For example, the density of fat-free mass in 8 year old boys is 1.088 g/cc and for girls it is 1.090 g/cc 25, as opposed to the value for adults of 1.100 g/cc. In children and adolescents, the chemical composition of the body changes, particularly with respect to the decreasing water and increasing mineral content of fat-free mass. Lohman 24 and Wells 25 have published age and sex-specific constants for children to be used in equations similar to that of Siri, that take into account the chemical immaturity of the growing child. The Siri and Brozek formulas ( Table 19.3) are the most widely used conversion formulas in adults. However, these constants vary with growth, maturation, illness, degree of obesity and aging.
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The method is based on several assumptions, including the assumption that the densities of the major tissue compartments (density of fat = 0.900 g/cc and fat free mass = 1.100 g/cc) are essentially constant across individuals. Body density is then used to estimate fat-free mass, fat mass and percent body fat using conversion formulas. Durnin and Womersley derived values for calculation of fat mass for all age groups in both men and women.ĭensitometric methods are based on the principle that body density can be determined as body mass divided by volume. Depending on the equation used and the population studied, this may range from 3 to 9% body fat mass. In general, the error of this method is approximately 5%. 4.įat-free mass (kg) = body weight (kg) − body fat (kg).īoth the skill of the operator and the character of the subcutaneous fat in an individual can influence the precision of skin-fold measurements. Total body fat is derived as follows: total body fat (kg) = /100. The Siri equation assumes that the density of fat is 0.900 g cm −3 and that the density of the fat-free mass is 1.100 g cm −3: % fat = × 100. Percentage body fat or relative fat mass can then be calculated. Using regression equations such as Durnin and Womersley's, skin-folds, sex, and age are used to derive body fat and fat-free mass. Multiple skin-fold sites can be assessed and usually include both limb and trunk sites.īody density can be estimated from skin-fold measurements. The fold should remain held whilst the measurement is taken.
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The calipers are applied at right angles to the skin at the midarm point and 1 cm in from the surface. Using the thumb and forefinger, the skin-fold is grasped just above the midarm point. The arm is then extended and allowed to hang loosely by the side. With the elbow bent to 90% the midpoint is located half-way between the acromium process of the shoulder and the olecranon process of the ulna. The measurement of the triceps skin-fold is taken at the midpoint of the upper arm. However, the triceps skin-fold is most frequently selected for a single-site assessment of body fat. There is no universal agreement as to which skin-fold best represents total body fat.
Skin-fold thickness measurements may be taken at single or multiple sites.
None the less, this method provides useful information and is in routine use. In addition, there are marked variations in the distribution of subcutaneous fat depending on age, sex, and race. This assumption is not strictly true, as the thickness of subcutaneous fat does not necessarily reflect a constant proportion of total body fat.
Strauss, in Encyclopedia of Food Sciences and Nutrition (Second Edition), 2003 Skin-fold ThicknessesĮstimation of body fat content from skin-fold thicknesses assumes that measurements of subcutaneous fat represent total body fat.
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