Exercising in the heat: what to know before you start

June 11, 2017

Ambient temperature impacts your body's response to exercise. Here are a few important considerations when exercising in high-heat.

As humidity and temperature increase, your risk of heat exhaustion and heat stroke increase.

San Jose's average relative humidity is between 60-80%. That means risk for heat exhaustion starts when temps reach 90° and risk for heat stroke when temps reach 100°.

To reduce your risk during hot months, exercise in the morning or evening when temps are lower and be sure to give yourself plenty of rest while exercising.

Dehydration is a product of losing fluids during exercise and not replacing them.

This is compounded with high-heat because more sweat evaporates, and high temperatures increase your rate of perspiration.

Researchers recommend drinking 500-600 mL of water before exercise, 200-300 mL every 10-20 minutes during exercise, and 450-675 mL for every half-kg in body weight lost (that's about 1 liter for every pound lost).

Knowing the signs of heat exhaustion and heat stroke can help you prevent serious injury.

Heat exhaustion is characterized by a weak but rapid pulse, low blood pressure, fatigue, headache, dizziness, general weakness, paleness, cold and clammy skin, profuse sweating, and/or body temp above 104°. Heat stroke is more serious and is characterized by hot and dry skin, bright red skin color, rapid and strong pulse, irritability, aggressiveness, anxiety, labored breathing, and/or body temp above 105°.

Someone with heat exhaustion should stop exercising, move to a cool and well-ventilated area, lay down and elevate feet 12-18 inches, drink fluids, and monitor body temp.

Someone with heat stroke should have emergency medical services contacted immediately and stop exercising, remove as much clothing as possible, use ice or wet towels or fans to cool the body, drink fluids, and get taken to the emergency room.

In good health,


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