Heat training after seven to 14 days acts as a natural performance enhancer. It increases blood plasma volume. It's basically an EPO.

Heat is the cheapest legal performance enhancer available to a runner. Train in it deliberately for seven to fourteen days and your blood plasma volume expands, commonly 4 to 15 percent. More plasma means more blood to send to skin and muscle at once, a lower heart rate at the same workload, and a body that runs cooler under stress. That adaptation shows up within the first week.

The literature and my legs agree on the timeline. The Périard review puts the plasma expansion and the cardiovascular relief inside days, with the fuller adaptation stack landing across two weeks. My claim that it is basically an EPO is only half a joke. It raises your blood's carrying capacity, and nobody can ban it.

Racing in heat is a different skill from adapting to it. When it is 95 plus, the plan changes before the gun. I give back a full minute per mile on pace, accept the higher heart rate as the cost of doing business, and run ice bandanas at the neck and groin, the two spots where cooling actually reaches the bloodstream.

That is how a 100 degree Finger Lakes 50K becomes a podium instead of a medical tent. The runners who blew up that day were racing the pace from their cool spring training block. The heat does not negotiate. You adapt beforehand and concede to it during, and it hands the race to you at the end.