At What Point Should Summer Heat Cause You to Stay Indoors to Train?

running with water
Runners compete in the 2013 Marine Corps Marathon Forward at Camp Leatherneck, Afghanistan Oct. 27, 2013. (Photo by Sgt. Bobby J. Yarbrough)

Most of us are not used to working out in the irregular heat patterns of the summer, when temperatures can change by 10 to 20 degrees in a short period. Though it is always important to mind your hydration and electrolyte levels when training in hot, humid or arid environments, there is a point when it is safer to stay indoors and train.

Yes, it is wise to acclimate to the heat (as well as the cold), but when the temperature changes are steeper than usual, you should consider moving your training indoors or at least to pre-dawn hours when the day is at its coolest.

Another option when temperatures are breaking records and are 10 to 20 degrees Fahrenheit higher than normal is to avoid midafternoon workouts in the sun. Wooded trails may offer some shade and relief from direct heat, but you should still be careful since humidity can cause profuse sweating and make you a heat casualty if you do not consistently rehydrate every 10 to 15 minutes.

If you are going to train in high temperatures, make sure you are careful to bring extra water, either in bottles or in backpack form. Increased electrolytes are an absolute must in these situations, so make sure sodium, potassium and magnesium are added in the form of powders placed in water bottles or in the food you eat before and after exercise.

Consider staying close to home or a populated area versus running in the wilderness. If you do decide to run a few miles away from home, strategically drop a few water bottles along the route so on the return, when you need the water and electrolytes the most, you have it on those last few miles of the running path.

Watch out for air quality. In some locations, when the heat and humidity trap pollutants from nearby metropolitan areas, running in the heat of the day can be as bad for your lungs as smoking cigarettes. From the problems created by forest fires to pollutants trapped in heavy air, avoiding strenuous breathing activity outdoors is just plain smart. Go inside and skip outdoor running in this situation.

Take a swim. If you did not get your workout done before sunrise, consider using an indoor gym for the prescribed calisthenics and cardio or lifting. Follow up any hot workout with a dip in the pool for an immediate cooldown effect. In fact, after a hot and exhaustive workout, a 10-minute tread in a cool pool or body of water can revive you, as much of your fatigue is due to body heat in the first place. Regardless of your conditioning level, having a cool water option like a pool or hose to drench yourself can be a lifeline when having to endure the heat for longer periods of time.

Don’t be a heat casualty. Only a few hours without water can undo all the training you put in over many months or years to get to where you are now. Heat casualties can occur in military and athletic summer training during long rucks or runs, outdoor PT, or merely during general training on a hot day.

The same can happen to young athletes at practice or preseason workouts, sports tournaments or summer camps. Anyone who’s doing manual labor, yardwork or other outdoor chores can quickly suffer the same fate, especially if they are not hydrating enough before and during these activities.

The confident exerciser is the one most in danger in these situations, since they may try to tough it out and find themselves in the hurt locker quicker than they could have ever guessed. Keep a record of the daily workout temperatures as you slowly acclimate from the spring months into the summer.

When you see a temperature that is 10 to 15 degrees (F) higher than normal, you should consider changing the time of day that you train or staying indoors, especially as you reach 100+ degree heat.

As with any exercise, you need to progress logically as you acclimate yourself to increased temperatures over time. The last thing you want is to go from working out in an air-conditioned gym all spring into the summer heat without any transition time.

If you stay hydrated and sip throughout the day, add electrolytes (salts) to drinks and food, find shady places to cool yourself, go to the pool for a few minutes, wear light or white clothing, and take frequent breaks, you can endure long days of activity outdoors in the heat of the summer.

Stew Smith is a former Navy SEAL and fitness author certified as a Strength and Conditioning Specialist (CSCS) with the National Strength and Conditioning Association. Visit his Fitness eBook store if you’re looking to start a workout program to create a healthy lifestyle. Send your fitness questions to

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