Studies have found that, in addition to an increased rate of perspiration, training in the heat can increase an athlete’s blood plasma volume (which leads to better cardiovascular fitness), reduce overall core temperature, reduce blood lactate, increase skeletal muscle force, and, counterintuitively, make a person train better in cold temperatures. In fact, heat acclimation may actually be more beneficial than altitude training in eliciting positive physiological adaptations, says Santiago Lorenzo, a professor of physiology at Lake Erie College of Osteopathic Medicine and a former decathlete at the University of Oregon.