Acclimating to Heat and Humidity Part II

In Part I of this two-part column, you learned how the body cools itself and what the risk factors are for heat illness. In this column we will explore strategies to reduce or prevent the affects of heat and humidity on your training and racing.

Heat Slows Pace

At the U.S. Olympic Training Center Heat and Humidity Conference, Georgia State University's Laboratory for Elite Athlete Performance director, Dr. David E. Martin, noted that the body enjoys a very tight range of temperature control. From a resting average baseline temperature of 98.6 degrees Fahrenheit, our bodily enzymes function optimally during exercise at a temperature of 102.2 degrees Fahrenheit--this is one reason why we should include a warm-up prior to vigorous exercise.

A mere 2.8-degree increase in core temperature from optimal performance temperature places us near our thermal death point.

The most serious form of heat illness, heat stroke, is defined by a body core temperature greater than 105 degrees Fahrenheit. A mere 2.8-degree increase in core temperature from optimal places us near our thermal death point.

Because high intensity exercise contributes to increasing core temperature, pace must decrease when environmental temperatures increase in order to avoid heat illness. Dr. Martin estimates that overall marathon run time increases approximately one minute for every 7 degrees Fahrenheit above 54 degrees.

Jeff Galloway agrees that heat slows pace. He estimates the affects of heat on pace by assigning a percentage increase to various temperature ranges. In his example, he estimates that if you are an 8-minute-per-mile runner your pace will slow according to this chart:

55-60 degrees: 1% - 8:05
60-65 degrees: 3% - 8:15
65-70 degrees: 5% - 8:25
70-75 degrees: 7% - 8:35
75-80 degrees: 12% - 8:58
80-85 degrees: 20% - 9:35
Above 85 degrees: Forget it... run for fun

Interestingly, at least one study showed that warm weather has a greater negative impact on faster runners than slower runners. The study concluded that the slower running velocities from start to finish caused less pace degradation. This is likely due to the fact that higher paces require higher rates of cooling to keep the body out of the heat danger zone.

What Causes the Body to Gain Heat?

Certainly ambient temperature, relative humidity and exercise rate are factors that can cause your body temperature to increase. Part I included a partial list of risk factors for heat illness. Other factors that influence body temperature regulation and can contribute to heat illness include:

  • Basal metabolic rate (BMR)
  • Hormones
  • The thermic effect of consumed food
  • Age
  • Gender
  • Percentage of body fat
  • Level of heat acclimatization

You Can Improve Heat Acclimatization

Unfortunately, there are several items that you cannot control, which affect your ability to tolerate hot environments. The good news is that you can influence your level of heat acclimatization and improve your ability to tolerate heat in both exercising and non-exercising conditions.

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