 20 days.

Figure 2. Cooling time and rectal temperature throughout the cold acclimation.

Cooling time (B) and rectal temperature before (C) and after (A) cooling. * P<0.05, compared with CA-1; # P<0.05, compared with CA-17. Values are means ± SEM.

Figure 3. Rate of decrease in rectal temperature during cooling throughout cold acclimation.

* P<0.05, compared with CA-1. Values are means ± SEM.

Figure 4. Skin temperature throughout cold acclimation.

Skin temperature before (A) and after (B) body cooling, and change from before to after body cooling (C). * P<0.05, compared with the CA-1. Δ T_sk  =  mean difference between T_sk before and T_sk after cold exposure. Values are means ± SEM.

Figure 5. Body temperature gradient change before (CA-1 session) and after (CA-16 and CA-17 sessions) cold acclimation.

* P<0.05, compared with CA-1; # P<0.05, compared with CA-16. Values are means ± SEM.

Figure 6. Heart rate (HR) throughout cold acclimation.

HR at rest and during cooling (A), and change from at rest to during cooling (B). * P<0.05, compared with CA-1. Δ HR  =  mean difference between HR before and HR during cold exposure. Values are means ± SEM.

Figure 7. VO₂ and metabolic heat production (MHP) throughout cold acclimation.

VO₂ (A) and MHP (B). * P<0.05, compared with CA-1. Values are means ± SEM.

Figure 8. Hyperventilation throughout cold acclimation.

* P<0.05, compared with CA-1. Values are means ± SEM.

Figure 9. Shivering, thermal and comfort sensation throughout cold acclimation.

Shivering (A), thermal (B) and comfort (C) sensation. * P<0.05, compared with CA-1. Values are means ± SEM.

Figure 10. Shivering sensation during the first 20(CA-1) and after cold acclimation (CA-16 and CA-17).

* P<0.05, compared with a 5 min; # P<0.05, compared with the CA-1 session; Values are means ± SEM.