In nutrition Part 1 – What’s All This Fat-Burning About? and Part 2 – Fuelling Your Races (which are available from the blog) we discussed the benefits of fat burning and how to fuel correctly on the day of the event. In part 3, our focus is hydration or in more simple terms how much to drink.
Your body needs fluids for various functions. Body cells and tissues are filled with fluid, the nervous system requires fluid and the fluid component of your blood (known as plasma) is also affected by your drinking habits. Exercise leads to a loss of body fluids via sweating and breathing and this loss of fluid can eventually lead to what is commonly termed dehydration.
What happens when we drink?
When you put fluids into your stomach, they pass through the stomach wall into your blood vessels and effectively become plasma. As your blood stream can pretty much reach any part of your body, any tissue or any cell, this fluid can be transferred from the blood stream into the tissues or cells.
How does fluid actually pass from one place to another?
To get the fluid from your stomach into your blood stream or from your blood stream into tissue cells requires a process termed ‘osmosis’. Salt acts like a magnet drawing fluid towards it and the concentration of salt in your blood and tissues determines the shift of fluid around your body.
When you take a drink of water it reaches your stomach and waits excitedly to pass through the wall into your blood stream. Your blood is saltier than the water in your stomach and due to the higher level of salt in the blood, the water is drawn from the stomach, through the wall and into the blood. This water effectively becomes blood plasma and travels around your body. If it finds muscle tissue which has a higher salt concentration, the magnetic pull of the salt within the muscle will draw the fluid from the blood into the muscle.
In simple terms, when something is dehydrated, it becomes more salty. By becoming more salty it’s magnetic pull increases in power and it attracts water towards it. That’s how fluid shift and hydration works within the body, that’s ‘osmosis’.
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What happens when you dehydrate?
When you dehydrate your tissues and blood have less fluid thereby making them more salty, in the hope that they can attract fluid towards them. Your blood becomes thicker as you still have the same amount of ‘blood cells’ but the fluid component is reduced, thereby making it more concentrated. Not only does the blood become thicker (making flow more difficult), the absolute amount of blood is also reduced so you have to pump the smaller blood volume more quickly around the body, thereby increasing heart rate.
So how much should I drink?
Most text books will recommend somewhere between 1 – 1.5 litres per hour depending upon individual sweat
rates, but it is unlikely that this amount can actually be absorbed when you are exercising. As each litre of fluid weight 1kg in weight, it is possible to calculate (very roughly!) fluid loss by taking weight before and after.
The Endurance Coach research on ultra distance runners
Last year we measured pre and post body weights for competitors taking part in a 100 mile mountain running event www.lakeland100.com. Race finish times varied from 24 to 40 hours and if we presume that athletes are losing 1-1.5 litres per hour, just how much weight did the competitors lose???!!
The body weight stats 2010
Our stats from last year showed the followed weight loss at the finish line:
1. Runners sub 30 hours, average weight loss 860g / 860ml
2. Runners sub 32 hours, average weight loss 1008g / 1008ml
3. Runners sub 35 hours, average weight loss 1040g / 1040ml
Compare those figures to the guidance given in the previous paragraph which suggest that athletes will need to replace 1-1.5 litres per hour as this is the rate at which they are losing fluid. Admittedly the competitors may not be exercising at a very high intensity due to the nature of the event, but even then… something doesn’t add up as the fastest runners haven’t even averaged 1 litre fluid loss at the finish.
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I know I’m cynical. However, there needs to be some common sense applied to hydration. Your body tells you when you need fluid by making you feel thirsty and then you should drink what you’ve lost. Your body is very much like a water tank with an overflow system, once the tank is full, any further fluid intake will be dispensed with by urinating. It’s correct to say that urinating frequently and especially if the urine is clear, IS NOT a sign of optimal hydration, it’s a sign you’re drinking too much.
The drink might kill you…
For many years marathon runners were encouraged to drink at every aid station and “don’t wait until you’re thirsty.. it’s too late then!” Unfortunately a few of those people died as a consequence due to a condition known as ‘hyponatremia / hyponatraemia’ which is excessive dilution of body salts.
What’s going on??
Hyponatremia is quite simple:
1. Take 1 medium sized bucket, add a tea spoon of salt and then add 1 pint of water and in your bucket you have a salt solution.
2. Add another pint of pure water to the same bucket and you have now diluted the salt solution (it’s a bit weaker).
3. Add another pint of pure water to the same bucket and dilute the salt even further.
4. Keep going until the salt solution is so weak you can hardly even taste the salt.
We said earlier in this article that salt acts like a magnet and attracts water towards it:
‘When you take a drink of water it reaches your stomach and waits excitedly to pass through the wall into your blood stream. Your blood is saltier than the water in your stomach and due to the higher level of salt in the blood, the water is drawn from the stomach, through the wall and into the blood’
What if you’d added so much water to your body that the blood wasn’t salty at all, it was massively diluted and had thereby lost all its pulling power?
The chances of anyone dying from hyponatremia are so minimal and so infrequent that this should never concern you but weight measurements before and after can be an important part of medical checks. In essence, if you collapse and you’ve lost weight, we’d give you a drink, some food and a lift back home. If a competitor were to collapse and following a weight check they had gained weight, we would take it more seriously.
Some of you may be thinking at this point that you can take salt tablets with your water, if you add salt and water simultaneously, problem solved! The research has shown that it’s not a lack of salt intake which leads to hyponatremia, it’s too much fluid.
Drink sensibly, let thirst guide you and don’t force load yourself with water.
Aside from excess fluid intake, there is one other thing which may lead to weight gain during ultra distance endurance events and that is ‘rhabdomyolysis’ or ‘muscle damage’ leading to inflammation. This is a real issue for longer events and has a huge impact upon performance and health, so that’s the April newsletter article sorted then!
Take care out there…
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