 I talked with Julien Perriard. He's a former triathlete turned exercise physiologist at the University of Canberra in Australia. He says everything feels harder when the riders are heat stressed. What also happens when you're exercising the heat because you have that increase in whole body temperature is that your maximum power, your maximum aerobic capacity or your VO2 max, your VO2 max kind of decreases progressively with hyperthermia.