

“And so your ability to have your body withstand any type of stress will make you a little bit more resilient to things that are unexpected.” “If you can withstand heat, you’re able to withstand stress,” Hew-Butler says. Pressure sensors in the heart act as a control, prompting urine output when there’s too much water in circulation, or constricting vessels when there’s not enough. Blood vessels dilate, increasing the water in our circulation, and making it easier for evaporative cooling via sweat. Drinking water, as well as heat exposure, cause a temporary increase in blood plasma volume. Physiologist Tamara Hew-Butler is an expert in overhydration, a trend that has killed athletes in recent years. One study even examined the most cooling drinks, awarding top status to the humble gas station Slurpee, whose icy particles cool the body from the inside out.


New performance equipment that allows athletes to pack ice around the head, neck, and torso during races has helped. There are also hard limits to how much heat humans can endure. (Yes, this means your air conditioning could, technically, be considered a fitness device.) Plus, the constant presence of heat eventually stops triggering heat shock proteins when we adapt to it. The body needs periods of rest to recover and rebuild after stress. Constant heat means constant stress, and that will have a detrimental impact akin to an athlete overtraining and risking injury or worse. This doesn’t mean a warming planet will be favorable to human health, even though prolonged heat exposure should increase heat tolerance. Like exercise, heat exposure can be a positive stressor that activates helpful heat shock proteins, lowers blood pressure, and can help prevent and even treat cardiovascular, metabolic, and autoimmune diseases like rheumatoid arthritis and fibromyalgia. Heat holds promise for everyone from ICU inpatients to runners slogging through Death Valley. Athletes are looking for an edge, and heat can give them that, even if they don’t compete in scorching temperatures. Watts is part of a new wave of elite athletes using heat to sharpen their training, as extreme athletic challenges become harder, the planet gets hotter, and sport regulators are increasingly screening for and banning performance-enhancing gear and supplements. “One day they took my core temperature way up, to just below 40 degrees for me to feel what it was like in the danger zone of overheating,” she says.
