Thermoregulation for Triathlon. What you wear IS important!

Thermoregulation for Triathlon. What you wear IS important!

Last year I was racing in the Cairns 70.3 triathlon. The Pro field had some great names; Jacobs, McKenzie, Rix, Berkel… the list goes on. The swim was quick, the bike even quicker. After loosing a bit of time to the leaders in the swim, I preceded to “smash” the bike and try and make up for lost time. By 60km I had caught all but four athletes, and by the end of the bike I had caught McKenzie and Appleton, which only left Jacobs and Rix – but they were long gone! I was tired, but my ego was driving me. I started the 21.1km run at 3.15min/km pace. I could see Josh Rix, I was thinking ahead, I was… I was gone! Reduced to walking and an incoherent mess, I quietly found myself the shade of a tree at roughly the 8km mark. Race over. I walked to the finish.

Anyone that has had the pleasure to go to Cairns, not necessarily for a triathlon, will vouch that it has spectacular rolling scenery but is pretty much an oven with high humidity and high temperature. The moment you step off the plane you are hot and moist, and then add in any physical activity and you resemble Robbie Williams mid-concert (stick with me here). Therefore a triathlon in these conditions, let alone a long course triathlon, places a large stress on our in-built cooling system or our ability to thermoregulate. Any failure in thermoregulation, whether it is going above your physical capacity, failing to restore fluids, electrolytes, or energy supplies, or wearing too much insulative clothing, will cause the body to shutdown and go into “conservation mode”. That’s exactly what happened to me. So let’s try and make sure you avoid the same fate.


Thermoregulation is the process in which heat exchange occurs between the skin and the environment, or visa versa in hot conditions. To understand this process further, we have to look at the individual components that make up this process. The amount of heat in the body (storage) can be expressed through this equation:

Storage = Heat production – Heat Loss

Heat production is the difference between our baseline metabolic rate and our metabolic rate during an activity (external work). Therefore the harder you work, the more above your “threshold” you go, the more heat you produce. This heat production has to be matched by heat loss, and this process is a little more complicated. Heat loss is the sum of heat exchange via conduction, radiation, convection, evaporation, and respiration. The simple equation above can be expanded into a slightly more detailed one below:

Storage = (Metabolic Rate – External Work) – (Conduction + Radiation + Convection + Evaporation + Respiration)

Lets have a look at the components of heat loss a little further.

Conduction – heat transfer when in contact with an object (water, ground, etc)

  • Radiation – heat transfer from the sun or reflected off objects nearby
  • Convection – heat transfer from movement of liquid or gas (airflow around skin)
  • Evaporation – heat transfer through sweating
  • Respiration – heat transfer during normal respiration

And for those that prefer visual input, here is a schematic diagram of heat transfer during exercise.


As well as the components mentioned in the heat balance equation, there are a number of variables to thermoregulation that all triathletes will experience and have to deal with. I call these the “Enablers ”! You can either use these to your advantage or they can turn around and drive you into the ground. Metaphorically and literally.

Enablers to Thermoregulation

  • Air Temperature: An increase in air temperature will decrease the benefit of conduction, convection, radiation, and therefore increase reliance on evaporation. An increase in evaporation will obviously increase the need for adequate hydration and energy replenishment.
  • Air Humidity: Normally moisture concentration will be higher at skin than the environment, therefore causing rate of evaporation to be positive (i.e. skin to environment). In regions of high moisture concentration, not necessarily high relative humidity, this is reversed (environment to skin, -ve rate of evaporation). When 100% humidity is present, moisture concentration will be higher in higher temperatures as apposed to lower temperature.
  • Wind speed: Increase wind speed across skin will cause an increase in convective and evaporative heat losses. If win speed is minimal or non-existent, then visa versa.
  • Radiation: Minimising the amount of skin exposed to sun exposure will decrease the amount of heat transferred to the skin through radiation. More time in the shade, or the addition of reflective elements to clothing helps.
  • Clothing insulation: clothing acts as a barrier between the transfer of heat and moisture between skin and the environment.

Therefore with the heat exchange equation in mind and knowledge of the “enablers” to this equation, how do we best use it to improve our performance?

The trick is to use the “enablers” of heat exchange to our advantage and allow heat loss to occur as efficiently as possible. It is not possible to keep our metabolic rate at basal levels, or complete rest. Nor is it often possible to change the environment we perform in and to change the role of convection, conduction and radiation. The conditions are there for everyone to race in. Therefore the main area we can change and improve is the role of clothing. If we ensure that we have the best possible clothing that “enables” heat transfer to take place and reduce the insulation that comes from another layer on your skin, then we will see our performances improve as a result.

Here are some tips to ensure the clothing you are currently wearing is helping you beat the heat.

  • Thickness – You want a garment that is as thin as possible. Research has found that the thickness of a material is the most important factor in heat exchange. Obviously not so thin that it is opaque, but when you hold it up to the light you should be able to see light come through.
  • Materials and Construction – A 100 percent polyester garment will act like a piece of cling-wrap on your skin. A 100 percent cotton garment will absorb any drop of moisture attached to your skin, then not let it go making you feel like you are carrying around liters of water. The solution is to wear a garment with either a combination of polyester and cotton, or a polyester garment with enough pores to allow moisture transfer. Again, you should see the light if this is the case.
  • Hydrophilic versus Hydrophobic? You have seen the swimmers wear them, you may even own a “super-speed suit” yourself. These water-hating, or hydrophobic suits are quick in the water but are not so good for thermoregulation. So if you do races that allow wetsuits during the swim leg then go for a garment that is hydrophilic to aid in keeping your body cool.
  • Wear white – As most of you already know, the color white reflects more radiant heat than black. This is generalized and there are now black materials out there that also reflect light. But to be safe, use this general rule.
  • Finally, the garment should cool you down in the places needed the most! This is a topic deserved of a stand alone section. During exercise we are hotter and sweat more in different areas of our body. Regions that this is highest is the head, chest, back and underarm. So if during the run leg you are feeling constricted on the chest or have salt stains across your back, then you know that your garment is holding onto your sweat and not transferring it to the environment as best as possible. At Scody this is an area of great importance to us. The Research and Design Team is currently testing the most advanced and high-tech materials available and using heat and sweat zone mapping to make sure we are achieving optimal thermoregulation.

The subject of thermoregulation can be very complex and confusing. When you discuss it in relation to endurance sport it becomes even more complex and confusing. My advice to you would be simple. You sacrifice a lot and you expend so much energy on getting to the start line. Minimise the effect of heat by making sure you use a garment that will make you feel cool, comfortable, and fast!

John Polson

Doctor of Physiotherapy, Bachelor of Sports Science, Professional Triathlete


1 Comment

  1. adam
    May 9, 2013

    very good reading young man – I like it


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