The influence of hydration state on thermoregulation during a 161-km ultramarathon In general, it is assumed that a loss of more than 2 kg of body weight increases the risk of hyperthermia in an endurance burden.In this study, an American group has studied whether a loss of two and more kg body weight leads to an increase in body core temperature. For thirty runners at a 100-mile run, body weight and body core temperature were measured before, during and after the barrel.It showed that the body core temperature had no connection with the change in body weight or the closing time.On the other hand, there was a connection between the change in body weight and the competition time by the fastest runners the most weight losses. Also important was the realization that a decrease of more than 3% body weight does not lead to an increase in body core temperature.
It must be advised that there is no reason to drink tons of fluid during an ultramarathon in the opinion one could counteract hyperthermia. The very interesting work can be found under https://pubmed.ncbi.nlm.nih.gov/27258701/