Exercising and Competing in the Heat--Safe Summer Outdoor Workouts

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Sunlight acts as an insulating blanket by warming the skin.

Direct sunlight causes a rapid rise in body heat by elevating skin temperature—which should always be at least two degrees cooler than your core temperature to allow for a cooling heat gradient.

Your workout intensity and the length of your workout contribute to stress produced by heat. We generate heat during exercise and the human body isn’t particularly efficient in this respect—75% of our expended energy is turned into heat. Thus the faster and longer we run or exercise, the higher the heat load placed on our body.

Our previous exposure to heat is also a major factor in determining our susceptibility or resistance to heat illness. This is called acclimatization. Through training we can partially, but never completely adapt our thermoregulatory mechanism. In addition, people respond differently to heat, so adjustments to exercising in heat should be made on an individual basis.

Thus heat will always be a limiting factor to our endurance performance. Unfortunately, each summer thousands of runners, triathletes and other outdoor exercisers discover this the hard way and for some, it’s a fatal experience.

Even fit athletes can only tolerate a narrow range of internal core temperatures. The good news is that a fit person can tolerate a higher core temperature than an inactive person, so heat problems usually arise when athletes are inadequately conditioned for a race or pushing beyond their limits.