Body Mass Index (BMI)

Purpose

Body composition refers mainly to how muscle and fat are distributed in the body; body-size measures such as height, lengths and girths are also grouped under this component. The Body Mass Index (BMI) is the screening measure used here — it relates a person's weight to their height and gives a single number that rises as the proportion of body fat rises.

Infrastructure / Equipment Required

• A flat, clean surface.
• A weighing machine.
• A stadiometer, or a measuring tape pasted on a wall.

Procedure

Measuring height accurately — Remove the participant's shoes, bulky clothing and hair ornaments, and undo any hair that gets in the way of the measurement. Take the measurement on an uncarpeted floor, against a flat wall with no moulding. The participant stands with feet flat and together, back against the wall, legs straight, arms at the sides and shoulders level, looking straight ahead so the line of sight is parallel with the floor. Ideally the head, shoulders, buttocks and heels all touch the wall (depending on body shape, not every point will touch). Lower a flat headpiece, held at a right angle to the wall, until it firmly touches the crown of the head, keeping your eyes level with the headpiece. Lightly mark where the bottom of the headpiece meets the wall, then measure from the floor to that mark with a metal tape. Record the height to the nearest 0.1 cm.

Measuring weight accurately — Use a digital scale (avoid spring-loaded bathroom scales), placed on firm flooring such as tile or wood rather than carpet. The participant removes shoes and heavy clothing such as sweaters and stands with both feet in the centre of the scale. Record the weight to the nearest decimal fraction, for example 25.1 kilograms.

Scoring

BMI is calculated from body weight (W) and height (H):

A higher BMI score usually indicates a higher level of body fat. Height is recorded to the nearest 0.1 cm and weight to the nearest decimal fraction. …