Physiology Health Exercise Lesson 15 z Body Composition

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

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

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

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

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

Body Composition Why is it important to assess body composition? 1. To assess the health risk associated with too much or too little fat 2. To monitor weight loss in an obese individual 3. To monitor changes in body composition associated with some diseases like cancer 4. To monitor the effectiveness of exercise training programmes in athletes 6

Body Composition How to measure? 1. Densitometry 2. Skinfold thickness 3. Bioelectrical impedance analysis 4. Body Mass Index (BMI) 5. Waist/hip ratio 6. Mid-upper arm circumference 7

Densitometry z z Fat is less dense than lean tissue Fat density is 0. 9 g cm-3 Fat-free tissue density is 1. 1 g cm-3 If measure density then can predict the relative proportions of lean and fat tissue in the body Density = mass volume z Volume measured by Archimedes Principle! 8

Densitometry z Once density determined, % body fat is calculated as follows: % body fat = 495 density - 450 z Person A & B both have a mass of 60 kg. Person A displaces 56. 9 litres of water and B displaces 58. 3 litres. z Calculate % body fat for both z Who is overweight? 9

Densitometry- answer z Person A has 19. 42% body fat z Person B has 30. 97% body fat z Person B is overweight 10

Densitometry- advantages z Accurate method 11

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

Densitometry- Bod Pod 13

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

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

Skinfold thicknessadvantages z z z Non-invasive Relatively cheap Portable Quick Accurate once the skill has been mastered 16

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

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

Bioelectrical impedance analysis (BIA) 19

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

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

Body Mass Index (BMI) z Most commonly used index of over or underweight BMI = body mass height 2 z Units are kg/m 2 22

Body Mass Index (BMI) Classification BMI (kg/m 2) Underweight <18. 5 Associated health risks Low Normal 18. 5 - 24. 9 average Overweight Moderate Obese class III >25. 0 -29. 9 30. 0 -34. 9 35. 0 -39. 9 >40 Increased Moderately Severely Very severely 23

Body Mass Index (BMI)caution! z Classification can result in an individual being classified as overweight or obese when have a relatively low % body fat, but large muscular bulk z E. g. body builders, weight lifters & other athletes with large muscle bulk y Body-builder with mass 130 kg & height 1. 90 m would have BMI of 36. 01 kg/m 2 & be classed as obese class II 24

Body Mass Index (BMI) 25

Body Mass Index (BMI)questions z Try the following questions: 1. Person A is 150 cm tall & has a body mass of 65 kg. What is her BMI? 2. What classification would she have? 3. How much weight would she have to lose for her BMI to be within the normal range? 4. Person B is 170 cm tall and weighed 69 kg. He recently lost 15 kg on a diet. Explain how his BMI has changed & what could happen if he continues to lose weight. 26

Body Mass Index (BMI)answers 1. Person A has a BMI of 28. 9 kg/m 2 2. She is moderately overweight. 3. She would have to lose 9 kg 65 - (24. 9 x 1. 5) 4. At start B has BMI of 23. 9 kg/m 2 normal After weight loss BMI is 18. 7 kg/m 2 close to underweight which could have a negative impact on his health 27

BMI - advantages z Easy to calculate 28

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

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

Waist/Hip ratio 31

Waist/Hip ratio z 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. z Use the same units for both! z Repeat 3 times and take an average 32

Waist/Hip ratio z For women 0. 8 pear shape & > 0. 8 apple z For men 1. 0 pear shape & > 1. 0 apple z At risk values are > 1. 0 for men & > 0. 8 for women 33

Waist/Hip ratio z 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. 34

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

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

Mid-upper arm circumference z 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 37

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

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

Your mission…. . Work out your body composition using the following methods: 1. Skinfold thickness 2. Body mass index 3. Waist/hip ratio 4. Mid-upper arm circumference z Record 1 & 2 on your personal profile sheet z Make a comment on your observations 40