Physiology, Health & Exercise

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 = 495 - 450 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. Body Mass Index (BMI)

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