Background: The growing prevalence of obesity is a known concern along with its associated public health consequences. Body mass index (BMI) is a measure of weight (WT) relative to height (HT) and is the leading metric used to assess weight status. However, waist circumference (WC) may be more predictive of poor health outcomes. A body shape index (ABSI) is a measure of WC that controls for both HT and WT. The primary purpose of this study was to determine the need and justification for a new body shape index (BSI) measure designed specifically for physically active college-aged males. Methods: A convenience sample of N = 80 traditional male college students were used in this study. Body measures of HT (cm), WT (kg), and WC (cm) were objectively measured and BMI (kg/m²) computed. Percent body fat (PBF, %) was used to validate the different indices. A nonlinear power function was developed to create the new allometric-derived BSI. Pearson correlations were used to compare the effectiveness of ABSI and BSI measures. Regression models were used to examine the independence of BSI with HT, WT, and BMI. Cochran-Armitage tests of trend were used to examine the relationships between BSI risk (top 25%) and body measure tertiles. Finally, agreement statistics were computed to present validity evidence for a simpler BSI formula. Results: The new allometric-derived BSI was established as BSI = WC/(WT^0.516×HT^-0.362) with a sample mean of 55.9 (SD = 3.1). ABSI was correlated with WT and BMI but not correlated with PBF. Conversely, BSI was not correlated with WT or BMI but was correlated with PBF. Regression models predicting PBF with BSI and HT, BSI and WT, BSI and BMI, and BSI, HT and WT consistently presented BSI as a significant predictor with all VIF values < 1.26. A significant linear trend in proportions was observed with high-risk BSI and PBF tertiles but not HT, WT, or BMI tertiles. Finally, a simpler approximate BSI = WC/(WT^1/2×HT^-1/3) showed excellent agreement (R² = .998, ICC = .999, p < .0001) with the allometric-derived BSI. Conclusion: This study presents evidence for a new BSI measure that is specifically designed for physically active college-aged males. The BSI for this population is adequately scaled for HT and WT, lacks correlation with BMI, independently predicts PBF, and includes a valid and simpler form for field usage. Further research may be needed to justify population-specific and/or study-level BSI measures.

Body shape index (BSI), body composition, Physical activity, measurement