Below is the Heat Index Chart from the National Oceanic and Atmospheric Administration (NOAA):
At temperature and humidity combinations below 80 degrees and 40 percent, there are no concerns. Notice that at a temperature of 88 degrees Fahrenheit and 40 percent humidity, the heat index remains at 88 and caution is needed. Keep the temperature at 88 and raise the relative humidity to 75 percent and you've got trouble. In this situation, the heat index soars to 103 and conditions become dangerous.
When the surrounding air contains high amounts of humidity, or water, the ability of the air to take on more liquid from your body is diminished or completely eliminated. Recall it is not the actual sweat that is cooling, it is the evaporative process.
Risk Factors for Heat Illness
Whether or not you will have problems racing in a hot and humid environment depends on many factors. Some of the environmental factors have already been discussed. Additional risk factors include:
- Low level of fitness
- Lack of heat acclimatization
- Individual ability to tolerate heat
- Glycogen depletion
- Current viral or bacterial illnesses
- Sleep deprivation
- Non-porous clothing that doesn't allow sweat evaporation
- Past history of heat illness
- Drugs (including alcohol) and medications (prescription and non-prescription)
Preparing for a Hot Race
If you anticipate racing in hot or hot and humid conditions, there are things you can do before the event to increase your chances for success. While you cannot change the environment, you can change things about your preparation that can increase your chances for a successful race. Those preparation strategies will be covered in Part II.