Effects of physical exercise on body temperature
Air temperature is the primary factor influencing the body’s function and its capacity for exercise. In hot weather, we tend to get tired faster, withdraw from certain activities more frequently, and in extreme cases, some individuals may experience heatstroke. Hyperthermia (overheating) poses the greatest risk when exercising on hot days.
The human body needs a significant amount of energy to generate power during training. Cycling, regarded as one of the most energy-efficient activities, typically achieves only about 30% efficiency. This means that to display a power measurement of 300 watts, the actual energy generated by the cyclist would need to be 1,000 watts. What about running? In terms of efficiency, running is even worse, at only 5%.
The remaining energy is mainly converted into heat due to metabolic processes occurring during physical activity. That’s why you feel hot when you exercise more intensely. Of course, there’s nothing wrong with the fact that exercise raises body temperature – problems arise only when the body struggles to adequately cool itself down.
When your body gets hot, it releases excess heat to the environment, cooling the blood that circulates near the surface of the skin. Your blood vessels dilate, increasing blood flow. Your sweat glands also become active – the sweat you produce evaporates, cooling the skin and helping to dissipate heat generated by muscle work and biochemical processes.
The skin acts as a ‘great cooler’ – but sometimes it’s unable to effectively manage excess heat. High temperatures outside reduce the efficiency of the human cooling system. When you produce more heat energy than you can release to the environment, other tissues in your body heat up. When excessive heat is generated, your body overheats, resulting in the following symptoms:
- feeling of tiredness,
- dizziness,
- nausea and vomiting,
- disturbed consciousness,
- ‘spots before the eyes’,
- pounding heartbeat,
- breathing problems,
- loss of consciousness.
In extreme cases of hyperthermia, life-threatening heatstroke can occur. The risk increases during intense sunlight, when overexposure to the sun’s rays can disrupt the thermoregulation center in the brain and meninges, leading to heat-related disturbances. The risk of hyperthermia or sunstroke increases when the body is dehydrated.
What does dehydration involve?
The human body is composed of about 60% water, and the percentage changes with age. Your body uses water on an ongoing basis for its normal functions: through breathing, sweating, and producing urine. You compensate for water losses by consuming food and beverages regularly. It’s generally recommended that a person should replenish 1.5–3 liters of water per day (in the resting state). However, intense physical exertion dramatically increases the demand for water. Why is that? Firstly, because of how the human body’s cooling system operates. If the body is not sufficiently hydrated, the volume of blood decreases. As a result, it releases heat less efficiently, and more energy is needed to transport it to blood vessels closer to the skin’s surface.
Under normal conditions, you typically sweat out about 500 ml per day. However, during physical activity, you can secrete as much as 1.5–2.5 liters of sweat per hour! Along with the water used up in the cooling process, you lose valuable micronutrients, including sodium, potassium, and magnesium, which play a crucial role in healthy metabolism and water balance. Without replenishing the body with electrolytes, you fall into a vicious cycle of dehydration. Insufficient water causes the body temperature to rise. This intensifies the need for water, but if the supply remains inadequate, the temperature continues to rise, worsening the dehydration, and the cycle continues.
Dehydration of the body is accompanied by the following symptoms:
- increased thirst,
- feeling of tiredness,
- apathy,
- headaches,
- muscle cramps,
- dry mucous membranes and tongue,
- excessive sweating (or no sweating),
- increased heart rate.
Even mild dehydration reduces the body’s physical performance and accelerates fatigue, as the circulatory system struggles to transport thicker blood due to insufficient water. Severe dehydration (9% or more of body weight) poses a serious threat to health and life!
Tips for hot weather: how to exercise safely
The Internet is filled with stories about professional athletes demonstrating just how far it’s possible to push the limits of human physical endurance. The truth is that even these athletes sometimes required medical attention due to extreme exhaustion. However, amateur athletes lack access to coaching staff or medical facilities, and their bodies are not well adapted to exercising in extreme temperatures. Therefore, our most important advice is: “Prevention is better than cure”. All the tips listed below stem from this rule:
Get accustomed to the heat gradually – everyone, to some extent, can adjust their body to exertion in hot conditions, but it’s safer to do it slowly, starting with shorter training sessions of lower intensity.
Wearing a T-shirt keeps you cooler – exposed skin heats up more in the sun, sweats more, and is also prone to sunburn and insect bites. Runners and cyclists do not exercise without a T-shirt – take a cue from them.
Ditch the cotton – sportswear made of sweat-wicking materials will help you maintain thermal comfort. The right outfit improves your comfort and protects your skin from unpleasant flare-ups.
Remember to stay hydrated – never go through a training session without replenishing fluids. As a last resort, tap water will suffice, but mineral water or an isotonic drink (even a simple homemade version) is better. If you’re preparing for an extended workout, always bring something to drink with you.
You can drink less, but more often – smaller amounts of fluids consumed regularly hydrate the body more effectively. Drink according to your body’s thirst signals, but avoid extended periods of activity without water.
Protect yourself from the sun – when exercising outdoors, avoid ‘islands of heat’. Opt for shaded areas with cooler ground to minimize sun exposure. Remember to protect your head. Prolonged exposure to direct sunlight increases the risk of overheating or heatstroke. If your training – such as biking – involves continuous exposure of certain body parts to the sun, use sunscreen cosmetics like SPF filters and sun blockers to prevent sunburn.
Take care of your eyes– prolonged hot weather often brings airborne dust and particles. Sports goggles protect the eyes from pollution and harmful UV rays.
Watch out for insects – a mosquito bite is not a concern, but ticks brought from a run in the woods pose a risk of disease. An insect sting, especially when combined with allergies, can result in a hospital visit. Choose your outfit according to the area where you exercise and avoid locations where insects could be a serious issue.
Avoid alcohol consumption – while some consider beer to be isotonic, they overlook the fact that it primarily acts as a diuretic, promoting dehydration. The situation is similar with high-proof alcohols – in their case, the issue of water loss is exacerbated.
Sometimes it’s better to exercise indoors – yes, we know it’s a shame not to take advantage of the beautiful weather. However, for elderly individuals with circulatory issues or those who simply struggle with heat, it’s safer to exercise in a fitness club. Air-conditioned facilities and guidance from a trainer are highly beneficial to health.
Important: Even the best of us have worse days. If you feel unwell in the heat, stop exercising immediately. Let go, relax, and enjoy a cool (not icy!) drink. Don’t jeopardize your health and life by pushing through your training plan at all cost.
References:
- Kozłowski S., Granice przystosowania, 1986.
- Szyguła Z., Lubkowska A., Wysiłek fizyczny w różnych temperaturach otoczenia, Fizjologia wysiłku i treningu fizycznego, 2011.
- Kaciuba-Uściłko H., Termoregulacja, Fizjologiczne podstawy wysiłku fizycznego, 2001.
- Sawka M. N., Burke L. M., Eichner E. R. i inni, American College of Sports Medicine position stand. Exercise and fluid replacement, Medicine & Science in Sports & Exercise, 2007.
- McDermott B. P., Anderson S. A., Armstong L. E. i inni, National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active, Journal of Athletic Training,2017.
- El Helou N., Tafflet M., Berthelot G., Impact of Environmental Parameters on Marathon Running Performance, PLOS One, 2012.
- https://corebodytemp.com/blogs/news/the-science-behind-overheating, dostęp: 25.06.2024.