When doing any vigorous physical activity in hot or humid weather, especially if you are not used to exercise, you risk heat illness, including heat exhaustion and heatstroke. Your body produces heat when you exercise vigorously, and that heat can combine with the outside heat to reach dangerous body temperatures. High humidity prevents your body from cooling itself through the evaporation of sweat because the sweat does not evaporate as easily or as quickly in humid air. You will need to drink more water in hot, humid weather to cool your body.
If the air temperature is less than 80 F, you can be active outside without taking any extra precautions. As you exercise:
Drink water periodically, such as a few ounces every 20 to 30 minutes.
Lower the intensity of your exercise if you are getting hot.
Find some shade if you are exercising outside.
When the temperature gets past 80 F, consider both the heat and the humidity. The hotter or more humid it is, the higher the risk of heat-related illness. For example, if the humidity is 60%:1
Be careful exercising in temperatures of 80 F to 85 F.
Experts advise being extremely careful between about 85 F and 90 F
The conditions are considered dangerous or extremely dangerous at temperatures over 90 F.
When the weather is hot or humid, or both, consider exercising early in the morning or in the evening, or in an air-conditioned area. You also have less chance of overheating if you choose less strenuous exercise. If you usually jog or run, try taking a walk on a shady sidewalk.
If you are a distance runner or a triathlete, there is a chance you could overhydrate during your training or event. Overhydration (hyponatremia) can be caused by exercising over a very long period of time, especially in hot or humid weather, and drinking too much fluid. It can cause symptoms such as nausea, confusion, and feeling bloated. Although it is rare, it is a medical emergency when it happens. An athletic trainer or sports nutritionist can help you learn ways to avoid overhydration.
It is important to listen to your body and get help from a health professional if you stop sweating or have other symptoms of heatstroke, such as confusion.
Source: Shannon Erstad, MBA/MPH
