Human thermoregulation in cold environment and the mechanisms of accidental hypothermia during exercise

Abstract

Sports and activities that take place in nature, such as marathons, open-water swimming, mountain climbing, and underwater leisure activities, have become popular in recent years. When these sports and leisure activities are performed in cold environments with low ambient temperatures or cold water, thermoregulatory responses such as cutaneous vasoconstriction, shivering and non-shivering thermogenesis occur to prevent a decrease in body core temperature. Furthermore, during exercise, heat production in active muscles occurs with exercise in addition to the thermoregulatory responses, and it is thought that the body core temperature is unlikely to drop. However, “accidental hypothermia,” an excessive drop in body core temperature (<35°C), occurs during leisure activities and exercise in cold environments. Because accidental hypothermia occurs despite heat production associated with exercise in addition to the thermoregulatory responses, it is thought that “specific factors” that differ from the normal heat balance are responsible for the onset of hypothermia during exercise and have been investigated in several studies to date. This review aims to help humans safely perform sports and activities in cold environments and achieve high performance. We will review the thermoregulatory responses that occur in cold environments and the effects of exercise on them, and consider the mechanisms of hypothermia that occur even during exercise and how to prevent it.