Extremely low body weight and associated eating and body composition disorders are becoming prevalent in many sports, and can be summarised into three groups:

I. Sports in which weight restricts performance due to mechanical (gravitational) reasons. Among these are ski jumping, high jumping, long-distance running, jockeying, sport climbing, mountain running, up-hill bicycling, etc.

II. Weight class sports in which unhealthy short-term weight reduction behaviour, associated with extreme dehydration, can be observed because the athletes await an advantage when they are classified in a lower weight class. This group includes: wrestling, judo, boxing, kick-boxing, taekwondo, weight lifting, rowing, etc.

III. Aesthetic sports, in particular judged female sports, in which athletes (or their coaches) expect higher scores when their body weight and shape conform to their perceived body-ideals, eg, rhythmic and acrobatic gymnastics, figure skating, diving, synchronous swimming, dancing, etc.

The reasons why weight can be a performance factor are manifold and the effects have to be analysed within the context of all other performance determinants of a given sport. In climbing, for instance, it is the relation of force applicable through the fingers and toes to the body weight that determines performance to a large extend. In sports in which the body mass has to be lifted in the earth’s gravitational field low body weight will result in higher speed at a given energy turnover rate and mechanical efficiency of the human body. The role of weight as a performance factor in ski jumping has been studied in detail recently.1 2 3 4 5 6 7 8 9 In long distance running mechanical work necessary for accelerating body parts, and the body’s centre of mass at every step can be expected to be lower when compared with heavier athletes. However, the analysis of running economy is complex and weight is …