I'm not a doctor or scientist but it's common knowledge that the body, when exposed to extremes, the physiology of the body changes. It adapts to heat, cold, high elevation. Training in the heat, cells start becoming more efficient conserving water, the mind breaks the mental barrier as well from being hot and pushing on. There would be a lot of IV's at first then some then hardly any. Maybe the training is not as intense as before, but in short burst in heat it would have an effect on some level.