The most popular of all the, er, ‘tonics’, isotonic drinks (or energy drinks) have a similar concentration of dissolved particles to the body’s own fluids. This means that the amount carbohydrates in these drinks – in the form of glucose, sucrose or fructose – will be mixed with the fluid at a ratio similar to a biological one.

Therefore isotonic drinks are easily absorbed, replacing fluids and giving a carbohydrate boost relatively quickly. The depletion of muscle carbohydrates, along with dehydration, is the primary source of fatigue when exercising.

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Most will be mixed at a concentration of six to eight percent. This is because research consistently finds that glucose polymer drinks (aka sports drinks) mixed to a 6-8% solution are optimal in terms of absorption of energy and fluid from the drink.

It’s possible to make your own budget beverage by mixing squash with water and a pinch of salt.

The only problem is that more glucose can effect the ’emptying time’ from the stomach to the small intestine, causing gastrointestinal symptoms. If you have problems with stomach cramps, nausea, flatulence or indigestion on the bike, you might want to consider a lower concentration of sports drink (see hypotonic drinks below). Fructose-based drinks have also been implicated in gastrointestinal issues, so avoid those if you are easily irritated.

Also remember that consuming caffeine effects your absorption of carbohydrates too.

Riding for over an hour? You’ll want to consume 30-60g of carbohydrate an hour to maintain optimum pace and stave off fatigue. You can, of course, find this carbohydrate from real foods if you prefer, and it’s possible to make your own budget beverage by mixing squash with water and a pinch of salt.

What about these 2:1 drinks?

An excellent question. The isotonic bracket also includes varieties of 2:1 sports drinks. 2:1 is the ratio of glucose to fructose in the drink (with added electrolytes, of course).

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These drinks aim to up the rate of your carb absorption: it’s all well and good taking in loads of carbohydrates but if your body can only manage to process 60g per hour, an extra 30g won’t make any difference to performance.

Some research shows that the magic 2:1 ratio enables you to absorb more carbs, more quickly – up to 90g in an hour. There’s a bit of disagreement as to whether this is actually more than what is optimum for performance benefits, but research seems to show that these 2:1 drinks do make a difference for endurance athletes.

Try these…

Lucozade Sport, High5 Energy Source, Gatorade Perform, Powerade, Torq Energy