This study used a dual-energy X-ray absorptiometry (DXA) method to investigate how body weight relates to fat-free mass index (FFMI) and fat mass index (FMI) in male college judo players. The whole-body fat-free mass and fat mass of 59 male college judo players were measured to the nearest 0.1 g using a DXA method. The fat-free mass and fat mass thus obtained were each divided by the square of the height (m) to give the FFMI and FMI, respectively. The percentage of body mass index (BMI) accounted for by FFMI and by FMI (%) was then calculated. The relationship between body weight and the percentage of BMI accounted for by FFMI and by FMI (%) can be interpreted as two straight lines with a break point. The break point can be determined by a regression analysis of these two straight lines using the plots of the percentage of BMI accounted for by FFMI and by FMI (%) by the least squares method. Using this method, the break point of two straight lines was obtained with the minimum square sum of the residual. The results showed the break point of the plots of percentage of BMI accounted for by FFMI and by FMI against body weight was 87.6 kg for both FFMI and FMI, and that as body weight increased, the proportion of FFMI in BMI decreased and the proportion of FMI in BMI increased. This break point indicates that the limit up to which it is possible to increase weight without worsening the body composition in male college judo players is around 90 kg, and any weight gain above this will depend on an increase in fat more than an increase in muscle.
