Many of us are facing training on hot days this time of the year. I go out of my way to avoid it by getting up early. My brother gets up at 4:30 AM in the summers in Phoenix to avoid triple digit temperatures. But there’s evidence training in the heat actually has benefits for improving performance.
I saw this on Alex Hutchinson’s online training blog (“sweat science”) at Outside Magazine, referring to a recent study which gives a hypothesis for an interesting mechanism. Training in the heat increases your total blood volume, which in turn lowers your hematocrit level, which tracks the percentage of red blood cells in your blood. When it drops, the body responds by pumping out natural Erythropoietin (EPO) to cause more red blood cells to be produced. More blood cells is a good thing for aerobic performance because it boosts oxygen carrying capacity.
Anyone who has followed professional cycling is unfortunately well informed about epo and hematocrit. Artificial epo is a banned substance, and one of the ways of detecting drug abuse is detecting too high a level of hematocrit. An upper limit was placed because too high a level is dangerous, your blood gets “sludgy” and athletes have died from exerting with this condition.
But training in the heat is a safe and natural way to boost performance. The downside is that it takes hard training in hot weather for at least five weeks. For those slogging through the heat this summer, you can take comfort that it will get you fitter by fall.