Running Hot

I just got back from a midday run and it was HOT! (especially for a guy most used to running at 5:30 am). The heat of summer is here, and we must take precautions to avoid the dangers of excessive exercise in the heat. Excessive temperatures can impair performance and lead to dehydration and heat illness. Proper preparation and early recognition of heat illness will help us better enjoy our summer training.

Muscle action during exercise in our body’s main means of heat production. Only 25 percent of the energy produced by exercise is used for work or movement. The remainder of the energy is dissipated as heat. Some heat loss occurs directly to the environment when the environmental temperature is less than our body temperature. In warmer conditions, sweating is our primary means of losing heat. As our temperature rises, blood is shunted to the skin so that the heat may be lost through sweating. If heat loss does not compensate for the heat produced by muscle activity, body temperature rises. This is especially true if we allow ourselves to become dehydrated or in humid conditions where sweat loss is limited.

Heat illness can be graded as mild, moderate, and severe. Mild heat illness is termed heat fatigue and is characterized by tiredness and weakness, sometimes associated with a headache. Heat fatigue is generally responds quickly to cessation of activity and drinking fluids. Heat cramps may occur and are treated with rest, icing, stretching, massage and rehydration.

Moderate heat illness is termed heat exhaustion. Weakness and fatigue are more prominent. Other symptoms include dizziness, nausea, and even mild confusion. Treatment mandates cessation of activity, getting out of the heat, rapid cooling, and rehydration.

Severe heat illness is termed heat stroke and is a medical emergency. The runner now has an impaired level of consciousness which differentiates this more serious form of heat illness from heat exhaustion. The athlete with severe heat illness may actually have hot dry skin rather that be sweating. Immediate cooling and formal medical assistance is needed to treat heat stroke.

Heat illness can often be prevented by following some basic guidelines:

Acclimatization: If you are not accustomed to running in hot weather, gradually introduce time in hotter, humid conditions to your training. Otherwise, try to avoid the hotter periods of the day. Train early in the morning or later in the evening. Consider taking it indoors to the treadmill if it is especially hot.

Wear loose-fitting, light-colored clothing that allows moisture and heat to be lost from the body.

Proper hydration: In addition to fluids needed for daily maintenance, athletes need to replace fluids lost with exercise. Drink 2 cups of fluid 2 hours prior to exercise. Drink roughly one cup of fluid for every 20 minutes of exercise. If exercise is less than one hour, water is adequate. If exercise exceeds one hour, a sports drink will replace sugar and salt in addition to fluids. Not all of this needs to be done during exercise, but that not consumed during exercise should be replaced within a couple hours of training. Another method of monitoring fluid needs is to weigh yourself (unclothed) before and after exercise. Drink 2 cups of fluid for each pound lost during exercise. Now don’t overdo it either. Some folks adhere to the “more is better” theory. Drinking excessively, especially excessive amounts of water, can lead to hyponatremia (low salt) which can be potentially dangerous. So stick to the above guidelines and things should be fine. Also avoid alcohol and caffeine which can also promote dehydration.

Treat heat illness early. If you or a teammate experiences the signs of heat illness, stop running. Move indoors or to the shade. DRINK. Cool towels soaked in ice water can be draped over the athlete to more rapidly cool if necessary. Rapid cooling and medical attention are needed in all cases of severe heat illness.

And don’t forget about your skin. Sunblock to exposed skin to prevent sunburn!

Enjoy the summer!

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2 thoughts on “Running Hot

  1. Cris

    Hi, and great blog — I’ve added to my reading list.

    A question — have you noted that different athletes have different tolerances to heat and humidity? I’m a female long distance runner, and I’ve found that I’m a completely different runner in the summer and winter, even as compared to others.

    I train with a team of runners of different abilities, and I’ve found that I’m affected enough by the conditions that I have to drop from my normal group into a slower group on hot weather days (especially if it’s humid or bright sunshine) — basically I slow down by much more than my training partners. And conversely, on days where the temperatures dip below 40, I’m way ahead of them.

    How much individual variability is there in how athletes handle heat?

    Reply
    1. University of Virginia Center for Endurance Sport Post author

      Hi – there is a post on this blog as well about heat and humidity. In general, it takes 2 weeks to acclimate to hotter climates. To answer your question, some folks do better with heat than others. A lot of factors constrain this – sweat rate, muscle mass, hypothalmaus function, parasympathetic nervous system function…..lots of things.

      I read a study that showed runners begin to have a decline in max performance around 74 degrees – not to say that you can’t run over this temp, just said things become impaired due to weather at that level.

      Reply

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