Three bottles? Why would anyone, especially an elite tennis player challenging the World Number 1 on Centre Court, have three different sports bottles?
Watching Naomi Osaka’s straight sets victory over Sabalenka, I started to wonder what she or her team had decanted into three Evian-branded bottles – and how it might have helped this slightly built athlete outplay the powerful, statuesque Belarusian in 28-degree heat.
At a guess, those three bottles contained three different types of hydration fluids: pure water, to help clean and refresh the mouth; a carbohydrate gel for energy; and an electrolyte and water infusion.
Every sportsperson is conscious about hydration and the content of that fluid. Electrolytes are key here, as on the simplest level, electrolytes allow you to physically take in more water. This is something I’ve always found amazing – that water alone is less effective than water with electrolytes for hydration. It’s important to double down here, as if you are exercising and sweating, you’re losing electrolytes. If you replace that lost sweat only with water, you are potentially putting yourself at harm because you’re not replacing your electrolyte losses and you are diluting what you got remaining as well.
That can have negative health consequences.
Water intoxication is an all too common cause of the death of marathon runners. People who drink enough from a volume perspective – being the key 400–800 ml of fluid per hour, if they limit that to just water, can lead to this water intoxication, technically termed hyponatremia, or a blood sodium <135 mmol/L, due to the double effect of loss and dilution.
To put this in perspective, one review of Marathon finishers has >10% of runners technically with a sodium level in keeping with hyponatraemia!
So what is the issue here? “Water follows down-hill”, or more accurately, will move down a gradient, so if someone has developed hyponatremia, there is more sodium inside the cell, meaning water will flow down the gradient from the low sodium around the cell, to the higher sodium within the cell. Science lesson short, hyponatremia causes your cells to swell, which is about as dangerous as it sounds, especially if those cells are brain cells, leading to headache, drowsiness, irritability, thirst (which exacerbates the effect), cramps, and muscle twitches.
That muscle twitch doesn’t sound too risky, until you remember the heart is a muscle. Yes, hyponatremia can cause palpitations and arrhythmia, due to cellular electrical instability.
Takeaway: electrolytes and sports aren’t just about performance; they’re about safety.
When we talk about electrolytes, we’re not just talking about sodium chloride; the next highest electrolyte in most sports drinks is potassium. This is why electrolyte supplements will say “use one a day” as excess potassium is not a good thing. So, for example, if somebody is taking excess electrolytes, which is always a possible risk when you’ve got hot weather, and you find one that tastes nice. You think, right, I’m sweating. I’ll have another one of these.
Now, hopefully, your kidneys would be able to say, gosh, there’s too much potassium here and dump it into your urine. But if anything is going wrong with your kidneys, you’re not able to deal with that excess potassium, you end up with hyperkalemia, which can cause life-threatening arrhythmias, such as ventricular fibrillation, where your heart goes from a nice controlled pumping contraction to shaking. Obviously, that’s bad news. Hyperkalaemia is the gift that keeps on giving; there is the risk of a different arrhythmia, asystole, where the heart doesn’t fibrillate, it just stops.
While sounding frightening, potassium is vital for your health, and it is important to have it in electrolytes to replace losses. You’ll see on electrolyte packets to “not exceed recommended intake”, which approximates to a daily total intake of 3,400 mg (men) and 2,600 mg (women).
So how much should we be using? The obvious answer is to repeat the “do not exceed recommended intake” advice. But, given that we are talking about extra losses due to sports, and everybody’s sweat is different, there are some rules of thumb we can use here.
Keeping in mind that whilst you may drink fluid, it hasn’t actually entered your body yet, it has to be absorbed, and you can only move so much fluid out of the bowel. In terms of total intake, during intense exercise, it is reasonable to aim to consume 400–800ml of fluid per hour, but keep in mind you may need to continue replacing, as the sweat level is personal, with a range from 400-2400ml per hour depending on the person, and their heat adaptation.
Again, the level of sodium loss in people’s sweat will vary from person to person – but 700 to 900 milligrams of sodium per thousand ml of fluid taken is likely to be sufficient and safe.
What about the carb gel? There have been some interesting studies from the world of cycling where they had people take the gel and swallow it, and then they had people take the gel, swish it round their mouth, and spit out. And both groups performed better than the person who didn’t get the gel at all.
As for the straight water: that’s good for your dental health, no question. We know that sportspeople get a lot of dental caries – possibly due to the presence of stress. Think Centre Court, and a much larger and stronger opponent who is ranked Number One in the World. Then there’s the grunting. Osaka almost certainly had a dry mouth.
Optimising hydration is key to performance. I always think of Chris Froome’s colossal effort to breakaway during the Tour de France mountain stage, when he found a superhero thrust to pull away from the pack. Froome had multiple bottles – and he had to drink each bottle at set times and in set orders to replace what his team knew he was losing: the exact balance of carbohydrates, fats, proteins, and electrons. It was a team effort to get the bottles to him in the correct order and make sure they were correctly temperature-controlled. It was a perfect example of the science of sport enabling success.
As a Doctor Finlay’s patient, you too can have your own back up team including professional analysis of your sweat to determine what you need to have in your water bottles to improve your performance.
Whatever your hydration strategy is, I’d strongly advise that you don’t copy Sabalenka when she lost – and get drunk.
