Dehydration in runners: causes and consequences

When you run, you sweat. When you sweat, you lose water. Like all athletes, you replenish your supply with water or recovery drinks. But can you drink enough water to stay hydrated on hot days with high humidity? It turns out not. At the same time, dehydration or dehydration threatens not only with an unpleasant feeling of thirst, but also with a significant decrease in performance. Why is this happening and how to get rid of it?

When you run in hot and humid weather, you lose fluid at a high rate, faster than you can replace it. The longer you exercise, the more water deficit your body becomes, and it doesn't matter how much water you drink during or after exercise.

To understand how dehydration affects your running performance, you must first understand what happens to your body when you run in heat and moisture.

Temperature and blood volume

During exercise, your body tries to maintain an optimal temperature and draws blood to your skin to keep you cool. Meanwhile, your muscles generate heat as you convert your body's natural fuel into energy for running.

The hypothaloamus detects a rise in temperature and activates the sweat glands. Water, which helps cool the body, that is, sweat, is released and evaporates, taking moisture from the body, so the end result of this process is a decrease in blood volume.

In a simple way, this state of the body can be called "thickened blood". At the same time, your muscles need a lot of oxygen to function. More oxygen means more blood flow to the muscles.

Putting all these facts together, it turns out that your blood is thickened because you sweat and less blood flows to your skin and muscles. The body has fewer and fewer opportunities to cool itself and deliver the right amount of oxygen to the working muscles.

What does heat and humidity have to do with it? On hot days, you sweat more, and on days with high humidity, your sweat-producing "cooling system" works less efficiently because the moisture in the air prevents sweat from evaporating from the surface of your skin.

When the volume of blood becomes less, the body tries to retain fluid and reduces the production of sweat and the rate at which blood is delivered to the muscles. This makes your muscles work harder, and you may even have a fever on a hot day. If you have a chill, stop exercising immediately.

Water Loss Rate: More Than You Can Replenish

On very hot and humid days, a runner can lose about 1.5-2 liters of water in one hour. Some of this amount can be replenished by drinking water during exercise, but in any case, your stomach can only absorb 180-210 ml of water every 15 minutes. At this rate, you can only replenish 720-840 ml per hour, which is much less than the lost 1.5-2 liters. And if you lose so much water every hour, dehydration sets in.

And the longer you exercise, the greater the water scarcity. Imagine that on a hot day you are losing 1.5 liters every hour. Even if you drink a liter every hour, your stomach will only be able to absorb about 800 ml (and the rest will dangle in your stomach while you run). So you will have a deficit of 200 ml of water every hour. In two hours, the deficit will already be 400 ml, and most likely more, because during training you will not drink one and a half liters every hour.

At this rate, in a four-hour marathon, you will lose 1.5 liters of water, and this is a significant figure.

Dehydration reduces results

Dehydration studies in competitive sports have shown that every percentage of dehydration weight loss makes you 2% slower.

For example, if an athlete weighs 56 kg and then loses approximately 1.3 kg per hour, in two hours she will lose 2.6 kg, which is about 5% of her weight. These 5% worsen her performance by 10%, and if before that she could run 2 km in 10 minutes, after two hours of running her performance will deteriorate by 1, 2 minutes.

Of course, you can replenish the water supply, but the losses will still be too great and the indicators will deteriorate by a certain percentage.

Preparation and recovery

You can't avoid water loss while running, but you can reduce your water deficit by getting enough water before your workout and by recovering during and after.

Drink at least 1.5-2.5 liters of water throughout the day before training, especially during the warmer months.
Drink 0.5 liters of water at least one hour before your workout.
During your workout, try to drink 200 ml (1 cup) every fifteen minutes, even if you don't feel thirsty.

After training, it may take a day or two to fully replenish your water supply. Remember that your body can only absorb about 800 ml of water per hour, and if you lost 1.5-2 liters or more, it will take several hours to simply absorb that amount of water, let alone the fact that few people drink two liters of water in one evening.

In addition, not all of the water is absorbed, because some is excreted in the urine. Therefore, you should continue to drink regularly after running to make up for the loss before your next workout.