Effects of Heat on Exercise


It’s surprising that people are discouraged from exercising outdoors in hot weather but there is minimal advice given to people on exercising indoors where the conditions are frequently potentially more dangerous and debilitating. Try and find a fitness centre with fans to cool participants on the internet and you’ll begin to realise how the need for cooling is ignored.  In fact the myth is that the more you drip with sweat the better workout you’re getting. Whereas, in reality, the more you drip with sweat the more you’re wasting your time.

I’ ve put this section together as very few people are aware of how the body creates and gets ride of heat during exercise.


Why do we get hot and sweat?

If you’ve ever wondered why you get hot when you exercise it’s because about three quarters (75%) of the energy you use is given off as heat! So, if you’re creating 250 watts on your bike, another 750 watts will be created in heat. Stand in front a 1000w heater and you’ll get an idea of how much heat you have to get rid of if you’re not going to over heat.

When your body warms up two things happen:

  1. it increases blood flow to the skin to lose heat by convection
  2. you start sweating to lose heat by evaporation

The hotter your body gets the more it diverts blood to the skin and the more sweat it produces. Cycling outside on a hot day you’ve no doubt notices that when you stop you start dripping with sweat. This isn’t because you’ve started sweating, it’s the amount of sweat that has been produced evaporating off your skin when you were moving. A similar thing happens riding up a hill on a hot day and there is little wind you’ll notice that you’re dripping with sweat.  Indoor cycling in a warm room, without a fan, is like riding up a hill on a day without any wind.

Hyperthermia is the raising of the body temperature and is caused by:

  1. High exercise intensity
  2. High air temperature
  3. High relative humidity

Effects on performance:

  1. Reduces muscular endurance
  2. Shifts metabolism from aerobic to anaerobic causing a faster use of stored carbs in muscles and liver.
  3. Causes dilation of the blood vessels in the skin and pooling of blood in the limbs. This reduces the amount of blood returning to the heart and output and places more more strain on the system increasing the perceived exertion.

Combating Heat and Hyperthermia

  1. Heat Acclimatization.  Gradually get used to exercising in the heat.
  2. Clothing
  3. Air flow
  4. Exercise in a cool room

Day to day variations to heat tolerance

  1. Viral infections
  2. Sleep loss
  3. Low carbohydrate stores
  4. medications
  5. Sudden increase in training

Resources

Performing in Extreme Environments : L E Armstrong PhD

Spinning : Beat the Heat

Cleveland Clinic : Exercise and the Heat