Heat and performance

Body temperature regulation mechanisms

When our body uses carbohydrates or fats as an energy source for running or riding, the efficiency is only 25%, which means that 75% of the energy is converted into heat! To avoid overheating, the body therefore needs to evacuate this heat: the set of mechanisms that control body temperature is called thermoregulation.

Excess heat is eliminated by evacuating it from the inside to the outside of the body. As this heat is mainly contained in the blood, it is redirected to the surface (to the skin). There are then several processes that allow heat exchange with the surrounding air.

1. Radiation: It corresponds to the heat emitted in the form of infrared radiation.
2. Convection: It corresponds to the heat exchange with the circulating air.
3. Conduction: It corresponds to the exchange of heat between two objects touching each other.
4. Evaporation: It corresponds to heat loss through water loss (breathing, perspiration).

Why it's harder to run or ride when it's hot...

The mechanisms of radiation, convection and conduction depend mainly on the temperature difference between the body (about 36-37°C at rest) and the outside. The greater the difference, the more efficient these mechanisms are. On the contrary, when it is hot, the temperature difference between the air and the body decreases, which reduces the evacuation of heat by these mechanisms. Above 36°C, the relationship is even reversed: it is the body that receives heat!

The heat is then mainly evacuated by perspiration. The body adapts and has about 1 to 2.5 L of water that can be lost per hour! However, when the air is humid, the air is less quick to accept more moisture, so the evacuation of heat is reduced. A hot and humid environment is therefore particularly dangerous to any effort.

Decreased performance with heat

You have certainly already experienced it, running in hot weather is difficult, the sensations are not as goodand the performance is reduced. The graph below from a study by Ely et al. (2007) shows the drop in performance as a function of the time taken to run a marathon in different weather conditions. The WBGT index does not correspond directly to the temperature but integrates several parameters such as temperature of course, but also humidity, solar radiation, or wind. The higher the WBGT index, the more difficult the conditions are.

Impact of heat on running performance. The higher the WBGT index, the more difficult the weather conditions. It is noticeable that the best marathon runners (around 130 min) are affected minimally by heat. On the contrary, a runner in 3 hours can see his performance reduced by more than 10% in difficult conditions. According to Ely et al (2007).

Effects of compression sleeves on thermoregulation

Although compression sleeves or socks are widely adopted by sportsmen and women when the outside temperatures are cool, their use remains moderate in case of strong heat. Wrong?...Surely! Explanations ...

Evolution of the skin temperature measured on the calf of a cyclist with and without compression sleeves (dry or wet).

The graph on the left shows that the skin temperature of the calves is slightly higher (+2 °C) when a cyclist is equipped with Compressport R2V2 sleeves than when he or she is not wearing them. However, the graph on the right clearly shows that when the same rider is splashed with water, the calf temperature is much lower with the sleeves than without (-5 °C). This is a conduction phenomenon which, as mentioned above, corresponds to the exchange of heat between two objects that touch each other, the heat going from the hottest object (the skin) to the coldest (the sleeves).

Compressport products specificities to deal with the heat

The majority of Compressport products are designed to be worn in extreme conditions, as can be the case during the Ironman World Championships in Kona or during the Diagonale des Fous on Reunion Island.

For this we attach great importance to protection against ultraviolet rays (UV) for example. All areas directly exposed to the sun are guaranteed by a UPF marking (for Ultraviolet Protection Factor) similar to sun creams (ranging from 15 to 50+).

Emphasis is also placed on lightness. The aim is to create a clever mix of specific meshes. The most exposed areas are slightly thicker to provide UV protection and refresh by retaining water while other areas are much lighter to provide maximum ventilation and performance.

Practical applications and conclusion

The hotter and more humid the environment, the more you will see your performance drop (up to 5-10%)! To cope with the heat, you should therefore opt for technical clothing: light in some places and thicker in others. That's what we strive to do ... because performance is our priority!