When it comes to working out your body weight, many of us use the BMI (Body Mass Index) rating as a guide; this uses the square of our height to determine our ideal body weight. The BMI is widely known to be flawed for various reasons: frame size is not taken into account, body composition is ignored (how much stored fat as opposed to lean muscle) and the boundaries between descriptive categories (e.g. underweight, overweight, obese, etc.) are arbitrary decisions.
Body composition is really important if you’re working out, because you could be turning all of that stored fat into lean, healthy muscle, yet your bathroom scales – and your BMI – will remain stubbornly static.
Fortunately, there are several ways in which your body fat percentage can be either estimated or measured. For example there is bioelectrical impedance analysis, near infra-red interactance and, of course, the trusty tape measure and mirror.
Two of the most popular methods for determining body-fat content are hydrostatic weighing and the use of body-fat callipers.
One of the most accurate ways to determine how much of your mass is fat is to undergo hydrostatic weighing. This works on Archimedes’ Principle of displacement and gives a reading which should be accurate to within 4 per cent. First, you will be dry-weighed, and then you will be weighed underwater using specially designed apparatus. The figures will be entered into an equation which takes into account factors such as the amount of air stored in the body. Since the density of adipose tissue (stored fat) and lean muscle are fixed and known, the percentage of each can be derived.
If tracking down a handy hydrostatic tank is a bit inconvenient, a set of body-fat callipers are an adequate alternative. Your measurements can either be converted into a rough estimate of body-fat percentage, or simply recorded and tracked.
The key to effective use of callipers is consistency. Aim to test the same body areas on the same side and at the same time of the day. Repeat at least three times and take an average. The areas of the body that should be measured are the triceps, below the shoulder blade (sub scapular), supraspinale (side of the abdomen), front of the abdomen, thigh and calf.
To convert the measurements to body-fat percentage, men should multiply the sum by 0.1051 and add 2.585. If you are a woman, multiply the sum by 0.1545 and add 3.580.
How Much Fat is Healthy?
Fat is given a lot of bad press, but we need it for temperature regulation, hormone synthesis, organ protection and many other life-preserving functions. Your ideal body-fat composition depends upon your sex and age, with women needing more fat than men. Men should aim for the 9-19 per cent range, with women striving for 14-21 per cent (even up to 25 per cent for the over fifties).
Disclaimer: This blog post is for information only and does not constitute expert advice. For expert dietary advice, consult with your GP, dietician or trusted healthcare expert.
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