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Rehydration for Sport
The importance of water

Water makes up between 40-70% of total body mass. Those with lean, muscular bodies have higher water content than those with the same body mass who carry more fat, as fat contains less water. The human body does not store water and if water loss is high, the body will become dehydrated and death will occur in a matter of days.

Water plays an essential role in the biological functioning of the human body. Under typical conditions, the body will maintain a balance between fluid intake and output and feelings of thirst indicates the body's requirement for water.

Water is crucial for maintaining and regulating body temperature and assist by absorbing heat and cooling the body through evaporation (sweating).
Water is a component of body cells and tissue fluid and is a transport mechanism for vital substances such as blood plasma.
Water is an excellent medium for the exchange of oxygen, nutrients and waste products between cells and blood.
Water facilitates excretion of waste products in the form of urine and faeces.
Dehydration during exercise

Up to 100 times more heat is produced by contracting muscles during exercise and the body must react to this change by regulating the body temperature before it reaches a dangerous level.

The heat is transported to the skin surface by blood, where it is then lost through convection, radiation and evaporation (sweating). During periods of hot weather, little or no heat is lost through convection or radiation and therefore increased sweating occurs.

As fluid loss increases through periods of profuse sweating, the body becomes increasingly dehydrated. Water is lost from all areas of the body and a reduction in blood volume will result. As there is a reduction in blood for the heart to pump around the body, cardiac output is reduced, which in turn reduces the delivery of oxygen and vital nutrients to the contracting muscles. The circulatory system tries to compensate by constricting blood vessels and reducing blood flow to the skin, therefore less heat is lost and the body temperature rises.

Symptoms of dehydration include:

Limited performance
Complete exhaustion and collapse

Performers are recommended to take the following precautions to prevent dehydration:

Drink plenty of water the day before the event/ prolonged activity
Drink two-three cups of water approximately two hours before the event
Drink one cup of water approximately 15-30 minutes before the event
Drink half a cup of water every 15-20 minutes during the event (if the event lasts over 30 minutes)

An effective way of determining dehydration levels, record the performer's weight before and after the event. For every 1kg of weight lost, 1 litre of water should be consumed to restore the water balance.

Sports Drinks

Sports drinks are being continually developed to speed up the rehydration process. Such drinks contain sodium and /or carbohydrates (glucose), amongst other electrolytes. Many of these drinks contain a glucose polymer, which is an easily digestible form of complex carbohydrate.

Research indicates that sports drinks are required in addition to water if the athlete is intending to perform at low-high intensity for more than one hour. Water is perfectly adequate for any shorter periods as the glucose provided by a sports drink will not be utilized and sodium can easily be replenished through diet.

Athletes performing at a higher intensity for longer periods can benefit from sports drinks as they rehydrate faster and if consumed during exercise, may enhance performance. The glucose content of the sports drink raises blood sugar levels and spares muscles glycogen, so the muscles are able to contract harder, for longer periods. Sodium assists in the retention of water in the blood without inhibiting feelings of thirst therefore hydration is faster.

It should be noted that further research by nutritionists warn that too much sodium may be detrimental and that sports drinks can be high in calorie content.

There are three types of sports drinks that are differentiated by their rate of absorption. Each type of drink will have a different osmolarity. A drink with a high osmolarity will have more particles in solution than a drink with low osmolarity.

Hypotonic drinks have low osmolarity and typically contain approximately less than 4 grams of sugar per 100 ml. They are designed for rapid rehydration and are aimed at the low/moderate, short period (up to one hour) athlete.

Isotonic drinks are absorbed at about the same rate as water and contain between 4-8grams of sugar per 100 ml. This type of drink is aimed at endurance athletes performing between one and three hours.

Benetthrope info@backontrack-physiotherapy.co.uk