In June 2023, the U.S. Army published a new Army Directive 2023-11 entitled "Army Body Fat Assessment for the Army Body Composition Program".
The Directive not only announces changes to the Army Body Composition Program (ABCP) « to ensure that all Army Soldiers maintain a level of physical readiness necessary to perform their duties" but also introduces the gradual implementation of a new one-site circumference-based tape method for estimating percentage body fat.
A new Body Fat Calculator, designed for a circumference-based tape test, was made available on the Army's Ready and Resilient website. This new one-site tape test replaces the previous multi-site tape test prescribed in Appendix B of Army Regulation 600-9 (2019) and is purported to provide a more accurate assessment of body fat.
Source: Army Regulation 600-9 (2019)
However, the Directive does not explicitly reference the study that informed the new body fat calculator. Recent papers authored by researchers from USARIEM continue to adopt the previous models outlined in Army Regulation 600-9 (for instance, Foulis et al., 2023 ; McClung et al., 2022). To our knowledge, the details of the study leading to the new regression model for predicting body fat percentage have not been published in scientific journals. It is conjectured that the new formulas for estimating body fat are derived from the Army Comprehensive Body Composition (ACBC), directed by the U.S. Army Research Institute of Environmental Medicine (USARIEM) and the U.S. Army Center for Initial Military Training (USACIMT), through a cross-divisional team:
The ACBC is an Army-wide study of more than 2,690 Soldiers evaluating the effectiveness of the tape test and providing the scientific data and analysis to advise Army senior leaders to make data-driven decisions about the future of the ABCP" (Phillips, 2023).
An overview of the ACBC study was located on the USACIMT website, attributed to the Fort Lee Army Wellness Center.
At Biotonix, we have applied machine learning techniques to extrapolate the underlying formulas used in the new Body Fat Calculator. By analyzing the 2023 ARMY CALCULATED PERCENT (%) BODY FAT tables for females and males found on the calculator's webpage, we fitted linear regression models to predict % body fat (BF) from body weight (BW) and abdominal circumference (AC, measured around the belly button). After appropriate transformations were applied to the data, we derived regression models to estimate % BF for males and females.
Given that both R² values of the fits are 1 (indicating perfect fits), we deduced that the tables available on the calculator's website were constructed for a range of BW and AC values using the functional forms of the regression models that researchers had previously derived from their data. Standard errors for these new BF estimates, however, were not provided. Considering that Hodgdon & Friedl (1999) reported a standard error of 3%–4% BF for similar models, we infer that the new standard errors should be equal to or less than 3%. Those authors also suggested that trained observers can achieve reproducible results within 1% BF, which should represent an upper limit for the current estimators since they require measurement of only one body circumference with a tape measure.