Surviving the Summer

By Susan S. Paul, MS; Track Shack Foundation Training Program Director

Welcome to summer running in Florida!  It’s hot, humid, and you want to run but, how can you train in this weather? Understanding how your body cools itself and functions in hot weather will help you survive the summer and even come out better for it! 

When we run, we get warm because our exercising muscles increase our body’s temperature. When body temperature rises, a greater percentage of blood flow is re-directed to our skin surface to carry away this internal heat which results in us breaking a sweat. Sweat is composed of plasma from our blood, which means that sweating heavily can decrease our blood volume.  Lower blood volume means less blood and that it becomes thicker which places additional stress on our heart because it must work harder to pump it; hence, the importance of adequate hydration in hot weather!  

Sweating doesn’t cool us down per se, but rather, it is the evaporation of that sweat from our skin that actually cools us off. As our sweat evaporates, we are cooled.  However, in Florida, we also have humidity and our summer weather means high temperatures and high humidity. Heat and humidity are a double-whammy.  Humidity refers to the level of water present in the air and, when humidity levels are high, it means the air is saturated with water. Under these conditions, our sweat simply cannot evaporate because the air is already saturated with moisture. Therefore, high humidity compromises our cooling system and makes us unable to cool off efficiently.

When our blood flow is redirected to the skin's surface for cooling purposes, it also means less blood is available to our exercising muscles. With less blood available, the heart is forced to work even harder to sustain our running, which results in a higher than usual heart rate.  Running at a higher heart rate means the run will not only feel harder but also, that you will go through your carbohydrate stores faster than usual.  You are also likely to accumulate a higher level of blood lactate due to the increased intensity too. Simply put, hot, humid weather means our usual run pace becomes difficult to sustain.

But, it’s not all bad news!  Training in such adverse conditions can also improve our performance.  Adverse conditions force our bodies to make special adaptations which can result in a performance boost when the adverse conditions are removed. The adaptations our bodies make to training in the heat are somewhat akin to training at altitude.  A few of the physiological adaptations our bodies make to training in the heat are:  increased blood volume, increased stroke volume which means the heart is able to pump more blood with each beat, increased plasma volume, a lower resting heart rate, increased myoglobin content which improves the muscles’ ability to use oxygen, a higher lactate threshold level which means the body can tolerate more lactate, and an increased number of red blood cells which means better oxygen transport.  All fantastic adaptations!  When the heat and humidity finally drop, we feel like we have rocket boosters on!  

This means when we get a break in our weather, or you travel up north for a race, all your training in the heat and humidity will pay off. But, for now, remember to be patient with your training and give your body time to make these heat adaptations. It takes the body a minimum of 6 weeks to make some of these adaptations, so in the meantime, slow down your run pace, drink lots of water, stay consistent with your training, and you will reap the benefits of running through Florida’s summer weather. 

Here are a few tips to help you get through the coming months:

1. Run at the coolest time of day, which is usually just before sunrise. Avoid running at the hottest time of day. 

2. Hydration is essential. Consume adequate amounts of water and sports drink with electrolytes before, during, and after a run. Plan shady routes and/or routes with water fountains.

3. Wear loose fitting, light-colored, tech clothing that wicks away sweat and dries quickly.

4. SLOW DOWN!  Slow your run pace down to adjust for the stress of training in the heat and humidity. 

5. Run by feel or Perceived Exertion Level rather than pace. Remember, if a run feels hard, it is hard regardless of actual pace. 

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