What's the difference between hypertonic and isotonic sports drinks?  Which one is better?


Tonicity is a measure of osmotic pressure, or in very non science terms, it tells us how much solid type stuff (solutes) are in a liquid.  Hypertonic means there is a greater tonicity than the control subject, isotonic tells us its equal to the control and hypotonic means there is less than tonicity or osmotic pressure than the control.


The ‘control' is whatever we're comparing tonicity.  For example, blood has an osmotic pressure of 7.65atm at 37.5degrees, so anything the same as this is isotonic.


And this is where sports drinks come in.


•·         Isotonic sports drinks provide around 6%-8% CHO and sodium (typically).  This makes it the closest "formula" to your blood and is thought to provide the most rapid absorption.  But note, if you eat a CHO or gel or even drink water along with your Isotonic sports drink the entire ingestion will be either hypertonic or hypotonic.  So when practicing your sports nutrition, try just having your isotonic sports drink on its own to see if the rapid absorption produces better results for you.

•·         Hypotonic sports drinks provide less than 6%-8% CHO and sodium, so is a little better for those wanting a lower sugar hit or who may already be taking an electrolyte supplement.  Some athletes perform better on a hypotonic solution than an isotonic, so have a play around with the different tonicities and see what feels better for you.  Wapnir & Lifshitz  suggest, with good evidence that hypotonic solutions provide the most rapid hydration.

•·         Hypertonic sports drinks provide greater than 8% of CHO and sodium, and is greater than the ratio your blood is carrying.  This ratio makes the fluids from the drink slower to absorb, but good for long term replenishment of carbs and sodium.  If you need a quick hit of carb or sodium,  isotonic may be the better choice for you.  But again, each athlete is different.  If you are quite dehydrated the rate of absorption of a Hypertonic sports drink may not be fast enough for you and make your dehydration more severe.


If you're trying to lose weight or just doing your daily hour at the gym you don't need a sports drink.  And if you've got a good balanced diet, even a 2 hour gym session doesn't require a sports drink.


In a nutshell, it basically means how much sugar and sodium is in your water.  Each athlete is different, and different conditions may require a different formulation.  For example you may do well on a hypertonic drink doing a marathon in winter, but an ultra-marathon in summer can dehydrate you quickly, so an iso or hypo tonic solution may be best for rapid fluid absorption.


Whatever you decide to use, keep rule number one firmly in mind:

If you haven't practiced it first....don't do it on the day.

Stacey Hancock
23 May 11

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