Electrolytes serve three general functions in the body:
- many are essential minerals
- they control osmosis of water between body compartments
- they help maintain the acid-base balance required for normal cellular activities
The sweat that evaporates from the skin contains a variety of electrolytes. The electrolyte composition of sweat is variable but comprises of the following components:
- Sodium
- Potassium
- Calcium
- Magnesium
- Chloride
- Bicarbonate
- Phosphate
- Sulphate
A litre of sweat typically contains 0.02g Calcium, 0.05g Magnesium, 1.15g Sodium, 0.23g Potassium and 1.48g Chloride. This composition will vary from person to person.
Glucose
Carbohydrate is stored as glucose in the liver and muscles and is the most efficient source of energy as it requires less oxygen to be burnt than either protein or fat. The normal body stores of carbohydrate in a typical athlete are:
- 70kg male athlete - Liver glycogen 90g and muscle glycogen 400g
- 60kg female athlete - Liver glycogen 70g and muscle glycogen 300g
During hard exercise, carbohydrate can be depleted at a rate of 3-4 grams per minute. If this is sustained for 2 hours or more, a very large fraction of the total body carbohydrate stores will be exhausted and if not checked will result in reduced performance.
Recovery of the muscle and liver glycogen stores after exercise will normally require 24-48 hours for complete recovery.
During exercise, there is in an increased uptake of blood glucose by the muscles and to prevent blood glucose levels falling the liver produces glucose from the liver stores and lactate.
Consuming carbohydrate before, during and after exercise will help prevent blood glucose levels falling too low and help maintain the body's glycogen stores. Many athletes cannot consume food before or during exercise and therefore a formulated drink that will provide carbohydrate is required.
Isotonic - quickly replaces fluids lost by sweating and supplies a boost of carbohydrate. This drink is the choice for most athletes - middle and long distance running or team sports. Glucose is the body's preferred source of energy therefore it may be appropriate to consume Isotonic drinks where the carbohydrate source is glucose in a concentration of 6% to 8%.