Hydration during training and racing

We are fast approaching Ironman NZ and NZ is having a week of unprecedented high temperatures. And so hydration during and after training and racing is an important factor to consider.

There are probably three different things you can consume during training, plain water, rehydration solution and sports drinks. These are all different and the first two at least have different places in your hydration strategy. Opps I forgot a fourth – coke – liquid gold. In order to understand their role in your hydration plan, whether it be training or racing, you need to understand the physiology of hydration.

When you drink, the fluid moves down into your stomach and if you have only consumed fluid it moves quickly into your intestines to be absorbed. Your intestines are set up with a rich supply of blood and a single layer of cells separating the inside of your intestines from your blood suppply. Water just has to pass through this layer of cells and you have got it to your blood to do all the good things it does, primarily maintin your blood volume so that it doesn’t get too thick and can keep taking oxygen and glucose to your muscles. The body is pretty clever and sets up things called gradients to help move things between different compartments (here it’s between the intestines and the blood). Gradients are simply one compartment with a high concentration of something and the other has a low concentration of something. If you are in a really full train or lift and the doors open, your instinct is to spill out into that area where there are less people and the body is the same. If something is in the area of high concentration, it wants to move to the area of low concentration in order to get more room. The concentrations we want to look at here is water (osmotic gradient), glucose (sugar) and sodium (salt).

The layer of cells separating the intestines and the cells are set up to move sugar and salt rapidly from the intestines into the blood so that you can use these for energy and other cell  processes. By moving sugar and salt across we change the osmotic gradient which results in sucking water into the blood as well. Rehydration solutions such as hydralyte that you give kids when they are sick are formulated on this principle. If you add a little sugar and salt the act of absorbing these into the blood stream also pulls water into the blood and promotes the rehydration process. Straight water doesn’t have this drive, a little bit of water will be absorbed but it’s much more efficient to aid the transport of water with sugar and salt. A number of sports nutrition companies such as nuun, osmo, Pure and SOS to names a few have used this strategy in formulating their rehydration fluids. Note that I don’t call them sports drinks because sports drinks typically have much more sugar in them and so change the whole process.

Take home message from that: Having sugar and salt in your intestines with the water makes you absorb the water faster.

That sugar and salt doesn’t need to be mixed in with the water in the form of a drink though to do it’s work. If you have eaten something or had a gel, then you already have sugar and salt sitting in your stomach and so add plain water to that and you have created a condition which facilitates hydration.

And here is the important thing to understand. If you add too much sugar or salt (in endurance athletes the sugar is generally the issue) say in the form of having a gel and washing it down with a Nuun, then you have suddenly created a situation where the high concentration of sugar and salt is not in the blood pulling water into the blood, it is now in the gut. Your intestine cells will be transporting the sugar and salt into the blood like mad but it won’t be fast enough to fix this gradient issue. And when the sugar is high in the gut, then water wants to move towards that area in order to fix the osmotic gradient. I sometimes tell my students this is like a high and low water concentration. High sugar means low water and so the water actually moves out of the blood and into the stomach. And yes this IS a problem for two reasons. Firstly, we are trying to maintin blood volume to aid performance and so pulling water out of the blood into the intestines means our blood volume just went down, the blood gets thicker. Its harder for the heart to pump it to the working muscles. Oxygen and glucose delivery to the muscles slows and suddenly it feels a whole lot harder to maintain your level of exertion. Secondly, you have just increased the volume of stuff in your intestines. This is often accompanied by a sloshy feeling in the gut and very often GI problems, worst case scenario – diarrhea because the contents in your gut has heaps more fluid in it. Fluid that should really be maintaining your blood volume. And your gut doesn’t adapt so well to these rapid changes when you are exercising and so this issue of too much sugar in the gut is often the cause of GI problems that in particular runners experience. We don’t want to be stopping every 5 minutes for the loo and equally we don’t want to make it any more work for our heart to circulate the important stuff to the muscles so they can work.

Take home: Whether it is training or racing, rehdration fluid has it’s place (but not sports drinks – the carb content is too high) and that place is as rehydration when you have nothing else in your stomach. When you have just eaten or had a gel then wash it down with water and when it’s a gel you really need to drink about half a bottle of water (but thats something to discuss in a different post).

Now for coke – or as I call it, my happy juice. It’s a high concentration of sugar, salt and that all important caffeine. This needs to be washed down with some water. I actually dilute it one cup coke, one cup water put them together and drink it down on the run. [Don’t try this when not racing – it tastes feral at any other time].

I recommend all my athletes to use both water and Nuun ( or Pure the electrolyte on course at IMNZ) one bottle of water to every bottle of Nuun to keep it simple and to make sure they aren’t getting too much carbs in their gut at any one time. When it comes to the run, if you have had a gel or a blok/chomp etc then its water at that aid station. Aid stations in between i personally go for coke and water but rehydration fluid is also a great option. But don’t mix gels and coke, or gels and nuun.

Stay tuned for post-workout rehydration.


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