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April 2017
Fitness and sport
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Pre-competition diets

When doing physical activity, we slowly use up our stored glycogen which is present in the muscles and liver (around 40g in total and in the muscles, 2g/100g of muscle tissue). Even after just one hour of a competition, stored muscle glycogen can be reduced by 50%. Furthermore, the speed at which the glycogen is metabolised depends on the power we are exerting, and if an individual uses the anaerobic paths even just partially, glycogen is used up 18 times quicker than if only the aerobic paths were used. Therefore, we do actually pay for exerting more power by ‘running off an empty tank’. This is the main reason why, at a certain point, you cannot run anymore in long distance, aerobic events therefore, you must increase the glycogen stores before a competition.

Pre-competition meal (the evening before the competition)increase the calories that come from carbohydrates by 75% (normally 50-55%)

This increase is strengthened if, some days before the competition, you carry out a training method which uses up the stored glycogen as this stimulates a more accentuated synthesis of glycogen (a condition called ‘supercompensation’). By doing this, you can increase the normal amount of stored glycogen by 20-40%.

However, because we eat dinner in the evening, the question arises about whether there is enough time to partially break down the glycogen. Some data shows that fasting for 6-12 hours can cause muscle glycogen to be used up quicker therefore it is recommended that, during the 6 hours before the race, you eat a light dish (containing no fats) containing 70-100g of carbohydrates. It is interesting to think about the source of the carbohydrates oxidised by the muscles during a long period of exercise (for example, cycling for 4 hours and working at power equal to 70% of our maximum power): the percentage of carbohydrates coming from muscle glycogen reduces gradually and is practically annulled after 4 hours. This reduction is compensated by a progressive increase in the glucose taken on by the blood and which comes from the glycogen stored in the liver.

The dissociated diet
This idea was put forward a few years ago with varying success. The most recent variation of this diet involves the athlete carrying out fairly intense training the week before the competition to diminish glycogen stores. By doing this, the resynthesis of glycogen is stimulated per se, however, the principle of the diet is to not satisfy this tendency, but instead starve the muscles further so as to greatly reduce the sugar supply for a few days. Then, three days before the competition, you load up on glucose. 
This diet is not easily tolerated and the pre-competition diet is currently the preferred choice.

Replenishment during a competition

The ‘ideal’ drink to drink when competing will have a glucose content of 4-8% and 600-1200ml should be drunk every hour (the actual amount depends on how much you sweat). This allows carbohydrates to be absorbed at a rate of 30-60g per hour. Fructose is not recommended as this sugar must first be converted to glucose before it can be absorbed, therefore absorption and the time it takes to get to the muscles takes 5 times longer.

Replenishment of carbohydrates after a competition

After a long and tiring competition you need to start consuming carbohydrates fairly quickly and the recommended amount is 50-75g every two hours. Drinks rich in sugar are recommended after a competition to replenish stocks. If you consume enough carbohydrates, stocks can be replenished at a rate of 5% per hour therefore it takes a total of 20 hours to fully replenish glycogen stocks. The speed of resynthesis varies amongst individuals and definitely diminishes with age.


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