Water constitutes 60% of male body weight and 55% of female body weight and is eliminated through perspiration, defecation, and urination - consequently the levels in the body need to be replenished constantly.

An average adult needs to consume approximately 2.5 litres of water per day, a figure that increases during exercise. Sweating is the way in which the body maintains its core temperature of 37C but this will result in the loss of body fluid and electrolytes like chloride, calcium, phosphate, magnesium, sodium and potassium. If the levels of electrolyte are not checked and replenished then, potentially, this can lead to dehydration followed eventually by circulatory collapse and heat stroke if the percentage body weight lost as sweat exceeds 10% or more.

Historically, water was always the preferred choice for remaining hydrated throughout any endurance exercise, but it causes bloating and stimulates urine output - thereby making it inefficiently retained.

An isotonic or sports drink has the benefit of possessing electrolytes, which aid fluid absorption, and carbohydrates that provide the necessary fuel for the body to maintain peak performance and enhance post exercise recovery.

Carbohydrate is stored as glucose in the liver and muscle, it is the most efficient source of energy as it requires less oxygen to be burnt that either protein or fat. During a period of exercise, the muscles increase the uptake of blood glucose, which the liver produces from its stores, to prevent the levels from falling.The carbohydrate stores of the body are depleted gradually and if they are not restocked will result in a reduced performance.

Hence, consuming carbohydrate before and after exercise will prevent blood glucose levels from dropping too low and maintain the body’s glycogen stores.

The higher the level of carbohydrate in a drink, the slower the rate at which the stomach empties, Isotonic drinks with a carbohydrate level of 8% will be disposed from the stomach at a rate similar to that of water.

Electrolytes like sodium that are also present in the drink will reduce the urine output, enabling the fluid to be quickly emptied from the stomach - promoting the absorption from the intestine and encouraging fluid retention.

During extreme endurance activities such as marathons, it is important that competitors drink beverages containing sodium electrolytes to avoid the potentially life threatening condition known as hyponatremia (a low blood sodium level).

A good rule of thumb is to choose sports drinks over water if you plan to participate in 45 minutes or more of high-intensity activity. It’s important to drink before, during and after activity. You should drink one hour before a workout to give your kidneys time to dispose of excess fluid. And if possible, you should consume every 15 to 20 minutes during a workout. Most importantly, drink enough afterwards to replace all losses within the first two hours. The extra ingredients in a sports drink will more successfully refuel your body after that long run. The longer the activity, the more important sports drinks become.