There are various calculations that are useful to the weight trainer and general public alike. In this article I’ll take a look at some of those calculations.
I have created a calculator for some of this stuff if you’d want to skip the various formulae below and just find out your own body stats.
BMI stands for Body Mass Index and it’s used all over the world to assess whether people are underweight, overweight, obese or whatever. It’s a bit of a blunt instrument, particularly for people with a lot of muscle mass and a good health professional should take that into account (although they sometimes don’t).
It’s a simple calculation:
BMI = (weight(kg))/(height(m) x height(m))
Basically, you divide your weight in kg by your height in metres squared. the equivalent in lbs and inches is:
BMI = ((weight(lb))/(height(in) x height(in))) x 703
Once you have your BMI, you can compare it to the following table to see where you stand:
|< 15.0||Very Severely Underweight|
|30.0||34.9||Obese Class I (Moderately Obese)|
|35.0||39.9||Obese Class II (Severely Obese)|
|> 40.0||Obese Class III (Very Severely Obese)|
Once you have your BMI, you can use a formula to get an estimate of your body fat perecntage.
For men, that formula is:
Body Fat = (1.2 x BMI) + (0.23 x age) – 16.2
For women, the formila is:
Body Fat = (1.2 x BMI) + (0.23 x age) – 5.4
Lean Body Mass
Once you have your body fat calculation, you can work out your lean body mass as follows:
Lean Body Mass = weight – ((weight/100) * body fat)
Base Metabolic Rate (BMR)
Your base metabolic rate is the number of calories you burn each day just to exist. That is, the number of calories you’d burn if you spent all day in bed doing nothing. These are the calories your metabolism uses just to keep your body functioning.
There are a few formulae for calculating BMR. Two of the one often used are Mifflin and Katch. Those formulae are as follows:
Mifflin (male) = ((10 * weightKg) / 1) + ((6.25 * heightCm) / 1) – ((5 * age) / 1) + 5
Mifflin (female) = ((10 * weightKg) / 1) + ((6.25 * heightCm) / 1) – ((5 * age) / 1) – 161
Katch (Both Sexes) = 370 + (21.6 * lean body mass (kg))
Total (Daily) Energy Expenditure (TEE or TDEE)
As I mentioned above, BMR is what you’d burn doing nothing but most people have some activity in their day. I’m not talking about planned exercise here but walking to work or the shops. And a person with a construction job will burn more calories than an office worker.
So to get your TEE, you need to multiply your BMR by an ‘Activity Factor’. It’s sometimes hard to establish this activity factor accurately but the following is a reasonable guess:
|< 1.00||Extremely inactive (ill or bed-ridden)|
|1.00||1.19||Very Inactive (no walking anywhere etc.)|
|1.20||1.39||Very Sedentary (eg. office worker, little walking)|
|1.40||1.69||Sedentary (eg. office worker, 30 mins or so light walking or cycling)|
|1.70||1.99||Moderately Active (eg. construction worker)|
|2.00||2.40||Vigourously Active (eg. farm worker)|
|> 2.40||Extremely Active (eg. professional sportsman)|
So, multiply your BMR by the activity factor and you’ve got the number of calories you burn each day.
A Better Way To Calculate TEE
All of the above formulae are prone to error simply because they are fomulae. They take no account of individual metabolisms and they take no account of body composition (i.e. how much muscle mass you have).
The best way to calculate your TEE is to do it manually.
Weigh yourself. Accurately record every calorie you eat for at least 14 days (30 would be better). This means weighing your food and keeping a record of everything.
At the end of the period (14 or 30 days), weigh yourself again.
For every lb of fat you’ve gained in the period, subtract 3,500 calories from the total calories you’ve consumed during the period (or, if you want to work in kg, subtract 7,700 calories for every kg you’ve gained).
If you’ve lost weight during the period add that number of calories instead.
Now divide that number by the number of days in the period (14, 30 or whatever) and you have a TEE value tuned to your particular metabolism and activity level that’s much more accurate than any formula.
This assumes you’ve done no planned exercise during the period. If you have, you’ll need to subtract the calories you burnt exercising from the figure before you divide it by the number of days. TEE values are usually calculated to be what you’d burn without planned exercise.
I hope you’ve found this useful.