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Today I'm going to take a look at the aspects of hydration I am most asked about. I'm asked about them because there is a lot of mixed information out there. Where possible I've included links to the science for you to look more deeply into it.
Cramps are a hard topic to study as they are very individual and hard to simulate in the lab but science does have a dominant theory. It is believed cramps are caused by neuromuscular fatigue, not by a lack of electrolytes. Of course the scientists at Gatorade would love us to believe differently. When one of my swimmers has a cramp the first question I ask is whether they ran that morning or perhaps had a hard workout the day before. The answer is invariably 'yes'. Muscles are designed to contract and relax. When the nerves controlling that action are fatigued they can sometimes have trouble with the relax part. That leaves the muscle stuck in contraction.
Some people are just more susceptible to cramps and in specific muscles. Avoiding placing demands on already fatigued muscles is step one in helping to avoid the lock up. Secondly, doing a gentle stretch or activation of the troublesome muscles in advance of exercise can help too.
Let's talk a little about the main electrolyte now, sodium. We do lose sodium in our sweat but it's important to know that we lose a lot more fluid than we do sodium. As we lose fluid the sodium concentration can actually increase. Our body does a good job of monitoring the sodium content in our blood and accesses stores to ensure a safe level is maintained under most circumstances. It also releases less in our sweat when it's needed internally or releases more if there's an excess. The problem comes when athletes drink more than they need, more water or sports drink. This results in a dilution of salt content in the blood, and a serious condition called hyponatremia can follow. Sports drink does contain some sodium but studies have shown that it's not enough to measurably counteract over-hydrating. Consuming more fluid than your body needs is dangerous.
When it comes to hydration independent science (independent of commercial interest) shows that drinking to thirst is the best approach. Our brain monitors our systems carefully and the thirst mechanism is there to address any imbalance. While there is no consensus most studies support that a 2% drop in fluid weight over the course of an event does not result in a drop in performance or function so you don't have to worry about replacing every bit of fluid you lose. The bottom line is: drink when you're thirsty and avoid over-drinking.
A question I get every year is 'should I take salt tablets during my Ironman?' Science has shown that they do not measurably increase the salt concentration in the blood of endurance athletes so salt tablets won't protect you from hyponatremia. Anecdotally though, some athletes will tell you that they felt better after taking them. What could be at play here? I see three possibilities: 1) they act to reset the palate after so many sweet carbs (gels etc), 2) in some cases sodium can help the gut better absorb carbs and, 3) placebo effect. So, should you take them? It's your call. Just know why you're doing it and don't over-drink.
We've established that you shouldn't over-drink. So how do you know how much to drink? Here are some recommendations.
Monitor the colour of your urine daily to gauge your level of hydration. It's a practical step to get a general idea.
Make sure you're not dehydrated to start a workout or event. Sip to thirst beforehand.
During activity drink when you're thirsty
Through experience learn what your own personal needs are under different conditions. The conditions we're paying attention to are: duration, intensity, air temperature, and humidity. Get a general idea of what your needs might be and plan your fluid supply accordingly.
Plans must be flexible. You must never blindly follow a plan. Your intake must be adjusted for the variables above and how you're feeling. Listen to your thirst.
If you want to take it a step further you can weigh yourself unclothed before and after a workout to check for a change in water weight. If you lose over 2% of your body weight you may want to consider slightly increasing your intake in the future depending on how far over 2% you are. If you lose NO body weight it may be an indicator that you consumed a little too much. Losing up to 2% is a normal experience and not unhealthy.
In replacing fluid after activity there is a simple ratio you can use and that is 500g equals 500ml. Some science recommends replacing fluid loss with a range of 100% to 150% of that lost.
*A final word of caution. Be careful relying on fluids as your source of carbohydrates during long activity sessions (ie over 2hr). You may need the carbs but not the fluid and this can lead to over-hydration. Count the carbs in your drink in your total intake but focus on food more for your carbs.
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