Exercise - Day 17

What is BMI?

It was pointed out to me yesterday that i am mis-representing BMI as a % when in fact it is a number, so never one to take an individuals word for it i did a bit of research and i think i have got to the bottom of it now.

The Body Mass Index (BMI) and its equation was the brainchild of a Belgian social physicist Adolphe Quetelet who in 1835 published a book titled in English as 'Treatise on Man' which explained his take on a type of social physics regarding what he thought to be the average man, by using various statistical data and equations Adolphe was able to explain that variables linked to social factors contributed to crime, marriage and suicide rates, his research led him to the conclusion that a population produces enough variables for both artificial selection (selective breeding) and natural selection to occur side by side.

BMI a simple means of classifying a persons weight relative to an ideal weight for their height was originally intended to be used as a measure of a populations overall risk of health problems due to weight gain or loss.  Now used in individual cases BMI gives us a fair indication of the thickness or thinness of a person compared to the national average of sedentary persons who are considered to have an average body composition.  Once calculated BMI can be compared to a sliding scale of ratios which can give a person a rough idea of which health issues they may experience based on historical statistical data collected from others of similar height and weight.

The equation for calculating BMI is as follows:

Metric
(Weight kg/height m) / height m = BMI
Imperial
(Weight lb/height inches) / height inches x 703 = BMI

My metric equation looks like this:
(161.1/1.80) = 89.5
89.5/1.80 = a BMI of 49.72

My imperial equation looks like this:
(355.17/70.87) = 5.0116
5.0116/70.87 = 0.0707
0.0707x703 = a BMI of 49.70

Now as a western male i can compare my result to the data held by my local health authority of choice which in my case is the UK National Health Service (NHS), their ratios are as follows:

BMI score below 18.5 = underweight
BMI score between 18.5-24.9 = healthy weight
BMI score between 25-29.9 = overweight
BMI score between 30 and above = Obese

With a BMI of 49.7 i am classified as obese compared to normal height to weight ratio of what is considered the norm for people of a healthy weight.  Due to my classification falling above 25 i am statistically more at risk from developing heart related diseases, type II diabetes or experiencing a stroke.  A BMI below 18.5 could show signs of eating disorders such as anorexia or bulimia.  In all ranges it is advised people eat a well balanced diet and partake in some form of exercise to maintain a healthy BMI between 18.5 and 24.9.

The one problem with BMI is the fact that the number does not take into account the physical composition of fat v muscle nor does it give us a clear indication of the norms within a certain age range or bone density therefore the results can be misleading in children, the elderly or athletes, to combat this there are many ways to calculate body fat some more accurate than others, from underwater weighing to the more modern techniques such as duel energy X-ray absorptiometry but not everyone has access to a science lab or can afford such procedures to be carried out, the US Navy has a system using logarithms which can determine a persons overall fat content determining the criteria for entry into the armed forces which uses measurements such as neck, waist, hip size but again to manually use the equation can be a bit taxing for us mere mortals, so for us we can stick to the following equation formulated by nutritionist Paul Deurenberg for calculating an estimated Body Fat Percentage (BF%):

Adult BF% = (1.2 x BMI) + (0.23 x Age) - (10.8 x sex) - 5.4
sex = 1 for males and 0 for females.

My equation looks like this:

(1.2 x 49.7) + (0.23 x 39) - (10.8 x 1) - 5.4

So my BF% is calculated as follows:

59.64 + 8.97 - 10.8 - 5.4 = 52.41

My calculated BF% is 52.41, now lets compare with data again collected from the my local health authority of choice the NHS:

Essential fat

• Women 10-13%
• Men 2-5%

Athletes

• Women 14-20%
• Men 6-13%

Fitness

• Women 21-24%
• Men 14-17%

Average 

• Women 25-31%
• Men 18-24%

Obese

• Women 32%+
• Men 25%+

Essential fat levels are the bare minimum we need to be at to not negativly impact our health but it is important to mention that athletes such as bodybuilders may compete at even lower ranges as recommended to them by certified personal trainers.  Female ranges are higher due to the effects of childbearing and other hormonal functions. 

Now i know where i need to be with my BMI and BF% and the person who corrected me yesterday on my reporting of BMI was indeed correct BMI is a number and BF is a percentage. 

So on that note exercise yesterday consisted of 14,778 steps from my daily routine, a lunch time walk and after work stroll with Ryan on his green machine (bicycle)

Once month one has been completed i am contemplating adding to my walks with some beginners aerobics combined with light weights, stay tuned...