Fluid balance: Fluid out vs. Fluid in
When talking about hydration, it’s useful to think in terms of fluid balance, meaning the difference between the fluid that is going out of your body vs. the fluid that you are taking in.
Even the fittest of bodies is surprisingly inefficient in terms of its energy use, and a huge amount of energy is wasted as heat, especially during intense exercise. It’s critical that we dissipate (or get rid of) this heat, in order to maintain normal body temperature, or else body temperature would rise extremely quickly, affecting vital biological processes.
When we sweat, the sweat evaporates, and carries the heat energy away from the body, into the air (imagine the steam evaporating from a pot of rice, where the heat energy is being taken away from the rice into the air), helping to maintain the body temperature at a safe level. i.e. sweating cools us down.
As athletes, we can sweat out litres of water during training sessions and matches, and the amount will depend on various factors, including your physical attributes, activity intensity, length of the activity, and environmental heat and humidity.
Urination is one of the body’s mechanisms for getting rid of waste products, controlling blood volume and controlling amount of electrolytes in the body. These are all tightly regulated, and don’t need a huge amount of conscious effort on your part, apart from the few recommendations I’ll give later around altering fluid consumption.
The amount of fluid that you lose through urination is largely dependant on the amount you drink. As well as being affected by other aspects like electrolyte levels and how much you are sweating.
Fluids are also lost through breathing (the air we breathe out is high in water vapour), and excretion. These aren’t as relevant to this article, so I won’t go into depth on them.
The fluid we take in can be in the form of water and other beverages, as well as some foods, like fruits and vegetables, which tend to have quite high water content.
Consuming sufficient fluids is crucial for athletes, in order to match the fluids being lost through sweat and urination, or we risk seeing the negative effects outlined below.
Negative Effects of Under-Hydration
1. Heart Rate
There was a study done that assessed two groups of athletes in the same running session. One group consumed water during the session and the other didn’t.
The results showed that heart rate was significantly higher throughout the session in those who didn’t consume water, insinuating that the same exercise session was more strenuous when under-hydrated.
The proposed reason for this is that as you lose fluid, your volume of blood decreases, meaning the blood is more concentrated and thicker, and therefore the heart has to work harder to pump it around the body, as it aims to circulate nutrients and remove waste products.
2. Temperature Regulation
As mentioned earlier, sweat helps regulate body temperature by dissipating heat from the body i.e. it cools us down.
When we’re dehydrated, we sweat less, and therefore the body will either increase in temperature to the point of causing harm, or you will be forced to reduce intensity due to the discomfort of overheating. Either case will result in performance being diminished!
3. Electrolyte Levels
Electrolytes are electrically charged particles, which are involved in carrying electrical impulses around the body, and are involved in the nervous system and contracting muscles, both of which are extremely important for athletes. They are also involved maintaining hydration levels in and out of the body’s cells.
The main electrolytes include sodium, potassium, chloride, bicarbonate, calcium, phosphate, magnesium and others, all with their own functions.
We lose some of these through sweat, and if we don’t replace them and they get too low, we can see issues with muscle cramping, fatigue, and ultimately a downturn in athletic performance, or worse than that, health risks.
The Rare Case of Over-Hydration
There have been cases, mainly during long-duration events, where people have had serious health issues, and even died after drinking too much water during the event.
Although they were following wise advice in replacing the water they were losing through sweat, they weren’t also replacing the electrolytes lost through sweat, resulting in the sodium content of the blood becoming diluted, which leads to complications with cell swelling.
This isn’t a likely concern for GAA players, as athletes in general typically find it difficult to consume a lot of water during training and matches, but I use this example to show that there is a limit to how much you should be drinking, so taking multiple litres of water in directly before a match or at half-time, for example, isn’t going to be a good idea, and sipping on water throughout is a better idea.
I also use it to point out that when you are drinking a lot of water, for example during an intense championship match in the summer heat, it’s probably a good idea to add some electrolytes to your water, either in the form of a pinch of salt, or an electrolyte supplement, in order to replace the electrolytes lost through sweat.
All of this might have you feeling overwhelmed as to what you need to do with this information.
The good news is, the body is extremely good at regulating all of this. If you drink too much, your body will excrete more. If you consume too much salt, your body can usually adjust, and so on.
The main thing we have to do is to avoid the extremes.
With that said, performance usually goes down at about 2% water loss, and thirst usually starts between 1-2%, meaning that if you turn up to a training session or match feeling thirsty, you are already selling yourself short, as it is usually difficult to drink enough during the session or match, to match the amount you are losing through sweat and exhalation, resulting in further dehydration and further performance detriment.
General Daily intake
The amount you should drink will depend on a lot of factors, but generally about 1L per 25kg bodyweight (3L for a 75kg athelte) will be a good starting point, along with seasoning your food and eating plenty of fruits and vegetables, in order to ensure adequate electrolyte intake. Urine colour should also be monitored, ensuring regular, clear urinations throughout the day.
During matches and training sessions, a good starting point is to simply consume fluids at natural breaks in the game, aiming for 1-2 mouthfuls every 10-15 minutes, with slightly more during half-time.
This drink should generally be made up of water, with some electrolytes, and perhaps some carbohydrates (no more than 7% concentration) which can help with the gut’s absorption of the fluid, as well as allowing you to gain the performance benefits associated with carbohydrate supplementation. This tends to be exactly the composition of most sports drink, and now you know why!
After tough training sessions and matches, it’s important to start the rehydration process soon, which should involve sipping on either water or the pre-mentioned drink in the hours following the session.
Conor O'Neill, Know Yourself Nutrition
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