ANTHROPOMETRY AND BODY COMPOSITION

Body composition – relative proportion of different components that make up the human body. There are many models through which to look at body composition.

Tissue model - The body is composed of four main tissue types, Nervous, Epithelial, Muscle and Connective tissues.

Nervous tissues– brain, spinal cord, nerves

Epithelial tissues- skin, linings of GI and other hollow organs

Muscle tissues – cardiac, skeletal, smooth

Connective tissues – fat, bone, tendon, cartilage

Several tissue types work together to comprise each organ.

Structural Model - The main structural components of the body are bone, fat and muscle. The relative proportion of these components varies with gender, genetics, age and lifestyle and can be indicative of overall health and fitness.

Two-component model - the amount of fat and fat-free mass of which the body is composed.  Fat-free mass is primarily composed of bone, muscle, vital organs, and connective tissue.

Chemical model - fat, protein, carbohydrates, mineral, water

Anthropometry – quantitative measurement of body size and proportions, for purposes of understanding human physical variation and body composition. Methods include skinfold thicknesses, circumferences, bony widths and lengths, height, and body weight.

Why assess body composition?

·  Determine optimal body composition for performance in sports

·  Develop sound weight reduction programs

·  Determine bone mineral content in women and children

·  Monitor changes in body composition associated with disease.

·  Track goals for weight management and strength training

·  Determine body composition related health risk

Co-morbidities/Complications Associated with Obesity

Type II diabetes mellitus

Hypertension

Coronary artery disease, and heart failure

Higher incidence of certain cancers – breast, colon, esophagus, prostate, kidney, and uterus.  Up to one-third of common cancers in industrialized nations are related to excess weight and diminished physical activity.

Dyslipidemia

Higher levels of inflammatory markers in the body

Stroke

Sleep apnea

Gallbladder disease

Nonalcoholic fatty liver disease

Osteoarthritis of the weight-bearing joints

Gout

Reduced fertility

Impaired obstetric performance

Reduced physical agility

Co-morbidities/Complications Associated with Excessive Thinness

Fluid-electrolyte imbalances

Osteoporosis

Bone fractures

Muscle wasting

Cardiac arrhythmias and sudden death

Peripheral edema

Renal disorders

Reproductive disorders

Eating disorders - is a disturbance in eating behavior that jeopardizes a person’s physical or psychological health.

·  Anorexia nervosa

·  Bulimia nervosa

·  Binge eating disorder

·  Female athlete triad

I. Essential Fat vs. Storage Fat

Essential fat - fat that is required for normal physiological functioning - structural components of cell membranes, required for the synthesis of certain hormones, transport of fat-soluble vitamins, etc.

Storage fat - fat that is stored in adipose tissue for energy supply purposes.  It is located underneath the skin, in the abdominal cavity, and around certain organs.

II. Body Composition of Males vs Females

The average male is taller, heavier, has a larger muscle mass, and a lower total body fat content.

For reference male and female, age 20 - 24:

  Storage fat - female = 15%

                   - male = 12%

  Essential fat - female = 12%

                       - male   =   3%

Female has sex specific fat in the breasts, pelvic and thigh regions.

The additional essential fat in females most likely serves biologically important functions for childbearing and other hormone-related functions.

"Male type" (android) obesity - excess fat is deposited on the upper torso and around the abdomen – apple shape.  Male type obesity is associated with higher health risks.

"Female type" (gynoid) obesity - excess fat is deposited below the waist in the thighs, hips, and buttocks (ie) pear shape.  After menopause females begin depositing more fat in the abdominal area

III.  Obesity

The combination of diabetes and obesity is one of the largest epidemics the world has faced.  The prevalence of overweight and obesity is increasing around the world and the obese are becoming more severely obese.

Obesity now ranks as the second leading cause of preventable deaths in the USA – about 330,000 deaths yearly.  Deaths from tobacco use ranks first.  Obese individuals with a BMI of 30 or larger can expect about a 7 year decrease in longevity.  Survival rates progressively increase as BMI decreases.

