Isotonic? Hypotonic? The mystery of sports drinks revealed. Maybe.

I pride myself on not being part of the herd and buying what everyone else does just because someone once said that it was good. I like to make up my own mind and that inevitably means doing a bit of research and buying cheap. My PT son had given me a recipe for isotonic juice, but sometimes I just want convenience so buying a pre-made drink is the way to go. But which one?

I rarely buy big brand names. Store named goods are usually just as good and often supplied by the same makers, so paying over the odds for a name isn’t my style. Today in Morrison’s Superstore they had their own isotonic drinks on sale at 50p for a 75ml bottle (a total bargain when compared to the likes of Lucozade Sport), but they also had their own brand hypotonic drinks. What’s the difference? It said nothing on the bottle and at a quick glance the only major difference seemed to be calories and carbs – the isotonic having more of both and salt – the hypotonic having 5% more.

When I got home I asked my PT son what the difference was and although his answer was good, I needed more definition so that I could decide if I’d wasted my money or if I’d got a bargain.

This is what I discovered.

First of all we need to drink to stop us from becoming dehydrated, that’s primary school stuff.  Sweating is the way in which the body maintains its core temperature but results in the loss of body fluid and electrolytes (minerals such as chloride, calcium, magnesium, sodium and potassium). Unless we replace these lost fluids and electrolytes it will lead to dehydration and eventually circulatory collapse and heat stroke. Not the best scenario.

The next fact was a bit more scary. It takes very little dehydration to severely impair performance:

% body weight lost as sweat Physiological Effect
2% Impaired performance
4% Capacity for muscular work declines
5% Heat exhaustion
7% Hallucinations
10% Circulatory collapse and heat stroke 

So, basically, don’t mess with hydration!

Now, I could bore you silly with additional information about electrolytes and carbohydrates, but basically what you and I need to know is that as we exercise for longer periods we need to replace electrolytes and fluid lost in sweat and also rebuild some of the carbohydrates we are using up in the form of glucose which we have stored in our livers to power our run. Water is fine if we aren’t running far, but it won’t replace lost electrolytes or carbohydrates and it tends to bloat you up and suppress thirst.

So here’s the bit I was looking for, which drink is most suitable.

Isotonic – quickly replaces fluids lost by sweating and supplies a boost of carbohydrate. This drink is the choice for most athletes – middle and long distance running. Glucose is the body’s preferred source of energy therefore it may be appropriate to consume Isotonic drinks where the carbohydrate source is glucose in a concentration of 6% to 8%.

Hypotonic – quickly replaces fluids lost by sweating . Suitable for athletes who need fluid without the boost of carbohydrate.

Hypertonic – used to supplement daily carbohydrate intake normally after exercise to top up muscle glycogen stores. In ultra distance events high levels of energy are required and Hypertonic drinks can be taken during exercise to meet the energy requirements. If used during exercise Hypertonic drinks need to be used in conjunction with Isotonic drinks to replace fluids.

So basically my hypotonic drink is fine for short runs instead of water, if I wanted. I tend not to take a drink with me if I’m running less than 4 miles. Up to 6 and I tend to take just water, but I could take a hypotonic drink. If I’m running for up to two hours or more then I definitely need an isotonic drink. I would imagine that a hypertonic is roughly equivalent to taking a gel, which I’m not keen on using (sticky fingers, littering the route), but taking two drinks isn’t convenient, so I’m still happy taking my Dextro tablets at intervals alongside my isotonic drink.

Last thing, for those wanting to save some wonga, here are a few recipes:

Making your own!

Isotonic – 200ml of orange squash (concentrated orange), 1 litre of water and a pinch of salt (1g). Mix all the ingredients together and keep chilled

Hypotonic – 100ml of orange squash (concentrated orange), 1 litre of water and a pinch of salt (1g). Mix all the ingredients together and keep chilled.

Hypertonic – 400ml of orange squash (concentrated orange), 1 litre of water and a pinch of salt (1g). Mix all the ingredients together and keep chilled.

Now, to put this into context, I’m just about to set off on a 7 mile run. It’ll take me just over an hour, so I’m going to take the hypotonic juice with me. It’s not too hot, I won’t be running fast, so water with a bit of sugar in it should be adequate.

I hope!

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