Body Fat % (Durnin-Womersley 4-Site)

About Body Fat % (Durnin-Womersley 4-Site)

The Durnin-Womersley skinfold equations, published by J. V. G. A. Durnin and J. Womersley in 1974 in the British Journal of Nutrition, are the classic alternative to the Jackson-Pollock generalized equations. Whereas Jackson-Pollock used a single polynomial equation with age as a continuous variable, Durnin and Womersley stratified their sample by age decade and sex and produced a set of simple log-linear equations of the form density = c - m x log10(sum of four skinfolds). The four sites are the biceps, triceps, subscapular, and suprailiac, which together capture the major subcutaneous depots of the upper body.

How the formula works

The Durnin-Womersley equations compute body density from the sum of the four skinfolds (in millimeters) and age- and sex-specific intercept (c) and slope (m) coefficients. For men the coefficients are: ages 17-19 (c=1.1620, m=0.0630), 20-29 (1.1631, 0.0632), 30-39 (1.1422, 0.0544), 40-49 (1.1620, 0.0700), and 50+ (1.1715, 0.0779). For women: ages 16-19 (1.1549, 0.0678), 20-29 (1.1599, 0.0717), 30-39 (1.1423, 0.0632), 40-49 (1.1333, 0.0612), and 50+ (1.1339, 0.0645). The resulting body density is converted to percent body fat using the Siri equation (percent fat = 495/density - 450). The log-linear form reflects the fact that body density decreases roughly linearly with the log of subcutaneous skinfold thickness, a relationship that holds across a wide range of adiposity.

Sites and technique

The biceps site is a vertical fold on the anterior mid-upper arm. The triceps is a vertical fold on the posterior mid-upper arm. The subscapular is a diagonal fold 1 to 2 cm below the inferior angle of the scapula. The suprailiac is a diagonal fold just above the iliac crest in the midaxillary line. All four sites are on the upper body, which makes the Durnin-Womersley method convenient but also means it may under-represent lower-body fat, an important consideration for women and individuals with gynoid distribution.

Evidence and validation

Durnin and Womersley derived their equations from 482 men and women aged 16 to 72 and cross-validated against underwater weighing, reporting standard errors of estimate of about 3.4 percent body fat in men and 3.6 percent in women. The equations have been validated extensively in European, South Asian, and East Asian populations, with generally good performance in lean to moderately overweight adults but systematic underestimation in the obese, because the log-linear form extrapolates poorly at very high skinfold sums. The Durnin-Womersley equations are recommended by the World Health Organization for field surveys and remain the standard in much of the European nutrition literature.

Interpretation

Percent body fat values can be interpreted using the same ACE categories as other skinfold methods: athletic 6-13 percent (men) and 14-20 percent (women), fitness 14-17 percent and 21-24 percent, acceptable 18-24 percent and 25-31 percent, and obesity above those ranges.

Limitations

The Durnin-Womersley equations are stratified by decade, which produces small discontinuities at age boundaries, and the upper age limit (72 years) and lower limit (16 years) constrain their applicability. Because all four sites are on the upper body, the method is less representative than the Jackson-Pollock 7-site equation for individuals with significant lower-body adiposity. As with all skinfold methods, technician skill is the dominant source of error, and the Siri two-component conversion assumes constant fat-free mass density, which introduces error in athletes, the elderly, and children.