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Tuesday, September 17, 2019

Nutrition and Sports


One of the most frequent recommendations in medicine is to carry out the physical exercise in a moderate way due to the beneficial effects it has on the body.

The athlete's diet should consider the individual nutritional needs of combustible and structural material, as well as regulatory elements depending on age, sex and the type of physical activity developed.

Among the oldest myths related to the nutrition of athletes, is that of consubstantiality, according to which the ingestion of large amounts of protein-rich foods was recommended to replenish muscle mass, which was supposedly consumed during exercise. Another nutritional myth is the massive consumption of pills, powders, and potions rich in vitamins, to enhance the efficiency in obtaining energy by the body from food.

Some common mistakes among athletes are low food intake before a competition, to reach a certain weight, or excessive food consumption, to ensure a greater reserve of combustible material for exercise. Another frequent mistake is the ingestion of hyperosmotic solutions with electrolytes or sugars that, instead of favoring rehydration, lead to a reduction in water reserves.

Pre-exercise feeding

In sports with a predominance of aerobic work, glucose and glycogen are essential for muscle metabolism when an exercise develops with a moderate to the strong intensity and lasts for more than 75-90 minutes. That is why it is important to instill in the athlete the idea that a diet with fewer carbohydrates than is advisable may be the origin of early fatigue; Because when it comes to an aerobic endurance exercise, fatigue usually appears as a result of a depletion of muscle glycogen or hypoglycemia.

A few days before a aerobic competition, such as a marathon or a triathlon, it is convenient for the athlete to regulate their diet and training in an attempt to maximize ("overcompensate") glycogen stores. A practical method to achieve this is to implement a tapering, that is, a modification of the training, so that in the seven days before the competition the volume is significantly decreased, in a progressive way, maintaining high training intensity. During the days –7, -6, -5 and –4 a low carb diet is followed. This will cause the muscle to be partially depleted in its glycogen stores and ready to overcompensate. During the three days before the competition, the diet has to be rich in carbohydrates,

However, eating this amount of food can be accompanied in some people with minor gastrointestinal symptoms such as a feeling of fullness and discomfort. Therefore, studies carried out by Lamb and Snyder 1 (1991) suggest replacing part of these complex carbohydrates with beverages rich in maltodextrin, low in waste and very energetic, as a method as effective as the diets commonly used to "recharge" the muscle.

Precompetitive food, a meal rich in carbohydrates taken in the hours before the competition, can complete liver and muscle glycogen stores. The liver, responsible for maintaining plasma glucose levels, requires frequent meals to preserve its small glycogen reserve. Those athletes who follow a fast in the previous 6-12 hours, and do not consume carbohydrates during the competition are more likely to develop hypoglycemia during it.

A meal that mixes carbohydrates of fast, intermediate and slow assimilation is preferable. In the previous hour, it is highly recommended that all food is in liquid form.

The recommendations made by different committees of nutrition experts on a person's daily protein needs are in a range between 0.8 and 1.2 g / kg / d, but it is not resolved if these recommendations are sufficient. For an athlete. For Butterfield and Calloway2 (1984), these amounts are sufficient for people who perform low-intensity aerobic physical activity, such as walking; However, athletes who usually work with higher intensities need more protein in their diet.

In most cases, enough protein can be obtained from the daily diet. However, in some circumstances, it may be advantageous to use protein supplements, especially since they contain very little fat, purines or cholesterol.

On the one hand, the exercise of force can produce a considerable glycogenolytic effect. And it has been seen that a significant reduction in muscle glycogen concentration is associated with fatigue and decreased strength. Some studies suggest that carbohydrate intake immediately before and during an exercise of these characteristics can improve physical performance, can accelerate the recovery of muscle glycogen after strength exercise and can optimize protein synthesis and muscle hypertrophy.



Most sports dietitians argue that it is not necessary to supplement the diet with proteins and/or amino acids and that an adequate calorie diet, which provides 15% of these in the form of proteins, is sufficient to meet the needs of the athlete.
1 Lamb DR, Zinder Ac. "Muscle glycogen loading with a liquid carbohydrate supplement". Int J Sport Nutr 1991; 1: 52-60

Food during physical exercise

Holloszy and Kohrt3 (1996) point out that it is possible to cover long distances working at a high average intensity, without depleting the glycogen muscle reserves, by taking a fast-assimilating carbohydrate supplement, regardless of whether they are taken in solid or liquid form. During brief periods of rest, or during periods when the intensity of exercise drops sufficiently, rapid synthesis of a certain amount of glycogen can occur in muscle fibers with a low glycogen concentration and not active in that type of exercise.
3 Holloszy JO, Kohrt WM. "

Post-exercise exercise

The rapid recovery of glycogen stores after a training session or competition is essential if you want to maintain optimal performance in successive training sessions or very followed competitions. However, the speed with which the muscle can recover its glycogen stores will be closely related to three dietary factors: the time elapsed between the end of physical exercise and the beginning of carbohydrate intake, the type of carbohydrate chosen and the amount ingested

Some studies compiled by Friedman et al.4 (1991) estimate that administering a hydrate supplement every two hours, taking the first dose in the first 15 minutes after the end of the exercise, optimizes the glycogen resynthesis rate. Also, the intake of a supplement that mixes carbohydrates and proteins is accompanied by a faster recovery of glycogen stores because higher plasma insulin levels are promoted.


On the other hand, Lamb et al.5 (1990) provide data that support the existence of a limit on the intake of these carbohydrates, with a range that would range between 500 and 600 g / d, above which there is no observed increased glycogen storage or an improvement in physical performance.

In short, from a practical point of view, after a physical exercise, that athlete should immediately start drinking between 1.5 to 2 liters of water in which they have dissolved, for example, 50-70 grams of glucose or maltodextrin /liter. Between 1.5 and 2 hours later, you should take a meal containing, for example, a cold salad to which rice, or cooked potato, or peas is added. Also, a dish that combines meat and rice or mashed potatoes. It is also advisable to include foods such as fruit yogurt, rice pudding, banana, fruit juices, raisins; and the energy drink with the concentration of carbohydrates already described, which will have to continue to be consumed during subsequent hours until a total of 500 to 600 grams of carbohydrates is completed.

However, Coyle6 (1992) points out that when for various reasons a person cannot eat and/or drink carbohydrates frequently (every two hours), the last meal should provide the number of carbohydrates equivalent to the period of time that will be without feeding Costill et al.7 (1981) find that glycogen synthesis is similar when two large meals are taken compared to seven smaller meals. However, if a person decides to eat only twice a day, he must be aware that each of them will contain a large amount of food if only foods such as legumes, potatoes, rice, pasta, cereals, etc. are ingested. Therefore, in this case, it is necessary to drink solutions with carbohydrate concentrates.

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