Obese children become obese adults.  Obese children at ages 6 to 9 have a 55% chance of becoming obese as adults – a risk 10 times than that of children of healthy weight. An obese child costs the health care system about three times more than a child of normal weight.

In the past dozen years, scientists have discovered that adipose tissue is not simply a passive storehouse for fat, but an endocrine organ that secretes more than a dozen peptide and non-peptide compounds that trigger changes throughout the body.  When fat cells expand they release more of some of these compounds and less of others.  Examples – leptin, adiponectin, inflammatory proteins, etc.

Causes of the Obesity Epidemic

1. Weight gain and obesity occur when energy intake exceeds energy expenditure – too much food and too little activity.  For most of human history, survival meant avoiding starvation – our bodies are set up to deal with scarcity, not abundance.  The average man and woman in the USA now consumes an average of 445 more calories daily than in 1970.

2. Decreased physical activity – automobiles, increased crowding, crime patterns, technological advances and automation in the home and the workplace, many hours spent watching TV, playing video games, sitting at the computer

3. Increased consumption of calories – consumption of large portion size meals, high-fat diets, high sugar intake

4. Social environment – advertising, pressure to consume, influence of family and friends

5. Genetics – the epidemic of obesity is occurring on genetic backgrounds that have not changed, but it is now clear that genetics plays an important role in the development of obesity.  One’s genetic makeup doesn’t necessarily cause obesity, but instead lowers the threshold for its development because of the impact of susceptibility genes.

Data from overfeeding experiments with identical twins demonstrate that some individuals are more at risk than others to gain fat when energy intake surplus is maintained at the same level for everyone and when all subjects are confined to a sedentary lifestyle.

NEAT – non-exercise activity thermogenesis.  It is the energy expended by physical activities other than planned exercise – sitting, standing, walking, fidgeting, etc.  In a recent research study, obese participants were seated for 164 minutes longer per day than were lean participants.

6. Role of viruses?  Do some viruses play a role in the expansion of adipose tissue mass?  This is a new area of research.

V. Body Composition and Aging

Changes associated with aging in a prosperous, industrialized society:           

·  increased fat mass

·  decreased muscle mass - sarcopenia

·  decreased bone mass

These changes can be slowed down by a regular exercise program and proper dietary habits.

Evidence indicates that skeletal fragility in elderly women is related to failure to obtain an optimal level of bone mass during childhood.

IV. Common Techniques for Assessing Body Composition (Anthropometry)

Direct methods - chemical analysis of human cadavers

Indirect methods - noninvasive techniques used on living persons

A. Height - Weight Tables

Desirable weight with regard to the lowest death rates is predicted from tables that have been developed by insurance actuaries.

Criticisms:

(1) These tables do not consider body composition.

(2) Most of the data in the 1983 Metropolitan Life Insurance Height-Weight tables comes from white, middle-class, U.S. adults age 25 to 59 years.  This is not a representative sample of the general North American population.

(3) No accepted method has been devised for determining frame size.

B. Body Density and Volume Measurements

Density = mass/volume.   Body density will vary with the amount of body fat. 

Use underwater weighing or volumetry to measure body volume. In recent years the UWW technique has begun to be replaced by air- displacement plethysmography (BOD POD method) where the subject is immersed not in water but in a closed air-filled chamber (plethysmograph).  Measure the volume of air displaced inside the closed chamber.

After body density has been determined using one of the above methods, use an equation, such as the equation developed by Siri, to determine percent body fat. 

These equations make two basic assumptions:

(1) The human body has two compartments - fat and nonfat

(2) Each of these compartments has densities which are known constants.  Assume that fat has a density of 0.90 g/ml and nonfat a density of 1.10 g/ml.

For decades hydrostatic weighing has been used as a universal method for validating skinfold caliper formulae and all other methods (ie) it has been used as the "gold standard".

Problems:- cadaver studies (Brussels cadaver study, 1984) have shown that the density of the nonfat compartment varies as a function of age, sex, and racial group. 

Therefore, a nonfat density value of 1.10 g/ml is not universally applicable.

