Heat exchange during training

Heat exchange explains why the same workout feels easy in a cool gym but suddenly becomes hard in a hot, humid room. Your body tries to keep its temperature within a narrow range, but training puts extra demands on that process.

Your body temperature is maintained at 36.5 – 37.0 degrees C regardless of the temperature outside. This means heat production and heat loss must stay in balance. If either becomes too dominant, your body quickly lets you know.

Why heat exchange matters during training

Your muscles are not the only things working during a workout. Your body’s cooling system is working too. The greater the training load, the more heat you produce. If your body cannot release enough of it, you start to feel worse: your heart rate rises, movement becomes harder and you lose concentration.

For someone wearing light clothing, chemical thermoregulation, or heat production, and physical thermoregulation, or heat loss, are balanced at 18-20 degrees C. This is known as a comfortable temperature. In the gym, on the running track or during a competition, however, the situation can be very different.

Heat exchange is not just a hot-weather issue. Your body also has to respond effectively to the cold. When you train outdoors in winter, a damp wind can cool you down faster than dry cold. Meanwhile, your working muscles generate more heat. That makes your choice of clothing, warm-up and pace practical decisions, rather than simply a matter of comfort.

How heat exchange works in your body

Heat is released mainly through your skin. Your body does this through radiation, conduction and the evaporation of water. The most visible sign is sweat. As sweat evaporates from your skin, heat leaves your body. When sweat evaporates from the body’s surface, heat loss amounts to 0.58 kcal per 1 ml of water.

When you are hot, the blood vessels in your skin dilate. Blood flows closer to the skin, allowing heat to reach the body’s surface more easily. This is why your face turns red and your skin feels warm. It is a normal cooling response, not necessarily a sign of poor fitness.

Humid air makes things more difficult. When the air is saturated with water vapor, sweat does not evaporate readily from your skin. You can be soaking wet without your body cooling down enough. This happens in hot steam rooms, in subtropical and tropical climates, and sometimes in poorly ventilated training spaces.

So what actually happens? Heat loss slows down and hyperthermia, or overheating, develops. When body temperature rises above 38.5 – 39 degrees C, there is a risk of heatstroke. You need to take this into account when training and competing in hot, humid climates. With prolonged exposure to these conditions, your body acclimatizes, or adapts to the heat, but this does not happen in one workout.

In the cold, the opposite response kicks in. As the outside temperature drops, oxidative processes intensify as a reflex response, and body temperature rises. At the same time, muscle tension increases, and muscle contractions and goosebumps may occur. These responses increase heat production.

Your body also reduces heat loss. The blood vessels in your skin constrict, less blood flows through the skin and your body loses less heat. At low temperatures, higher humidity increases heat loss. Repeated exposure to cold helps your body adapt to it, but even then, you should not underestimate cold, wet weather.

Heat exchange and warming up before training

Physical activity increases both heat production and heat loss. This is one reason for warming up at the start of training. A moderate rise in body temperature prepares your muscles, joints and nervous system for activity.

A rise in body temperature of 1 degree increases the excitability of the central nervous system, supports internal organ function and activates oxidative processes. The simple truth is that your body moves better when you do not start exerting yourself completely cold.

A good warm-up does not need to be long or complicated. Start with gentle movement, add joint mobility exercises and increase the training load gradually. If you are preparing for strength training, use lighter weights for your first sets. If you are about to run or play a ball sport, let your heart rate rise gradually.

Practical signs to watch for during training

In a hot environment, pay attention to how you feel right from the start of your workout. Headache, chills in hot weather, nausea, unusual weakness and confusion are signs you should not push through. If these occur, you need to reduce the training load, move somewhere cooler and let your body settle down.

In the cold, the risk is different. Everything may feel fresh and pleasant at first, but wet clothing cools you down quickly. When you stop moving, heat production drops. That is why wearing layers in cool weather and having a dry layer to change into after your workout are important.

Honestly, the best solution is often simple: choose a pace that suits the conditions, do not stubbornly push through to the end of a workout in an overheated room, and warm up properly. Heat exchange happens all the time, even when you are not thinking about it.

FAQ: heat exchange and training

Why is training harder in humid heat?

In humid air, sweat does not evaporate readily from your skin. You may sweat a lot, but the cooling effect remains weak. As a result, the risk of overheating rises more quickly.

Do you also need to worry about overheating in the cold?

At a very high training load, your body can produce a lot of heat even in the cold, but cooling down after you slow your pace is usually the greater concern. Wet clothing and wind accelerate heat loss.

Why does warming up help prevent injuries?

Warming up raises your body temperature moderately, prepares you for movement and helps you adapt to the training load more quickly. It does not automatically make your workout safe, but it makes the transition from a cold start less abrupt.

Author: Kristjan Koik

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