On a hot day we may feel like were melting, but did you know that our internal temperature (or core temperature) only changes by a few degrees. Our normal body temperature at rest is maintained between 36 and 38 degrees Celsius. Our core temperature is extremely important as the processes that occur in our cells need it to be very constant in order to keep the body alive. In fact, you will require medical intervention if it drops below 34.4 degrees, or above 41 degrees.


Sources of heat
Apart from the obvious source of heat: the environment, the body also has another major contributor: metabolic processes. Anything that increases energy production, the release of hormones, or basal metabolic rate, also increases heat production.


Body temperature whilst exercising
Body temperature reflects the balance between heat production and heat loss. As we exercise we increase our body temperature and for us to be able to continue we must be able to release the excess heat.

This is done using the circulatory system. The heat is carried by the blood, to the skin. It is then released into the external environment.

The release of heat is completed by any of 4 mechanisms:

• Conduction: the heat is transferred through contact with another object. This object must have a lower temperature. The body loses only small amounts of heat due to this process.
  
• Convection: the heat is transferred by the motion of a gas or liquid (eg, air across the skin when running, or water across the skin when swimming). As these air or water molecules come into contact with the body, heat is released to them, they move on, and are replaced by cooler molecules.
  
• Radiation: the heat is transferred from one object to another without contact. This can result in heat loss or heat gain, depending on the environmental conditions
  
• Evaporation: heat is transferred through the evaporation of bodily fluids when brought into contact with the external environment (eg, sweat evaporating off the skin, and to a lesser extent our breathe as we exhale). This is usually the most important form of heat loss during exercise. In this process the heat is transferred from the body, to water on the surface of the skin (sweat). When the sweat reaches a certain temperature it is converted to a gas and the heat is released into the environment.

• Expose as much of the skin as possible to the open air. This will not only allow the sweat on your skin to evaporate, but it will also allow some heat loss via convection.
  
• If you are not able to expose much skin (eg, sports uniform), then take frequent water breaks.
  
• Wear cotton clothing whenever possible.
  
• In extremely hot weather, take frequent rest periods.
  
• If you do not regularly exercise in hot conditions, take time to acclimatize before participating in high intensity exercise.

Ray Kelly

Ray has worked extensively in the health and fitness industry for over 15 years. He has a degree in Exercise Science and is a Level 2 Strength and Conditioning coach. Ray has been involved in athlete development for the Olympics and world championships for 10 years, also lecturing at coaching accreditation courses.