Metabolism: the engine that heats your body
We are a furnace constantly producing heat: digesting food and producing energy to make our organs function and activate our muscles for movement. When it is cold, this helps regulate our body temperature. In hot environments, we don't have very good ways of cooling off. When you work out, the harder you work, the more heat you produce. If your body temperature gets too high (> about 39 degrees Celsius), that becomes dangerous. Let’s look at how we get rid of excess heat.
Our body has 3 main ways of maintaining a normal body temperature of approximately 37 degrees Celsius and eliminating heat: sweating, radiation, and contact with cold items, surfaces or liquids.
1. Evaporation by sweating: the most effective method, but also the most problematic. Loss of heat takes place by loss of liquid, which leads to dehydration if the loss is too significant. Some people sweat more than others and may lose up to 3 liters per hour. If there is high humidity (somewhat rare in Switzerland), evaporation does not work as well and heat builds up.
2. Radiation: the body radiates heat; this is what you feel when you are in a stuffy room with other people. But when you are working out, this is not very effective, and the opposite happens if it is hot: we receive heat by radiation from the sun or the ground.
3. Contact with cold, primarily circulating air: the faster the air moves, the more significant the heat exchange will be. There are 2 solutions: either you can move very fast to “create” wind against your skin (like when riding a bike) or there is natural wind, which allows heat loss to occur. You can also touch very cold objects (for example, a bottle of ice water in your hand) and heat loss will take place from the body to the bottle.
What dangers are there for your body?
Dehydration increases heart rate because the heart is trying to circulate the remaining blood more rapidly. Blood pressure may begin to lower and you may start to feel faint. In addition, the brain has a hard time with temperatures above 39 degrees Celsius. You are familiar with this if you have had a bad flu with fever. In addition to the discomfort, the brain does not function as well, slows down and, in extreme cases, it becomes difficult to control one’s body, as happened to Gaby Schiess-Andersen at the 1984 Los Angeles Olympics, and more recently to Jonathan Brownlee.
This situation becomes critical and the body may suffer a heatstroke, with potentially serious consequences. The signs you should be aware of are thirst, nausea or headaches, buzzing in the ears, and a sense of disconnection from others. All this seems worrying, but we will look at what actions to take to avoid these complications, which should remain rare and exceptional.
Golden rule: prepare and adapt
The body is a fantastic machine with a great capacity to adapt. At the start of the summer, you don't tolerate heat as well, but by working out repeatedly in the heat, you become more efficient at getting rid of heat. This is called acclimation. Within 10 to 14 days of heat and 2 or 3 sessions of moderate exercise, the process is already efficient. You can also use methods of passive exposure to heat, such as immersion in hot water or a sauna, to stimulate the body to adapt physiologically: improved capacity to sweat, better tolerance of increased body temperature, increased plasma volume and better cellular hydration management.
In practice, you can apply the following principles:
1. Moderate effort in high temperature and humidity for 60 to 90 minutes, going at a fairly slow pace, for a perceived maximum effort of 4 on the Borg 1-10 scale.
2. Immersion in a hot bath about 40°C for 30-45 minutes or a sauna for up to 30 minutes.
There are also other methods of physiological stress that allow your body to adapt, particularly hypoxic exposure and training, or exposure to cold (cryotherapy). At this time, it is not clear whether adaptations induced by these methods also improve heat tolerance, but we will find out in time. One principle remains true: stimulating the body with new sensations in a progressive and varied manner leads to positive adaptations; that is the fundamental principle of training.
ITU developed an excellent document called “Beat the Heat” this year, with good scientific data and practical advice for triathlons. It’s a good resource for those who want to know more.
In conclusion
Heat limits performance capacity in endurance sports, with reductions in the realm of 10% to 20%, and leads to risks of fainting, which are potentially hazardous to one’s health. Training in hot conditions while taking steps to adapt progressively works very well and should be pursued. In addition, it is worth the trouble to follow a few simple rules:
1. Slow down (or start off more slowly)! The harder you work, the more heat you produce. By taking it easy, you allow your body’s cooling mechanisms to work and they do not get overwhelmed.
2. Don't start off dehydrated and drink water, cool water if possible, if you are moving for over 30 minutes.
3. Dress in light colors (black absorbs more heat by radiation) and wear a cap.
4. If you pass by a water fountain, take a short break to spray your face and head with plenty of water and completely soak your cap.
5. Don’t pay too much attention to the data on your watch. Performance is often suboptimal and heart rate is higher at the same speed. Slow down!
Happy training!