Acute Exposure to Cold Air and Metabolic Responses to Exercise

Abstract

Acute exposure of the whole body to cold air activates thermoregulatory mechanisms which may influence the physiological responses to exercise. Interactions between cold stress and exercise greatly depend on the intensity of cold stimulation. During exposure to moderate cold (MC) peripheral vasoconstriction shifts part of the blood from the periphery to the core, increasing the central volume and the ventricular filling. When an incremental exercise is performed in MC, the persistence of cutaneous vasoconstriction alters the cardiovascular pattern. Moreover, a delayed onset of the increase in plasma lactate concentration (LA) is found and LA remains lower for submax-imum exercise intensities. Simultaneously a greater plasma norepinephrine (NA) response is observed. In addition to cutaneous vasoconstriction shivering thermogenesis occurs during exposure to severe cold (SC) which increases heat production. During incremental exercise, the oxygen consumption (V̇O₂) and the expired minute ventilation (V̇E) are higher for each exercise intensity. However the ventilatory equivalent (V̇O₂/V̇O₂) does not change significantly. The increased ventilatory response seems to remain a pure reaction to increasing metabolic demand. The ventilatory threshold occurs at the same exercise intensity but at a higher V̇O₂ and V̇E than in warm conditions. According to the intensity of cold stress the V̇O₂ level may be similar, increased or decreased at exhaustion. The LA is higher for light exercise intensities, lower for heavy exercise intensities and recovery. Simultaneously a greater NA was found with no change in plasma epinephrine response.

Key words

Thermogenesis - shivering - catecholamines - lactate