1. Physiology, Health & Exercise
Lesson 15
Body Composition & it’s Measurement

2. Body Composition & Measurement
Methods include:
Densitometry
Skinfold thickness
Bioelectrical impedance analysis
Body Mass Index (BMI)
Waist/hip ratio
Mid-upper arm circumference
Limitations of each method

3. Body Composition
Measuring someone’s mass does not tell us the whole story
i.e. doesn’t tell us much about their size or composition of their body
2 people can have the same mass but one can have more body fat & the other have less fat but more muscle
Level of fat to muscle better indicator of how healthy someone is

4. Body Composition
Need to determine ratio of fat to lean tissue (muscle, bone etc)  body composition
Remember do need some fat
cell membranes
Formation of some hormones
Insulation
Just not too much fat!!
It is possible to lose fat from body & increase or maintain lean tissue  not much change in mass

5. Body Composition
% of body fat associated with the least health risk is
18-25% for females
13-18% for males

6. Body Composition Why is it important to assess body composition?
To assess the health risk associated with too much or too little fat
To monitor weight loss in an obese individual
To monitor changes in body composition associated with some diseases like cancer
To monitor the effectiveness of exercise training programmes in athletes

7. Body Composition How to measure? Densitometry Skinfold thickness
Bioelectrical impedance analysis
Body Mass Index (BMI)
Waist/hip ratio
Mid-upper arm circumference

8. Densitometry Fat is less dense than lean tissue
Fat density is 0.9g cm-3
Fat-free tissue density is 1.1g cm-3
If measure density then can predict the relative proportions of lean and fat tissue in the body
Volume measured by Archimedes Principle!
Density = mass
volume

9. Densitometry
Once density determined, % body fat is calculated as follows:
Person A & B both have a mass of 60kg. Person A displaces 56.9 litres of water and B displaces 58.3litres.
Calculate % body fat for both
Who is overweight?
% body fat =
density

10. Densitometry- answer Person A has 19.42% body fat
Person B has 30.97% body fat
Person B is overweight

11. Densitometry- advantages
Accurate method

12. Densitometry- limitations
Involves the person being totally submerged under water
May be difficult & produce some anxiety
New method developed using a “Bod Pod” which uses air displacement.
Person sits in a small chamber and body volume calculated by measuring initial volume of empty chamber minus volume with the person inside
Specialised equipment needed

13. Densitometry- Bod Pod

14. Skinfold thickness Most widely used method
Involves measuring the layer of fat under the skin (subcutaneous layer) at several specific sites
Uses a skinfold caliper

15. Skinfold thickness 4 sites are commonly used:
Over the biceps at the front of the arm
Over the triceps at the back of the arm
Under the shoulder blade at the back (subscapular)
Above the hip bone at the side of the body (supra-iliac)
Values added and compared with values in table to predict body density & then body fat

16. Skinfold thickness- advantages
Non-invasive
Relatively cheap
Portable
Quick
Accurate once the skill has been mastered

17. Skinfold thickness- limitations
Errors associated with measurer skill
Does not take into account unusual fat distribution
Difficult in the fat and very obese

18. Bioelectrical impedance analysis (BIA)
Relies on fact that fat is an insulator of electricity whereas fat-free tissue (approx 73% salty water) is a good conductor
Insulators have a higher resistance or impedance to the flow of a small electric current
Greater resistance  greater % body fat
Electrodes placed on the back of the right hand and right foot while subject is lying down

19. Bioelectrical impedance analysis (BIA)

20. BIA- advantages Requires little or no technical skill by the operator
Portable
Quick- takes less than a minute to perform
Only requires removal of a sock!

21. BIA- limitations
Any disturbance in hydration level (e.g. dehydration or oedema) will affect the accuracy of the results
Changes in skin temperature can also affect conduction of the electrical current
Tends to overestimate body fat in very lean, muscular people and underestimate in obese people- so not as accurate

22. Body Mass Index (BMI) Most commonly used index of over or underweight
Units are kg/m2
BMI = body mass
height2

23. Associated health risks
Body Mass Index (BMI)
Classification
BMI (kg/m2)
Associated health risks
Underweight
<18.5
Low
Normal
average
Overweight
Moderate
Obese class I
Obese class II
Obese class III
>25.0
>40
Increased
Moderately
Severely
Very severely

24. Body Mass Index (BMI)- caution!
Classification can result in an individual being classified as overweight or obese when have a relatively low % body fat, but large muscular bulk
E.g. body builders, weight lifters & other athletes with large muscle bulk
Body-builder with mass 130kg & height 1.90m would have BMI of 36.01kg/m2 & be classed as obese class II

25. Body Mass Index (BMI)

26. Body Mass Index (BMI)- questions
Try the following questions:
Person A is 150cm tall & has a body mass of 65kg. What is her BMI?
What classification would she have?
How much weight would she have to lose for her BMI to be within the normal range?
Person B is 170cm tall and weighed 69kg. He recently lost 15kg on a diet. Explain how his BMI has changed & what could happen if he continues to lose weight.

27. Body Mass Index (BMI)- answers
Person A has a BMI of 28.9kg/m2
She is moderately overweight.
She would have to lose 9kg
65 - (24.9 x 1.5 x 1.5)
At start B has BMI of 23.9kg/m2  normal
After weight loss BMI is 18.7kg/m2  close to underweight which could have a negative impact on his health

28. BMI - advantages
Easy to calculate

29. BMI- limitations
Can lead to wrong classification as does not differentiate between high % fat and high % muscle
Important to differentiate between large muscle bulk and excess fat

30. Waist/Hip ratio
The distribution of fat in the body rather than total quantity is more important
People classed as apples (android) or pears (gynoid)
Apples  extra abdominal fat (“pot-belly”)- have a higher risk of CHD, diabetes etc
Pears  extra fat around the hips & thighs

31. Waist/Hip ratio

32. Waist/Hip ratio
Use a measuring tape to check the waist and hip measurements. - Measure your hip circumference at it's widest part. - Measure your Waist Circumference at the belly button or just above it.
Use the same units for both!
Repeat 3 times and take an average

33. Waist/Hip ratio For women 0.8  pear shape & > 0.8  apple
For men 1.0  pear shape & > 1.0  apple
At risk values are > 1.0 for men & > 0.8 for women

34. Waist/Hip ratio
It is possible to have a high BMI and a normal waist measurement if you are a fit, lean, muscular man. This is why your waist to hip ratio is a better guide to your risk of heart disease.

35. Waist/Hip ratio - advantages
Better estimate than BMI for some
Easy to calculate
Requires little equipment

36. Waist/Hip ratio - limitations
Takes no account of body composition

37. Mid-upper arm circumference
Is the circumference of the left upper arm, measured at the mid-point between the tip of the shoulder and the tip of the elbow

38. Mid-upper arm circumference - advantages
Easy to calculate
Requires little equipment
Easy to perform
Quick to carry out

39. Mid-upper arm circumference - limitations
Better for estimating under-nutrition
Lack of data upon which to decide useful cut-off points
changing patterns of skeletal muscle and subcutaneous fat as people age

40. Your mission…..
Work out your body composition using the following methods:
Skinfold thickness
Body mass index
Waist/hip ratio
Mid-upper arm circumference
Record 1 & 2 on your personal profile sheet
Make a comment on your observations