Weight is measured by digital scales or beam balance to the nearest 100 g. For those unable to stand, electronic chair scales (Weighcare C, Marsden Ltd, London) are available. For field work, portable scales are used. Equipment is calibrated regularly by standard weights (4 x 10 kg and 8 x 10 kg), and the results of test weighing recorded in a book. Subjects are weighed in light clothing, fasting and with an empty bladder, preferably at the same time of day.
Height is measured by stadiometer to the nearest millimetre, which is calibrated by meter rule before use. When possible, a wall mounted stadiometer is preferred. For field work, a portable stadiometer (Leicester Height Measure, Child Growth Foundation, London, UK; Holtain, Crymych, UK) is available. Subjects stand in bare feet which are kept together and pointing forward. The head is level with horizontal Frankfurt plane (line from lower border of the eye orbit to the auditory meatus). Subjects are encouraged to stretch upwards by applying gentle pressure at the mastoid processes and height is recorded with subjects taking in a deep breath for maximum measurement.
When height measurement is not available in bed-and chair-bound patients. Height can be predicted from arm span or lower leg length (21). Arm span is measured between finger tips with subjects standing against the wall, and both arms fully stretch horizontally. Demi-arm span is measured as the horizontal distance from the web space between middle and fourth fingers to the midpoint of the sternal notch to the nearest millimetre, in the sitting position. Lower leg length is measured with subjects sitting in a chair adjusted to about their knee height, and the lower legs and bare feet flexed at 90°. The lower legs, 25-30 cm apart, are adjusted to vertical position both side and front views. A ruler standing on its edge is placed on top of the patellae. Lower leg length is taken to the nearest millimetre from the midpoint of the ruler to the floor with a wooden metre rule.
Waist circumference is measured midway between the lower rib margin and iliac crest, with a horizontal tape at the end of gentle expiration (Figure 4.4), with feet kept 20-30 cm apart. Subjects should be asked not to hold in their stomach, and a constant tension spring-loaded tape device reduces errors from over-enthusiastic tightening during measurement. Waist circumference measurement reflects body fat and does not include most of the bone
Figure 4.8 Subcutaneous and intra-abdominal fat images obtained from magnetic resonance imaging. (a, above) Male; (b, opposite) female. Light areas indicate fat structure (only the spine) or large muscle masses, whose variations between subjects might otherwise introduce errors.
Maximum hip circumference is measured with a horizontal steel tape at the widest part of the trochanters at horizontal position (Figure 4.4) with feet kept 20-30 cm apart. It is related more closely to subcutaneous fat than to intra-abdominal fat mass. Hip circumference has limited value on its own in body composition estimation. The circumference of the hip is influenced by gluteal muscle mass and pelvic size, which vary between subjects, as well as by fat.
Thigh circumference is measured at the level of gluteal fold with the leg being measured relaxed by placing it forward and slightly bent, with body weight transferred to the other leg. It estimates fat on the thigh but will also be altered by muscle mass.
Abdominal fat deposition is further classified into medial (fat is accumulated at the middle of the abdomen) and lateral (fat is accumulated at the sides of the abdomen). Waist diameters are measured using a pelviometer or a more expensive device that measures the supine sagittal abdominal diameter (37). The pelviometer is a cheaper instrument
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that looks like a pair of large calipers and measures the waist diameter at the level between the lower rib margin and iliac crest. Waist sagittal diameter is taken as the distance from the back to the front of the abdomen measured with the subject standing. Waist transverse diameter is taken as the distance from the sides of the abdomen.
Skinfold thicknesses are measured on the left side of the body with calipers (Holtain Ltd, Crymych, UK) in triplicate, to the nearest 0.2 mm. All the sites intended for measurements should be marked clearly on the skin after making measurements from bony landmarks (Figure 4.3). When the subjects relax their mucles, the subcutaneous fat layer (commonly referred to as skinfold thickness) covering the muscles is relatively loose and can usually be pinched easily by two fingers (thumb and index finger) which hold the skinfold firmly throughout the measurement (11). The pinch is made at about 1 to 2 cm above the ink mark so that the jaw of the calipers can be applied at the mark. The thickness of the skinfold is read about 2 seconds after closing the jaw of the calipers.
Biceps and triceps skinfold thicknesses are made at the midpoint of the upper arm, between the ac-romion process and the tip of the bent elbow. Sub-scapular skinfold thickness is picked up at the natural fold about 2-3 cm below the shoulder blade in an oblique angle. Suprailiac skinfold is pinched at about 2-3 cm above the iliac crest, in either a vertical or oblique angle on the lateral side and mid-axillary line. The upper limit of skinfold calipers is 50 mm, which is exceeded for the subscapular site when BMI is greater than 40kg/m2. Thus for very overweight people, other methods are required.
Figure 4.10 ''Waist Watcher" tape measures with three colour bands (green, orange and red) based on cut-off waist circumference action levels. (BGA, The Spire, Egypt Road, Nottingham
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