Arm x-ray assessment of percent body fat in men and women

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Abstract
KATCH, FRANK I. and ALBERT R. BEHNKE. Arm x-ray assessment of percent body fat in men and women. Med. Sci. Sports Exerc., Vol. 16, No. 3, pp. 316–321, 1984. The present experiment determined the validity of arm radiography for quantifying total body fat in young and older men and women. One hundred subjects were measured for 1) body density by underwater weighing with correction for residual air volume to estimate percent body fat and 2) horizontal right upper arm x-ray at KV 76, exposure time 1/30th s, 300 MA, and focal length 72 inches. Total radiation was 10 millirems (mR). The width of fat on the x-ray was measured at three cross-sectional sites (FAT,x-ray). Errors of measurement and measurement for reliability were assessed from duplicate x-rays and repeated measures on the same x-rays (r=0.92–0.99). The equation to convert FAT,x-ray to individual estimates of percent fat is %Fat = FAT,x-ray/3F X k constant, where 3F = 3√wt,kg/ht,dm, and the k constant is a previously determined mean value. The correlation between Fat,x-ray and percent fat (density) was r=0.89 (N=100, Se=±2.54); for 25 young men (ages 18–30), r=0.90 (Se=±1.84); for 25 older men (ages 30–40), r=0.89 (Se=±2.20); for young (N=25) and older (N=25) women, r=0.85 (Se=±2.08) and 0.87 (Se=±2.61), respectively. These results demonstrate that the new, arm radiogrammetric method is a reliable and valid technique for assessment of body composition in men and women ages 18–40 yr. It permits quantification of relative body fat and thickness of muscle and bone for cross-sectional and longitudinal analyses, as well as for clinical evaluation of nutritional status.