Sports drinks are mild carbohydrate-electrolyte solutions, designed to keep bodies well- hydrated and fueled during exercise of longer than 45 minutes. Drinking fluids during exercise also reduces the increase in body temperature and the amount of stress on the cardiovascular system, especially important when exercising in hot environments.
Sports drinks offer approximately 14-20 grams of carbohydrate per 250 ml (8 ounces). This carbohydrate level (approximately 6-8 % carbohydrate in solution), delivers the optimal amount of both energy and fluid to enhance performance during exercise. The carbohydrates can come in many different forms: sucrose, glucose, fructose and glucose polymers. Sports drinks that contain mostly fructose may slow absorption down and cause stomach cramps because fructose is absorbed by passive diffusion in the gut.
What to look for:
sports drinks with higher percentages of the fast absorbing carbohydrates;
glucose, sucrose and glucose polymers (malto dextrins);
6-8 % carbohydrate in solution;
14-20 grams of carbohydrate per 250 ml;
approximately 100 mg sodium per 250 ml (8 ounces).
For training sessions of more than 45 minutes sip continually on sport drinks throughout your exercise session. 4-6 ounces every 10-15 minutes during exercise are fluid guidelines to help maintain hydration status. The hotter and more humid it is the more you will need to drink. The primary purpose of drinking a carbohydrate solution rather than plain water is to maintain a sufficient concentration of blood glucose and to sustain a high rate of energy production from blood glucose and muscle glycogen. Ultimately, this will allow longer exercise duration and the ability to increase the intensity (sprint!) at the end of the exercise bout. The key to choosing a sports drink is to select the one you find most palatable. If you like the taste of it, you’re likely to drink more of it and stay better hydrated than you would on plain water.
There are three types of Sports Drinks all of which contain various levels of fluid, electrolytes and carbohydrate.
Isotonic Fluid, electrolytes and 6-8% carbohydrate
Hypotonic Fluids, electrolytes and a low level of carbohydrate
Hypertonic High level of carbohydrate
The osmolality of a fluid is a measure of the number of particles in a solution. In a drink these particles will comprise of carbohydrate, electrolytes, sweeteners and preservatives.
In blood plasma the particles will comprise of sodium, proteins and glucose. Blood has an osmolality of 280-330mOsm/kg. Drinks with an osmolality of 270-330mOsm/kg are said to be in balance with the body’s fluid and are called Isotonic. Hypotonic fluids have fewer particles than blood and Hypertonic have more particles than blood.
Consuming fluids with a low osmolality, e.g. water, results in a fall in the blood plasma osmolality and reduces the drive to drink well before sufficient fluid has been consumed to replace losses.
Which is most suitable?
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% – e.g. High Five, SiS Go, Boots Isotonic, Lucozade Sport.
Hypotonic – quickly replaces fluids lost by sweating . Suitable for athletes who need fluid without the boost of carbohydrate – jockeys and gymnasts.
Hypertonic – used to supplement daily carbohydrate intake normally after exercise to top up muscle glycogen stores. In ultra distance events high levels of energy are required and Hypertonic drinks can be taken during exercise to meet the energy requirements. If used during exercise Hypertonic drinks need to be used in conjunction with Isotonic drinks to replace fluids.