Acclimating to Heat and Humidity Part I

When you think about racing in hot environments you may think of summer. While summer can certainly be hot in several locations, it's often fall and spring racing that brings more trouble because athletes are traveling to warmer environments for events.

Whether you travel for racing or not, you may find yourself concerned with acclimation to heat and humidity. Consider the following situations:

  • You train in cool fall air and your next race is in a hot environment.
  • You train in cool spring air and the first race of the season is in a hot city.
  • You live in a city that is always cool relative to the locations where you race.
  • You live in a hot, dry environment but plan to travel to a hot, humid environment for a race.
  • You live and work in an air conditioned environment but race in a hot and humid environment.  

Most, if not all, endurance athletes have encountered the negative effects of heat on race results. Why is it that some athletes seem to handle hot conditions better than others and can anything be done to help you train for the heat?

Body Temperature

Your body regulates internal temperature within a relatively narrow range. Most people consider a normal oral temperature to be 98.6 degrees Fahrenheit, though there can be normal variations of 1 degree or more.

When internal temperature rises, your body works to cool down. At low levels of heat stress, your body is able to manage the load. As the heat load increases, you are at risk for heat cramps, heat exhaustion and the most serious condition of heat stroke.

Heat stroke occurs when your core temperature exceeds 105 degrees Fahrenheit. If not addressed, heat stroke can result in death.

Body Cooling

Your body regulates temperature through radiation, conduction, convection and evaporation. When your body is warmer than the environment, it radiates heat into the environment. Radiation does not require molecular contact between objects. The easiest way to experience radiant energy is when your body absorbs radiant energy from direct sunlight or reflection from snow, even in freezing conditions.

Conduction involves a transfer of energy from one molecule to another though a liquid, solid or gas. Conductive body cooling depends on the temperature difference between the skin and surrounding surfaces and the thermal qualities of those surfaces. For example, water is more conductive than air. You can sit motionless and comfortably much longer in a 75-degree-Fahrenheit room than you can in motionless water at the same temperature. This is because water has the ability to absorb heat several thousand times faster than air.

Convection is the heat exchange associated with moving air or water adjacent to the body. Back to the 75-degree example in the last paragraph, if you add a fan to move air past you while sitting in the room, you will feel cooler. If you are stationary in 75-degree water that is moving, you will feel much cooler than if the water was motionless.

The final, and most critical, body defense to overheating is evaporation. The evaporation of sweat from the surface of your body, the changing of a liquid to a gas, cools your skin. It is important to note that it is not sweat, per se, that cools your body; rather it is the evaporation of sweat from your skin that cools the body.

The relative humidity of the air surrounding your body is the most important factor that determines the effectiveness of evaporative cooling.

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