Running in the Heat – Surviving Florida Summers
By Hugh Thomas

After a nice cool winter this year, there can be few com- plaints from runners about recent running temperatures. but while the Florida winters can be variable, we all know that the summers are guaranteed to be hot and humid. so how can we better prepare for those steamy runs we know are in our future? First an abbreviated explanation of some of the physiology involved paraphrased from lore of running by Dr. tim noakes mD. the full version of this document contains some 80 pages on temperature regulation during Exercise for those of you who want to delve into the subject further.

As we exercise, our muscles produce heat when our stored energy is converted to mechanical energy. the body is not very efficient at this conversion and as much as 70% of the energy used in muscle contraction is released as heat rather than as energy to propel us forward. blood is heated as it passes through the muscles and distributes the added heat through- out the body particularly to the skin. at the skin, the heat can be carried away by air currents. surface heat is also lost when sweat evaporates.

As we increase exercise intensity, the body will direct blood flow to the muscles to assist with the added exertion in prefer- ence to increasing blood flow to the skin. the result is an increase in heat production and a decrease in the ability to lose that heat. controlling running intensity is a key factor in keeping body temperatures within limits. Humidity is a measure of the water content of the air. As humidity increases, the ability to lose heat by sweating decreases since the air around the skin cannot absorb additional water. In this case sweat does not vaporize, but rolls off the body without any cooling effect.

With sweating, fluid is removed from the body causing dehydration. Dehydration increases the heart rate and body temperature and reduces the heart’s output and stroke volume as well as blood flow to the skin and the exercising muscles all in proportion to the degree of dehydration. studies have shown that fluid intake does little to actually cool you down. However it will help to keep you going since it will keep your blood volume close to normal levels which in turn keeps your sweat rate high. since oxygen is delivered to the muscles through the blood, maintaining your blood volume through drinking, enables your heart to deliver more oxygen per contraction and perform better than if you allow your body to become too dehydrated.

Having reviewed a few basic concepts, let’s see what practical steps we can take to manage running in the heat. Here are a just a few suggestions I hope will help you in the coming months.


  • Keep your daily fluid intake up. take a drink bottle with you on the run. Plan your route to include shade and know where water is available, or run loops back to your home or car to replenish fluids.
  • Protect yourself from the sun with sunscreen, and a hat or visor. since the head is a major source of heat loss wear a mesh cap or even better, a visor, to allow heat to escape. wear light colored loose fitting clothing.
  • For the optimum body temperature prior to your run, con- sider drinking ice water while you take a cold shower this will help delay the inevitable rise in body temperature.
  • To assist with cooling try one of these techniques. Place a wet sponge on your head, put ice cubes on top, cover with cap. or, fold a bandana in diamond shape place ice cubes along the edge, roll it up and tie it around your neck. keeping the head and neck cool helps, because blood flow there is close to the surface of the skin
  • Pick your training time. run in the cooler hours, early a.m. or late afternoon. check the weather forecast for temperatures and cloud cover for the day. For long runs, an early morning start is usually more humid and will get warmer as you run. when my current triathlon schedule calls for a long run it is often the second workout of the day. starting the run in late afternoon is a little warm but as time goes by, temperatures gradually cool down making the last stages of the run much more tolerable especially when I am tired.

On the Walk/Run

  • Easing into your walk/run slowly on hot days will prolong the time before your body temperature reaches uncomfortable levels.
  • Running at a lower intensity is the most effective way to prevent your body from overheating. a lower intensity requires less muscle action and therefore less heat will be generated by working muscles.
  • Stay hydrated with regular fluid intake. water is fine up to 1 hour, after that a sports drink is preferable. If you use gels, essentially a concentrated drink, remember to take them with water for optimum absorption. taking gels with a sport drink increases the carbohydrate concentration resulting in slower absorption.


  • Gradually slow down at the end of your walk/run finishing at a comfortable/easy walking pace. This will allow you cool down as well as provide recovery for the legs.
  • After a long hot run I have found that relaxing in a pool while drinking iced water really works wonders in terms of reduc- ing body temperature, by cooling both the outside surface of the skin and the internal core. gently exercising your legs in the water which will help loosen them up too.
  • Drink ample fluids and watch for any dramatic weight loss which will be mostly lost fluid. Eat as your appetite returns.

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