Nutrition For Training

The training load of athletes varies greatly between individuals, depending on the nature of the sport and the level of competition, and it also varies over time in relation to the competitive season. Training may consist of high-intensity resistance training, brief but intense sprints, prolonged moderate intensity efforts, or technical work. Each places different demands on the muscles, cardiovascular system, and other tissues, and each has different energy requirements. The aim of training is to induce changes in body tissues and organs that will improve exercise performance, but different adaptations are required in different sports. Increasing muscle mass, strength, and power is a key objective in many sports, but in other sports, these changes would hinder, rather than help, performance. The training stimulus, therefore, must be specific to the objectives of the event. 

Within limits, the greater the training stimulus – consisting of the intensity, duration and frequency of individual training sessions – the greater the adaptation that takes place. As mentioned above, nutrition is important in promoting recovery between training sessions to allow an increase in the training load that can be sustained without succumbing to illness and injury, and also in allowing more effective adaptations to each bout of training. This may be important in complex sports such as soccer, where different training objectives must be achieved and where the training must also accommodate practice of a variety of skills.

Influence of Exercise Training on Energy Balance Energy must be supplied by the diet to meet immediate energy needs (body functions, energy for activity, and growth) and for the maintenance of body energy stores. Energy stores, consisting primarily of fat, but including the key carbohydrate stores in liver and muscle, play a number of important roles related to exercise performance, since they contribute to size and function (e.g., muscle mass) as well as providing fuel for exercise. Athletes try to manipulate these factors towards the characteristics that offer advantages to their sport: this may mean a change in body mass, a change (usually a reduction) in body fat, a change (usually an increase) in muscle mass, and optimization of muscle and liver carbohydrate stores.

Not all athletes are able to correctly identify goals that are suitable for their sport and for their individual make-up. This can lead to various problems, including excessive restriction of energy intake in an attempt to achieve an unrealistically low body mass. If energy intake is too low, and especially if carbohydrate intake is inadequate, it may not be possible to sustain the training load without the risk of chronic fatigue, injury and illness. If an energy deficit is incurred, it may lead to changes in metabolic and hormonal function, which affect performance, growth and health. One outcome of low energy availability in female athletes is a disturbance of reproductive function and menstrual regularity. Other problems are likely to occur in male athletes. 

There is a real danger that the focus on achieving a specific body mass and body composition, may become  more important than achieving success in competition. Monitoring of body mass can provide a useful index of energy balance in some situations, but other biomarkers are generally better. Measurement of body fat stores, usually by measurement of skinfold thickness, can be helpful in setting targets and in monitoring progress. Other markers, such as measurement of urinary ketone levels, can identify athletes who are failing to achieve an adequate carbohydrate intake. 

Problems are most likely to occur when the energy expenditure is either very high or very low. Athletes with very high energy demands are likely to be training at least twice per day, leaving limited opportunities for eating the large amounts of foods that are necessary. Athletes with low energy demands and who must restrict energy intake to achieve a low body mass have two main problems: they must cope with constant hunger and they must also be careful in their selection of foods to ensure that they achieve an adequate intake of essential nutrients. 

An athlete’s energy requirements are set primarily by the training load and by body mass, although there is also a large interindividual variability even when these factors are constant. Measurements of oxygen uptake, heart rate, and other variables made after exercise show that the metabolic rate may remain elevated for at least 12 h and possibly up to 24 h if the exercise is prolonged and close to the maximum intensity that can be sustained. After more moderate exercise, the metabolic rate quickly returns to baseline level. 

Therefore, it seems likely that the athlete training at near to the maximum sustainable level and who already has a very high energy demand will find this increased further by the elevation of postexercise metabolic rate: this will increase the difficulties that many of these athletes have in meeting their energy demand. The recreational exerciser, for whom the primary stimulus to exercise is often to control body mass or reduce body fat content, will not exercise hard enough or long enough to experience substantial elevations of metabolic rate after exercise.


Source: Nutritional Supplements
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