• Body composition methodology
• Weight loss
• Assessing validity and reliability of test of physiological parameters
• Elite performance
• Ultrasound

Body composition is an important determinant of health and performance. In ‘weight-sensitive sports’, among which are aesthetic sports, weight class sports and gravitational sports (in which body weight influences performance), many athletes use extreme methods to reduce weight rapidly or maintain a low body weight in order to gain a competitive advantage. As a consequence, athletes with very low bodyweight, extreme weight changes due to dehydration or eating disorders, extremely low body fat content, or insufficient bone mineral density are encountered with increasing frequency in many sports.1–5 In weight-sensitive sports, low bodyweight should be seen as only one possible performance factor among others. A deliberately induced underweight condition or short-term weight reduction may lead to severe medical problems, and loss of tissue can cause disastrous performance setbacks due to decreased muscle strength, general weakness, increased susceptibility to illness and reduced ability to cope with pressure: in extreme cases, athletes may develop a clinical eating disorder which is accompanied by severe mental and physical effects that may prove fatal.1 ,6 ,7

The health of the athlete is a precondition for optimum performance. Adipose tissue functions as an endocrine organ and is important in terms of health; it is not just ‘ballast’, as might be urged from a biomechanics perspective. Severe health problems resulting from eating disorders have been reported in many sports, with a higher frequency being found in women (termed ‘the female athlete triad’ when associated with amenorrhoea and osteoporosis).1 Negative effects of acute body weight reduction on health and performance have also been described repeatedly in various sports.8–10 Some International Sport Federations have changed their regulations in an attempt to protect the athlete’s health and it is to be hoped that others will follow these examples. Better protection of the athlete’s health and performance, however, depends on the availability of accurate, precise and valid methods for the assessment of body composition.

The body mass index (BMI) is widely used for defining ‘low weight’, but this is a very rough measure for ‘relative weight’ (an improvement would be to consider individual leg length)4 ,11 ,12 and the BMI cannot be used to characterise athletes’ body composition. Currently, there are no generally accepted lower limits of weight, fat mass or hydration status in male or female athletes that can be used as scientifically based threshold values for raising the alarm or for removal of athletes from competition.5 There are two reasons for this unsatisfactory situation: first, valid methods with sufficient accuracy for body composition assessment in athletes that are applicable in the field are still missing, and second, interpretation of the body composition data of athletes in various sports is a complex task, particularly because individual as well as general sexual dimorphism underpins differences that require consideration. Body composition data must be seen in the context of other health parameters for medical diagnoses. Longitudinal changes in body mass and body composition should also be followed for an accurate assessment of the health risks associated with precompetition manipulation of body mass.

To reduce the risk of health hazards due to dangerous body composition strategies, accurate assessment of body composition is a crucial diagnostic factor, but this is not an easy task. The Ad Hoc Working Group on Body Composition, Health and Performance of the IOC Medical Commission has surveyed the methods currently in use13 and stated in a recent publication on Current status of body composition assessment in sport that many techniques have been proposed for assessing body composition, but “… today there is still no gold standard for body fat assessment with accuracy better than 1%” and “… all of the techniques in common use have some inherent problems, whether in methodology, interpreting the data, or in the assumptions they make. Limitations in both the two-component model (accuracy) and multi-component model (practicality) highlight the desire for an economical laboratory or field approach to body composition assessment that is both accurate and objective... Many coaches and sport scientists anticipate the future development of a minimum sum of fat thickness, which corresponds to a minimum whole body % fat, for the establishment of participation standards for all athletic groups. While the available body composition methods do not permit this at present, some of the emerging medical imaging technologies may achieve the required accuracy to make this a reality in the future.”14

Accurate, reliable and valid body composition measurement techniques that can be employed in the field are urgently needed. Diagnostic ultrasound (US) in combination with accurate image evaluation procedures for multiple thickness measurements of adipose tissue layers seems promising. However, systematic research to determine the best sites for US measurement of subcutaneous fat in terms of simplicity and distinctness of US image evaluation and in combination with validation studies is needed for optimisation and standardisation of this measurement approach. This is particularly true at the extremes of physique and body composition that are found in elite sport: none of the currently available methods can be considered entirely acceptable for these populations. The sites (of a pool of advantageous sites in terms of anatomical clearness) that provide the highest predictive value for total body fat should be selected for standardisation of the US approach.

US has several important advantages: no ionising radiation is applied; fat thickness layers can be quantified across a wide range; embedded fibrous tissues can be quantified; many thickness measurements from one image result in small SEs of the mean; rapid data acquisition and evaluation is possible; participant involvement is minimal; it is applicable in the field and costs are low relative to other medical imaging techniques. Results presented in the November issue of the British Journal of Sports Medicine15 ,16 indicate the potential of this new method for subcutaneous fat assessment to replace currently used measurement techniques like skinfolds or bioimpedance with their well-known inherent shortcomings. It can be assumed that the steadily decreasing price of US imaging systems will contribute to the spread of this emerging measurement technique for fat assessment in sports, with potential health benefits for the athlete.13