* Hypotonic drinks are dilute carbohydrate electrolyte solutions which are less concentrated than body fluids and are therefore rapidly absorbed by the body. They begin the rehydration process while simultaneously helping to replenish carbohydrate energy reserves. No proprietary versions of such drinks are currently available on the UK market since an Umbro product was withdrawn;
* Isotonic drinks have a similar carbohydrate electrolyte concentration to the body's own fluids. They are best used later in the recovery process to boost energy intake while still encouraging fluid uptake during the final stages of rehydration. Proprietary brands include Liquid Power, Isostar and Lucozade Sport;
* Hypertonic drinks are solutions with a higher carbohydrate electrolyte concentration than body fluids. In general these types of drinks contain large amounts of carbohydrate and are therefore best used as energy supplements during periods of heavy training, when energy expenditure is likely to be high. Again, no proprietary versions are available in the UK, although you can make an isotonic drink hypertonic by making it up in a more concentrated form. If you prefer to drink water alone after exercise, it is possible to achieve adequate rehydration if solid food which replaces lost electrolytes is consumed at the same time. If this is not possible, some form of electrolyte solution is essential.
This does not mean you should never drink water after exercise - just that you need to take account of your levels of fluid and electrolyte losses. Where losses are high and large volumes of fluid need to be consumed in a short period, it is important to consume sodium in combination with fluids if fluid balance is to be achieved and maintained.
