MANUAL MEASURES OF BODY MASS AND FAT MASS
Body Mass Index (BMI). BMI (sometimes also called ‘Quetelet’s index’) was developed to account for the influence of height on body mass. The measure is weight (in kg) divided by height (in m) squared, i.e. BMI = wt(kg)/ht(m)2. Recommended ideal range for BMI is 20-25 kg/m2. Overweight is regarded as over these upper levels and the different levels of obesity are defined.
BMI has as its main advantage the ability to be used in large scale population studies. It requires only two measures; height and weight, which can both be measured accurately by a person with minimal training. It suffers similar deficiencies to weight in that it is less valid in those with a mesomorphic build, and particularly athletic men. The validity of BMI, although higher than weight, is lower than is necessary for a good measure of body fatness. Validity has also been found to be higher in women than men and to be significantly influenced by body build.
Comparisons with other anthropometric measures, at least in large populations, show the usefulness of BMI measures. Its reliability is relatively high, but as with weight, this can be influenced by fluid content. Sensitivity could be expected to be similar to that for weight as height is not expected to change significantly, except with age. The BMI therefore is useful for large scale population studies and, in combination with other measures, is useful for individuals. Some researchers have called for the total abandonment of BMI. However, according to Lohman. ‘. . . BMI needs to be included with skinfolds or bioelectric impedence and other laboratory body composition measures of muscle, bone, and fat’.
The limitations of BMI, as with weight, need to be understood in working with individuals, i.e. there is a need to apply other assessments (including a practised ‘calibrated eyeball technique’) to raw BMI data.
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