Water Vapor Loss From the Respiratory Tract During Outdoor Exercise in the Cold

The water vapor contained in oral expired air was collected during rest and exercise in a subarctic environment in 26 experiments on three men. Heat loss via this route was about 9% of the total energy expenditure. Water vapor loss was directly proportional to ventilation volume. An average (s coefficient) of 32 mg of water was collected from each liter of expired air.