Houston Marathon Committee, Inc.

Hot weather running tips

Summer may be winding down in many parts of the country, but the weather is still hot and steamy in Houston. Training in hot, humid weather means you should pay extra attention to the conditions and how your body responds to them. Chevron Houston Marathon Medical Director John Cianca, MD, offers a few tips below to help you train in the heat.

Running in the Heat

It is really hot out. Not the best weather to enjoy a run in but if you’re going to run the Chevron Houston Marathon it is prime training time. I would like to give you some information to help you understand how to get the most out of your body and still remain safe and able to perform after your run is done.

Your body generates heat when its muscles are working. The harder they work the more heat you generate. You vent that heat by sweating. As the sweat evaporates it cools your body. If it is hot out it also makes your body hot in addition to the heat it is already generating. Worse, if it is humid, evaporation does not work so well so cooling via sweating is less effective. And as you know we live in a climate that is both hot and humid. Overheating is a real concern in our climate. The best way to reduce this risk is to reduce the intensity of exercise, exercise in the shade or indoors, and reduce the time of exercise sessions.

Hydration is a means to keep the fluid levels in your body to a level that is optimal for its function. Adequate fluid levels enable the sweating mechanism which will in turn help the body stay cool. Fluid in and of itself will not make you cooler. So the best way to immediately cool your self is to decrease activity intensity and move to a cooler area.

As you exercise you lose fluid and sodium (salt) from sweat, you need to replace these substances to allow your body to be able to function normally. Determining how much fluid to replace is an individual process since people sweat differently with respect to volume and content. Being under hydrated or over hydrated is not healthy and it will impair your performance. While drinking water is good for replenishing lost water, it does not address the sodium that was lost. This is why sports beverages were created.

The best way to estimate your needs is to use your body weight as a guide. Weight change during activity is almost entirely due to sweat loss. If you weigh yourself before activity and then immediately after (make sure to remove sweat soaked clothes), you can have a fairly accurate estimate of the amount of fluid that needs to be replaced. For every pound of weight lost, replace with 16 ounces of fluid, preferably fluid that has some sodium content. If you do not lose weight, don’t replace fluid other than for thirst. If you have gained weight, you should not consume fluid until you are urinating regularly. Weight gain during exercise implies fluid overload and this must be reduced before consuming more fluid.

For bouts of exercise less than an hour, you can safely and effectively rehydrate after the exercise is concluded. When you are exercising for longer than an hour, you should consider replacing fluid during exercise. You can estimate your sweat rate by using the weight lost during exercise in similar conditions, divided by the length of time exercising. For instance, if you lose 3 lbs in 2 hours of exercise in 75 degree, 85% humidity weather, your sweat rate would be 1.5 lbs (24ounces)/hour for those temperature conditions. You would then want to replace fluid at roughly this rate (24 ounces an hour) to maintain or restore your normal hydration level for similar conditions. As you become more fit, your sweat rate will change so you should continue to check your weight pre and post workouts to best understand how your body is reacting.

And in the category of TMI, the color of your urine also can be an indicator of your hydration status. Normal urine is pale yellow. If urine is dark, you are under hydrated. If it is clear, you are over hydrated. So now, you have two efficient ways to estimate your hydration status and to estimate your fluid needs. Nonetheless, be careful and conservative on hot days. Ultimately training is most effective when your body is challenged but not overwhelmed.

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