Objective: Children and adolescents are often involved in sports in which weight loss is perceived as an advantage. Adolescents try to lose weight or body fat in the interest of improved appearance or athletic performance. Unhealthy weight-control practices can impair athletic performance and increase injury risk. They also may result in medical complications including delayed physical maturation, oligomenorrhea and amenorrhea in such as the female athletes, development of eating disorders, potential permanent growth impairment, etc. Body mass index (BMI, kg/m²) is the most widely used screening tool for underweight, especially in general practice. In athletes BMI as indicator of thinness can be questioned. The aim of the study was to determine sensitivity and specificity of thinness among healthy young athletes based on body mass index (BMI, kg/m²) (using the IOTF criteria ), and the % body fat (%BF) determined by the bioimpedance method and using percentile lines from UK study .
Subjects and methods: We used data from the Sports Medicine State Agency database on health check-ups conducted between 2008 and 2009. Cross-sectional study using cluster sampling (sports organisations) was implemented, analysing data from 7 667 young athletes (5222 male and 2 445 female) at age from 7 to 17 years old. Athletes were categorised as belonging to lean (n=2 390) or non-lean (n=5 277) sports . Body composition (%BF) was measured by a multi frequency 8-polar bioelectrical impedance leg-to-hand analyser (X-Scan pluss II, Korea).
Results: The prevalence of underweight according to IOTF BMI cut-off values was 3,2% (n=216, CI 95% 0,88-5,6), the corresponding values of underfat using body fat cut-offs was 59,42% (n=4556, CI 95% 58,32-60,52). The performance of BMI cut-off values for identification of thinness individuals with %BF as reference is displayed in Table 1 [Tab. 1].
Conclusion: The sensitivities of the BMI-derived cut-offs were mostly below 20%, while the specificities were high. Our results suggest that the low sensitivity IOTF BMI cut-offs leads to a considerable underestimation of the true prevalence of thinness in youth athletes.
7th EFSMA – European Congress of Sports Medicine, 3rd Central European Congress of Physical Medicine and Rehabilitation. Salzburg, 26-29 October 2011