Sweating and fluid balance during training
Sweating is your body’s natural defense mechanism — without it, your body would dangerously overheat during training. But do you know exactly why it happens and what you should do to maintain your performance?
Why do you sweat?
Your body is a pretty clever machine. When your muscles work intensely, your body temperature rises and your body responds by producing sweat. As sweat evaporates from your skin, it cools your body — a thermoregulatory response that prevents overheating.
Every gram of sweat that evaporates from your body carries away 0.58 kcal of heat energy. There is an important detail here, though: only sweat that actually evaporates cools you down. Humid air or clothing that is not breathable reduces evaporation, making thermoregulation less effective. That is why training in a stuffy gym in summer is much harder than in a well-ventilated space.
Sweating and dehydration: what does your body lose?
So what actually happens when your body loses too much fluid?
Dehydration reduces blood plasma volume. Since the cellular components of your blood — red and white blood cells — remain unchanged or even increase in concentration during physical exertion, your blood becomes thicker. Thicker blood makes your heart work harder: to supply your working muscles with enough oxygen, your heart has to beat faster than usual.
Observations from US laboratories, on the other hand, show that a moderate increase in the body’s water content can actually improve performance. The simple truth is that you need neither too little nor too much — fluid balance is critical.
Water in your body is divided into two compartments: intracellular water (about 50% of body weight) and extracellular water (about 20% of body weight). During training, you mainly lose extracellular fluid, which needs to be replaced quickly.
What should you drink to maintain performance?
Many people think plain water is enough to replace what you lose through sweat. In reality, that is not quite the case.
Along with fluid, you lose electrolytes through sweat — sodium, potassium and magnesium. If you drink only water with a low mineral content, it dilutes your blood: the concentration of electrolytes and other osmotically active substances in your plasma falls. Water then starts moving into your cells to restore osmotic balance. This condition is called hypotonic hyperhydration — and it can cause cramps in your working muscles.
For longer or more intense workouts, it therefore makes more sense to drink mineral water or drinks containing electrolytes than plain tap water. A short, light workout lasting up to 45 minutes is an exception — ordinary water is enough.
The truth is, thirst is not always a reliable signal. By the time you feel thirsty, dehydration may already be affecting your performance. Drink a little before your workout, a little during it, and make sure you drink afterward.
FAQ: frequently asked questions about sweating
Does sweating more mean your workout is more intense?
Not necessarily. How much you sweat also depends on the surrounding temperature, humidity, the fabric of your clothing and your individual thermoregulation. Trained athletes often start sweating sooner because their bodies have optimized their cooling systems — this is actually a sign of good fitness, not weakness.
Is weight lost through sweating real fat loss?
No. Weight lost through sweating is almost entirely fluid loss. That weight returns as soon as you drink again. Weight loss through dehydration is harmful to your health and completely ineffective in the long term.
When should you pay particular attention to your fluid intake?
In summer, in hot and humid conditions, or during workouts lasting more than 60 minutes. You should also pay attention if you notice that your urine is very dark — this is a clear sign of dehydration that you need to act on immediately.
Come work up a sweat! ArtGym
Author: Compiled by Ero Viik
Source: WHO – Physical activity.
