Exercising in the Heat: How to Stay Safe

Summer exercise opportunities are endless but they can also be dangerous if you're not careful about exercising in the heat.  How hot is too hot?  That depends on your individual ability to tolerate heat and whether or not you use a little common sense.

What happens when you exercise in the heat?  Hot weather and bright sunshine increase our body's thermal load. The hotter we get, the harder we have to work to keep our body at a safe temperature.  We do that by increasing our heart rate approximately 10 beats per minute for every degree our body temperature rises.  We also shunt blood to our body's surface so it can be cooled through our natural air conditioning system - our skin and good old sweat.  When we perspire, heat evaporates along with our sweat, cooling the blood that's close to the surface.  But while this natural cooling system works well most of the time, it can add a major workload to our heart when the heat is really on. 

What happens when we get too hot?  Heat exhaustion and heat stroke are two major, dangerous and potentially fatal heat-related illnesses.  Our bodies can only survive core body temperatures greater than 106F for a short period of time.  At 114 degrees, body protein breaks down.  If we can't cool ourselves off, body organs quit functioning. People can feel the effects of too much heat at much lower body temperatures and develop heat-related complications.  Warning signs that it's getting too hot to handle are:

  • Profuse sweating
  • Pale skin
  • Muscle or stomach cramps
  • Fatigue
  • Weakness
  • Dizziness
  • Headache
  • Nausea or vomiting
  • Fainting
  • Rapid and/or weak pulse

Don't let a little heat keep you out of the game though.  With a little planning you can exercise in the heat safely.

  • Stay fit year round with regular exercise.
  • Choose the coolest time of day (early morning or evening) to work out. If the temperature is above 80° F and the humidity above 80%, postpone your outside workout until things cool off.
  • Ditch the spandex and heavy exercise clothing for lightweight, light colored, loose fabrics that allow air circulation and let perspiration evaporate. 
  • Monitor your heart rate and make sure you're not working too hard. 
  • Choose an easier route, routine or program on the hottest days to avoid taxing your cardiac system too much. 
  • Hydrate, hydrate, hydrate -Drink lots of water before, during and after you exercise:
  • 8 - 12 oz. of water 20 - 30 minutes prior to exercise plus
  • 6 -10 oz. additional every 30 minutes your exercise.


If you're exercising longer than an hour, you might need a sport drink to replace electrolytes and sugar.

If you start feeling overheated, stop exercising, find a cool shady spot and cool off.  If you develop any of the signs of heat exhaustion, call 911.




Exercise and the Heat

By: Dr. Gordon Blackburn (Director of Cardiac Rehabilitation, Preventive Cardiology and Rehabilitation Program)

Cleveland Clinic



Exercise in the Heat

By Timothy Noakes

Clinical Sports Medicine