Sports Drinks: Hypo, ISO, Hyper-Tonic

Avatar for Hadyn Luke Hadyn Luke posted this on Monday 3rd of September 2012 Hadyn Luke 03/09/2012


Sports Drinks: Hypo, ISO, Hyper-Tonic

Sports drinks are commercially marketed as performance-based drinks. A personal trainer would normally recommend sports drinks as a way of replenishing water during a training session as well as carbohydrates and electrolytes.

If a client is exercising for less than 60 minutes, they should only need to replenish water. If the workout is increased to between one and three hours, they will need to replenish both water and carbohydrates. For a period of more than three hours, for example a marathon, they will need to replenish electrolytes as well as water and carbohydrates.

Common sports drinks

The three most commonly available sports drinks are:

  1. Hypotonic (0-4% carbohydrate)
  2. Isotonic (4-8% carbohydrate)
  3. Hypertonic (8%+ carbohydrate)

The grading relates to the sports drink’s levels of carbohydrates, electrolytes and sodium/potassium particles. If these are lower than those in the blood, the drink is classed as hypotonic; if they are higher, it’s classed as hypertonic; and if they’re the same, it’s an isotonic drink. As all three contain both water and sugar, they will all rehydrate and replenish energy.

Hypotonic drinks are rarely used, as clients can get the same benefit from an isotonic drink without any additional issues. Hypertonic drinks can be linked to gastro-intestinal discomfort, causing stitches, nausea or sickness. For this reason, isotonic sports drinks are the most popular.

Calculating the carbohydrate percentage of a sports drink

Different sports drinks can vary quite considerably in content. If a personal trainer wants to calculate the carbohydrate percentage of a sports drink, they should divide the number of carbohydrates listed on the label by the amount of fluid in the bottle and then multiply by 100. For example, a 1 litre (1,000ml) bottle of fluid with 60g of sugar would contain 6% carbohydrate concentration ([60/1000] x 100 = 6%).

Making your own sports drink

A personal trainer can also show a client how to make their own sports drink. One option is to use a cordial drink containing sugar (rather than the no-sugar varieties). If you check the sugar content listed on the label and work out its percentage value within the drink, you can then add the appropriate amount of cordial to water. For example, with a cordial that has 25g of sugar in 25ml, if you add 50ml of that to a litre of fluid, you will have a 5% isotonic sports drink. Alternatively, mixing a litre of water with a litre of fresh orange juice (not from concentrate) would normally equate to a good percentage sports drink.

The main benefits of mixing your own sports drink are: first of all, it usually works out cheaper, and second, the drink is likely to have fewer of the additives and preservatives that are often used in sports drinks.

Why are sports drinks effective?

The reason that sports drinks are so effective is that your body will actively absorb sugar, whereas it won’t actively absorb water. For every sugar molecule that your body absorbs, it will absorb two molecules of water. So whether the goal is hydration or energy replacement, a sports drink should have the desired effect.

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