Sitting height as a better predictor of body mass than total height and (body mass)/(sitting height)3 as an index of build

Background: The Rohrer Index and the ratio of sitting height (SH) to height fall similarly with growth in early childhood, then level off and rise slightly towards adulthood. In adults the BMI correlates with SH/height. The mean cross-sectional areas of the legs of adults are correlated positively with upper body masses and negatively with leg lengths. Aim: To find an index of body build that is less dependent on relative leg length and age in children and adults than are the BMI and the Rohrer Index. Subjects and methods: Published data are analysed to establish the relative importance of SH and leg length as predictors of body mass and to investigate the age dependence of the ratio (body mass)/SH3. Results: SH is a much better predictor of body mass than height, with leg length being barely relevant. Average values of (body mass)/SH3 vary very little over the age range of 1–25 years, despite small non-random fluctuations. Conclusion: The ratio (body mass)/SH3 is proposed as a useful “sitting-height index of build” that is superior to the Rohrer Index and could prove better than the BMI as a predictor of adiposity. Further studies are needed, notably using individual data and fat-free masses