Muscle mass index estimated by anthropometry vs bioelectrical impedance: Study in athletes competing by weight categories

The aim of the study was to compare the muscle mass obtained by anthropometry and bioelectrical impedance, in athletes competing by weight categories. 109 (42 women y 67 men), age 21.4 ± 3.5 years, boxing (32), weightlifting (16), judo (28), karate (12), fighting (14) and taekwondo (7) practitioners were selected. The protocol included nineteen anthropometrics variables and a bioelectrical impedance analysis (akern®), estimating the muscle mass by anthropometry by the Lee's equation (2000) and by bioimpedance by Janssen's equation (2000), calculating the muscle mass index (IMM, kg/m²). In ten athletes it was examined whether in a second exploration the changes over time were similar by both techniques. The intraclass correlation coefficient (ICC) and the Bland-Altman analysis were applied to assess the concordance. Results: The IMM estimated by Lee vs Janssen, was in the female sample, 9.01 ± 1.01 kg/m² vs 8.68 ± 1.1 kg/m²; and in the male sample, 11.17 ± 1.34 kg/m² vs 11.04 ± 1.13 kg/m² .The ICC was 0.945 [95%IC; 0.915-0.964]. The difference in the IMM between both techniques was 0.21; with a confidence range of 95% between +1.60 a -1.18. In the longitudinal study, five of the athletes controlled (50%), gave differences in the assessment of their IMM's changes. We concluded that even though in a statistical sense there is a high concordance between both equations being valid for epidemiological studies, the differences found cannot be assumed as interchangeable for the individual assessment of each athlete nor in comparative studies.