As the planet warms, thanks to the myopic and greedy nature of humans, we must all become used to operating at greater temperatures. Through careful observation of my physiology, I have established a protocol to allow me to run for over an hour at 33º, and the limiting factor is my fitness, not the environment.

Tools

The core tools are a CORE body temperature sensor, a chest-strap heart-rate monitor that broadcasts in ANT+ (to allow it to work with the CORE), and a device to allow me to see these data live. Suunto, Garmin, and Coros all permit this.

Obviously a running vest with appropriate amounts of water and salt, as well as food.

Method

Over the years, I have noticed that when my core temperature exceeds 38.8º, I lose the ability to maintain output. For running, I've noticed that at the hotter end of the range, I can maintain up to 155BPM. Much more than that, and my core temperature rises rapidly, performance decreases, and WARNING USER DEATH IMMINENT flashes on my HUD.

I watch my HR, and as it approaches 155, I reduce my pace. Sometimes this reduction is comically slow - what my partner calls 'holding running shape' - but the key thing is, I'm still running, unperturbed by the heat.

TL;DR

I go more slowly, running by my HR to not overheat. Water, salt, to feel, to taste.