Heat stress increases ammonia accumulation during exercise in humans

Seven men were studied during 40 min of exercise at 70% VO2 peak, in an environmental chamber maintained at either 20 or 40 degrees C, to examine the effect of heat stress on ammonia metabolism during exercise. Heart rate and rectal and muscle temperatures were higher during exercise in the heat, while no differences were observed in pulmonary oxygen uptake or respiratory exchange ratio. Plasma ammonia levels and muscle ammonia accumulation were higher during exercise at 40 degrees C compared with 20 degrees C. Such metabolic alterations may be associated with reduced performance during exercise in the heat.