# Physiology, Health & Exercise

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

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

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

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

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

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

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

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

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

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

Accurate method

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

Densitometry- Bod Pod

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

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

Non-invasive Relatively cheap Portable Quick Accurate once the skill has been mastered

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

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

Bioelectrical impedance analysis (BIA)

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!

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

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

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

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

Body Mass Index (BMI)

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.

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

BMI - advantages Easy to calculate

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

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

Waist/Hip ratio

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

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

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.

Better estimate than BMI for some Easy to calculate Requires little equipment

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

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

Easy to calculate Requires little equipment Easy to perform Quick to carry out

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

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