How often do you see people in gyms, pre race or even at work (?!?!?!?) reach for their bottles of isotonic sports drinks and guzzle them down. I wonder how many of them actually need an isotonic drink for the exercise session they are about to do, or even understand why an isotonic drink actually is actually called ‘an isotonic drink’?

So, why is an isotonic drink called ‘an isotonic drink’?

Osmolality is an index referring to the number of particles present in a solution. Blood plasma has an osmolality (or tonicity) of around 280 – 300 mOsm/kg. Drinks with a tonicity of 270 – 330 mOsm/kg are classified as being in balance with the body’s own fluids and are referred to as isotonic. These products provide a faster rate of absorption and contain the necessary electrolytes lost through increased sweating during intensive exertion. The tonicity of Lucozade Sport for example is 280 mOsm/kg, making it compatible with that of blood.

Next time you reach for an isotonic sports drink, just pause for a second and ask yourself, do I really need this for the session I am about to do?

Isotonic drinks should only be taken during exercise or competition if the session is longer than a hour, certainly if a race is longer than 90 mins or if a pre-exercise meal is not possible (such as early morning intensive training). If an adequate pre exercise/ race meal has been consumed, there is really no need to take an isotonic sports drink on board as carbohydrate (glycogen) stores should be sufficient for the mean time. If you feel the need to drink something, why not sip on good old H20, at least this way you’ll keep yourself hydrated for the session or race ahead.

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