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Melanie McGrice is an Accredited Practising Dietitian and author
Did you know that an average athlete is about 60% water?
Our body is very complex and carries out hundreds of chemical reactions each day, and most of these require water. This is why hydration - the process of providing an adeqaute amount of water to the body's tissues - is so important to get right.
Dehydration most commonly occurs in exercise when the fluid lost due to sweating is not properly replaced. The repercussions can be detrimental in terms of athletic performance. In a study performed by Shiffeffs and Sawka (2011) it was found that dehydration degrades aerobic performance in athletes. This occurs because dehydration influences cognitive function, mood and mental readiness. Dehydration has also been shown to increase the level of perceived exertion, which means that when you are dehydrated and exercise, you will feel you have worked harder than you actually have and this causes a reduction in your performance. So how can you avoid dehydrating yourself? The most obvious way would be to drink more water, right? Almost. You do need water, but you also need to ensure you are getting enough electrolytes.
We’ve all heard about them, but what exactly are electrolytes? Electrolytes are the body’s salts and minerals that are important for maintaining the fluid balance in the body. Probably the most important one for us is sodium, as this is the mineral that lives in the fluid outside of your cells, the extracellular fluid.
When we sweat, we lose some of our body’s water, but we also lose our electrolytes. This happens because electrolytes and water are friends and like to travel together. Surprisingly, it’s not excessive sweating that has the greatest impact on electrolyte concentration, it’s actually the way we rehydrate ourselves. After sweating profusely, rehydration with straight water dilutes our extracellular fluid and thus reduces the electrolyte concentration.
So what can you do to replace all these lost electrolytes? Drink them back in! Before endurance exercise it is important to consume some sodium-containing liquid to help retain the fluid consumed. When electrolytes and water are consumed together, they like to stay together, causing your body to retain the water you’ve just consumed. During exercise straight water is ok, unless the duration of your exercise reaches over 2 hours or the sodium losses through sweat are great, then you may need some additional electrolytes. Finally, after endurance exercise it is important to replenish the lost electrolytes by consuming them with water.
There are a few key things to note when it comes to replacing lost electrolytes. Firstly, you need to be choosing an electrolyte-replenishing fluid that is right for your exercise regime (if you don’t know, it’s always good to see a dietitian). This may involve something with both an electrolyte AND a carbohydrate, or electrolytes alone. A drink containing 50-90mmol/L of sodium provides optimum rehydration, but many sports drinks only contain around about 10-15mmol/L.
Here is a list of some common drinks and when to drink them:
Too much plain water too quickly can dilute your electrolyte concentration and cause you to run to the bathroom. You want to achieve rehydration, not that sloshy feeling you have when you drink too much too quickly. Aim to rehydrate slowly, by taking regular sips before, during and after exercise so that it replenishes and maximizes absorption for not only your fluids, but your electrolytes too. It depends on the type of fluid (as fluid with electrolytes is absorbed better), but most authorities say that you shouldn’t drink more than about 600ml of water every hour if you want to avoid a ‘sloshy’ tummy.
This information is all well and good, but putting it into practice is a different issue. Fluid balance can be very individual, especially when you throw exercise into the mix. How can you find out what your fluid requirements are? How can you find out the best way to rehydrate? At Nutrition Plus we have a highly sensitive bioelectrical impedance machine to measure individual’s body composition. This machine uses a small, harmless electrical current to measure the body tissue’s resistance to the electrical flow. From this, it determines your muscle, fat and fluid mass.
The review by Shirreffs and Sawka also found that many athletes begin a training session in a state of fluid deficit, meaning that before you’ve already started you’re doing yourself a disservice! Getting regular fluid balance check-ups can be a key strategy in improving your exercise performance.