The human body contains about 70% water. A reduction in body water will cause a reduced efficiency in cellular function. Soccer players have been shown to lose 1-5% of body weight through sweating (up to 4.5 kg in hot humid conditions) which results in impaired performance. Controlled studies show that a reduction of one percent in body weight can result in a ten percent reduction in work capacity (although individuals do show differences in body mass loss as some may have a better thermoregulatory capacity).
Furthermore, evidence shows that body mass loss will also cause mental functions to deteriorate perhaps resulting in players making mistakes. It is therefore important that any sweat loss is adequately and promptly replaced through fluid intake, whether this be through water or sports drinks. Figure 1 gives a general idea of how increased body water loss reduces performance capacity.
Dehydration will have a more immediate effect when playing or training in hot humid environments. Fluid replacement is extremely important to ensure players do not become dehydrated and to prevent any risk of heat injury. Weighing players before and after performance may be useful to evaluate weight loss. Thirst is never an adequate indicator of the physiological state of dehydration. Players should always be encouraged to drink more than their thirst indicates. Thus, correct fluid intake practice is extremely important.
Water has been shown not only to be useful in preventing dehydration. A scientific study demonstrated that it can actually help improve sprinting capacity in the second half of matches when compared to players who did not drink any water. Water is extremely useful in preventing dehydration, especially in hot conditions and is an excellent replacement fluid (In hot conditions, it is more important to rehydrate the player than to provide additional energy). For every 1 kg decrease in body weight - replace with 1 litre of fluid. A player's urine should be a diluted, pale colour. If it looks deep yellow, he should drink more. However, the consensus view is that a sports drink which contains an energy source in the form of carbohydrates along with electrolytes is more effective in maintaining performance.
Drinking carbohydrate solutions and commercial sports drinks have been shown to aid rehydration and improve playing performance. Carbohydrate (CHO) ingestion may improve performance by slowing the onset of fatigue through the sparing of muscle glycogen utilisation by increasing blood glucose levels (the primary aim), promoting muscle glycogen resynthesis and increasing post-match recovery. This is especially useful if extra-time occurs and when regular matches limit the time available for fully restoring glycogen stores (can be up to to 20 hours). For example, players who consumed CHO solution before a match and at half-time covered greater distances in the second half than those who did not.
The ideal sports drink should have 5 major qualities:
1 - Tastes
When consuming CHO drinks, many factors need to be taken into account: type and concentration of CHO of used, when to drink and the weather conditions. Fluid absorption is influenced by the the quantity, temperature and sugar content of the fluid. For example, warmer drinks are absorbed slower than colder drinks but the latter may cause stomach discomfort. Gastric emptying is maximised when the amount of fluid in the stomach is high. The concentration of sugar is however, the most important constituent. The greater the concentration, the slower the rate it can be emptied from the stomach. However, so-called sugar polymers (e.g. maltodextrin) seem to be absorbed faster at a similar concentration compared to normal sugars.
So how much CHO needs to be ingested ? Scientific studies have shown that to restore and maintain blood glucose levels in late exercise to delay fatigue by around 45 minutes, 60 grams of CHO per hour are needed. To consume 60g/h of CHO, it is possible in several ways:
a 20% solution - too concentrated and reduces fluid uptake
It seems that by drinking relatively large volumes of 5-15% CHO solutions, then the athletes can obtain both their CHO and fluid needs. Evidence shows that players who drank 500ml of a 7% glucose solution 15 mins before a game and at half-time had significantly less glycogen depletion. This might lead one to think that increasing the concentration would be better but as mentioned earlier emptying from the stomach will be slower. It is important to define these different concentrations:
Hypotonic Drinks: Are weaker concentrations of sugar and electrolytes (sodium and potassium) per 100mls than the body's own fluids. May be absorbed faster than plain water and are useful in hot conditions.
Isotonic Drinks: same concentration of sugar and electrolytes as the body's fluids per 100mls. May be absorbed as fast or faster than plain water. These drinks provide the ideal compromise between rehydration and refuelling and are useful most of the time.
Hypertonic Drinks: contain higher concentrations of sugar and electrolytes per 100mls than the body's own fluids. Are absorbed more slowly than plain water. They are useful during ultra-endurance events and are generally not needed for soccer.
Players regularly lose 2.5 litres of body fluid and can use between 21-90% of their muscle glycogen during a match and should therefore consume CHO drinks but at what intervals ? Firstly, on a hot day, the fluid CHO concentration should not be more than 5% and a larger amount of fluid is best consumed whereas on a cold wet day, one can increase the CHO concentration to around 10% but reduce the volume of fluid ingested. Alcohol and caffeine drinks (coffee and tea) should be avoided around competition.
Pre-match: Firstly, it is important that players are well hydrated before a match and they may begin the process of toping up with fluid the day before. For example, an extra litre of fruit juice may be drunk the evening before. On match day, players should have plenty to drink and be encouraged to drink even when they are not thirsty. Ideally, a player should drink around 250- 500mls of fluid 2 hours before kick-off (such a practice should optimise hydration while allowing enough time for any excess fluid to be excreted as urine before the game starts), and 200 ml of a 3-10% concentrated solution immediately before the match.
However, it is advisable that a player should not drink a concentrated sugar solution 1 hour before training or competition as this will stimulate insulin leading to a reduction in blood sugar and may lead to hypoglycaemia. It can also decrease the availability of body fat causing the player to rely on muscle glycogen and lead to a more rapid onset of fatigue due to an earlier loss of this latter energy source.
During a match: Try to drink small amounts of fluid at regular intervals, say every 15 minutes (although this is not always possible) and always at half-time. Try 200 - 300 ml of a 3-10 % sugar concentration. This will replenish a significant amount of lost water and help satisfy the body's demand for sugar.
Post-match: After exercise, the major considerations are to replenish CHO and fluid losses. The athlete should immediately drink adequate fluids to replace sweat losses during exercise. Avoid alcohol and caffeine as this may prevent rehydration. Drink at least 500mls of water or a can of an isotonic sports drink (helps refuelling and rehydration) immediately after the match and continue drinking at regular intervals, until you have matched your body weight losses through sweat.
A player may want to try to make their own drinks as commercial products may be too expensive or not contain the right proportions of CHO. For example, a player who would like a 5% CHO concentration can add 50 grams of sugar to a litre of water along with flavouring such as lemon juice. Fizzy soda drinks are not recommended due to their high sugar content and the possibility of causing stomach discomfort.
Never try new drinking strategies out on the day of a match. There are large inter-individual differences in the ability to tolerate drinks. Some players may not be able to benefit from drinking large amounts of fluids and will suffer from stomach discomfort. Only try out different drinking habits during training.
There appears to be little physiologic need to replace electrolytes during a single exercise session of moderate duration (e.g., less than three to four hours), particularly if sodium was present in the previous meal. The need for supplementary electrolytes such as sodium/potassium or magnesium during match play is also debatable; after matches, a couple of well balanced meals will restore the post match levels. A commercial sports drink may also supply the required electrolytes.
1 - Drink
plenty or increased amounts of fluid the day before and on match day.
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