How To Use A Heat Index Chart

    Published: 06-16-2009
    Views: 10,198
    Registered Dietitian Roxanne Moore of Sodexo discuses the basics of sports nutrition, including how to use a heat index chart.

    Roxanne E Moore: Hi! I am Roxanne Moore, Registered Dietitian and Director of Wellness for Sodexo Schools. While you can practice good hydration throughout the week and during activity, there are environmental conditions that can challenge even the best of well hydrated athletes.

    Athletes should take extra care to monitor the heat index to avoid unnecessary stress and harm while exercising. The national oceanic and atmospheric administrations heat alert procedures are based mainly on heat index values.

    The heat index, sometimes referred to as the apparent temperature is given in degrees Fahrenheit. The heat index is a measure of how hot it really feels when relative humidity is factored in with the actual air temperature.

    The heat index chart provides general guidelines for assessing the potential severity of heat stress. Individual reactions to heat vary. So it should be remembered that heat illness can occur at lower temperatures than indicated on a chart.

    In addition, studies have indicated the susceptibility to heat illness tends to increase with age. Now here is how to use the heat index chart. First you want to read across the top of the chart and locate the environmental temperature.

    Down the left side of the chart you want to locate the relative humidity. Follow across and down to find the apparent temperature. The apparent temperature is the combined index of heat plus humidity. It's an index of the body sensation of heat caused by the temperature and humidity combined.

    As an example, if the air temperature is 96 degrees Fahrenheit and the relative humidity is 65%, the heat index or how hot it really feels is about 121 degrees Fahrenheit. The weather service will initiate alert procedures when he index is expected to exceed 105 to about 110 degrees Fahrenheit for at least two consecutive days.

    Since heat index values were devised for shady, light wind conditions, exposure to full sunshine can increase heat index values by up to 15 degrees Fahrenheit. Also, strong winds particularly with very hot dry air can be extremely hazardous for athletes.

    The heat index chart shaded zone above a 105 degrees Fahrenheit shows a level that may cause increasingly severe heat disorders with continued exposure of physical activity.

    Being aware of the heat index, coupled with daily good hydration and selection of the right beverage to help you replenish before, during and after activity is critical for athletic success.

    But one core principle of proper hydration is essential to remember, practice makes perfect, so experiment with various hydration strategies to learn what works best for you. Try different water and sports drinks in varying amounts and hydrate at different times during your workout to discover your optimal mix.