3. Energy costs of growth or changing body mass

The requirement for growth is an important factor in the energy needs of young athletes who have not reached full maturity. In these cases, energy intake must exceed expenditure if growth is to take place. Some athletes, mostly in events where a high power output is an important part of successful performance, will also benefit from an increased body mass, and an increase in muscle mass rather than in fat mass is usually desired. In some events, such as the heaviest weight categories in weightlifting and in the combat sports, and in the throwing events in track and field, a high absolute mass may be important, and a high body fat content is often seen in the most successful competitors. If the body mass is to increase, there must be an excess of energy intake over expenditure. The reverse situation, a need to reduce body mass and especially to reduce the body fat content, is also frequently encountered. There are particular problems in reducing the energy take to a level that will result in a loss of body mass without compromising the ability to sustain the training load. In seasonal sports such as soccer or rugby, a substantial gain in body fat is not unusual in the off season, and the preseason training for these athletes often involves a combination of sudden increases in the training load in combination with a restriction of energy intake. Dietary strategies which assist athletes to manipulate their body mass and body composition are discussed in more detail in Chapters 11 and 13