Thermo-effector responses to a 5-day high-intensity cold-acclimation procedure

Sammanfattning: Long-term, repeated exposures to cold might lead to cold adaptation. The study examined, in a small homogeneous group of non-acclimatised men, the inter-individual response to a short-term, high-intensity cold acclimation regimen. In particular, six young (24 - 28 years), healthy men performed 5 daily, whole-body (immersed to the chest for up to 120-min) immersions in 14°C water, during which their thermo-effector responses were evaluated. The study also sought to determine whether, or to what extent, any thermoregulatory modifications induced by the repeated severe cold stress would be transferred to acute moderate cold stress immersions (i.e., “transfer” adaptation). Thus, a few days before and after the acclimation protocol, subjects’ thermoregulatory function was assessed during whole-body immersions in 21°C water. During all immersions, thermal (rectal and skin temperatures), cardiorespiratory (oxygen uptake, mean arterial pressure, heart rate) and perceptual (thermal sensation and comfort, pain, affective valence) responses were monitored. The 5-day cold acclimation regimen caused a hypothermic adaptation, which was characterised by: i) a reduction in the cold-induced elevation of endogenous heat production (i.e., oxygen uptake), which was mainly ascribed to a delay in the activation of shivering, ii) an attenuation in the cold-induced increase of arterial pressure and heart rate, and iii) the alleviation of thermal discomfort. Aside from the blunted pressor response, these thermo-adaptive modifications seemed to be transferrable during exposure to a moderate cold stimulus as well. Still, during both cold provocations, the thermoregulatory adjustments were described by a large inter-individual variability, regarding the direction and the magnitude of the response.