Review of the Heat Index: an approach based on evidence

In the video linked below, you discuss thermal stress. Can you tell us a little bit about what this term means and what happens to the human body when it can no longer offset the increase in temperatures?

People are not very effective when we exercise, so we produce a lot of heat from muscle contraction. When the environment is hot, we can earn additional heat or we cannot lose body heat if the humidity is high (the least sweat evaporates). In many combinations of high temperature and humidity, we are able to balance heat production and gain with heat loss and the temperature of the core remains relatively stable (“thermal stress compensation”). However, above these environmental boundaries, the core temperature will continue to increase (“non -compensated thermal stress”) and the exercise will be limited. If this condition is prolonged, the risk of thermal illness increases.

You also explain the deficiencies of the heat index and the need for a better system with real -time warnings based on how heat affects health. What do you think it will look like and how soon this system could be available?

The heat index was designed by the National Meteorological Service to give a number for how hot it feels when the humidity is added to the temperature. The keyword is “feels”. This may not be a measure of the actual effect of heat on the human body. The heat index does a good job in assessing the impact of thermal stress on young, healthy men and women at rest. The relationship between the perception of the environment and its real impact is naturally collapsing, however, when we begin to exercise or for more vulnerable populations such as the elderly.

A measure that combines the effect of heat and moisture (and solar radiation from sunlight, also) on the body is the temperature of the wet volley (WBGT). WBGT is used by organizations such as military, industrial and sporting events to monitor thermal stress and take appropriate actions to protect participants.

How can health coaches and exercise professionals better serve their customers when it comes to training them for the dangers of thermal stress, especially when leading to outdoor exercise sessions during the summer months?

Education is the key. Important issues to discuss with customers before outdoor exercise in the hot summer months include the importance of heat acclimatization (slowly creating tolerance for heat exercise), hydration and recognizing the signs and symptoms of thermal disease.

Check out the following article, which has a CBS news video on Dr. Kenney, to find out more about thermal stress and efforts to develop a better warning system based on evidence and focuses on practical guidance on what elderly and other vulnerable populations can do to better protect themselves from heat.