Conclusion - densitometry should not be used as a universal criterion for prediction of percent fat. Equations based on four component models are preferred over equations based on a two component model.

C. Weight - Height Indices

Body Mass Index (BMI) - used as an indicator of obesity.  This index uses the body mass (kg) divided by the height (meters) squared.

Classification system for adults (20-70 years old):

BMI less than 18.5 = underweight

BMI of 25.0 to 29.9 = overweight

BMI of 30 or higher = obese

The absolute value of BMI is not used to classify weight status in children because change in BMI is normal and expected as children grow and develop.  In children, 2 to 19 years of age, a BMI between the 5^th and 84^th percentiles is healthy, between the 85^th and 94^th percentiles is overweight, and at or above the 95^th percentile is obese.

Recent research evidence indicates that these BMI cut-off points may need revision because the relationship between BMI and body composition, and between indices of fat distribution and the actual amount of visceral fat, differs across ethnic groups.  For example, Asian populations have a higher body fat percentage at a lower BMI compared to Caucasians.  Change the definition for overweight for Asian populations from 25 to 23?

A 2007 study in Vancouver found that, for the same amount of total body fat, Chinese and South Asian people had a far greater concentration in their inner abdomen, where it poses the greatest risk for diabetes and heart disease.

The main assumption of BMI guidelines is that BMI is closely associated with body fatness and consequent morbidity and mortality. However, some individuals who are overweight are not over-fat.

Criticism - BMI does not differentiate body composition.

BMI of NFL football players: Marshawn Lynch = 32.1, Ray Lewis = 33, Nick Mangold = 36.6

BMI of NHL hockey players: Sidney Crosby = 27.8, Alexander Ovechkin = 28.8

Accumulating research evidence shows that waist circumference and/or waist-to-hip ratio may be a better predictor of obesity related health risks than BMI.

The prevalence of overweight and obesity amongst Canadian children and adults has increased significantly in the past 20 years. 

D. Waist Circumference

WC has been shown to be a simple and inexpensive, yet effective way to assess for central obesity, with excellent correlation with abdominal imaging (CT and MRI), and high association with CVD risk and mortality.

One problem is that different research studies have used up to 8 different locations for measuring WC.  North American agencies now recommend performing the WC measurement at the iliac crest.

E. Skinfold Measurements

Read pages 4-1 to 4-3 in Laboratory Manual

Rationale - a relationship exists between the fat located in the depots directly beneath the skin and internal body fat and body density.

There are basically two ways to use skinfolds:

(1) Use the sum of a number of skinfolds as an indication of relative fatness among individuals.  Also compare "before" and "after" in the same individual.

(2) Use skinfolds in conjunction with equations or tables to predict percent body fat.

Skinfold caliper formulae to predict percent fat are site and sample specific.

Assumptions in using skinfold measurements to predict percent fat:

(1) Constant densities in a two-compartment model

(2) Proper identification of measurement site and proper measurement technique

(3) Constant compressibility of the skinfold

(4) Fixed adipose tissue patterning

(5) Fixed proportion of internal to external fat

There are two types of body composition prediction equations:

(1) Population specific equations - developed from relatively small, homogeneous (age, sex, state of training, fatness) samples.  Their application is limited to that subsample.

Example – Yuhasz

(2) Generalized equations - developed from large, heterogeneous samples.  These equations have a wider application in terms of age, and fatness.  However, these equations should be used cautiously with unique populations such as extremely obese individuals and professional football players.

Example - Jackson and Pollock, Durnin & Womersley, Peterson, Wang

With advancing age, proportionately more fat deposits internally rather than subcutaneously.  The same skinfold score reflects a greater total percentage of body fat as one ages.  For this reason, age-adjusted percent fat prediction equations are needed.

Even when the correct equation is used and the measurements are performed correctly, prediction of percent fat from skinfold measurements has an error of approximately 3-4 %.

F. CSEP-PATH Body Composition Assessment (CSEP – Canadian Society for Exercise Physiology)

Refer to Unit 6 in Lab Manual

In the CSEP-PATH body composition assessment procedures the Sum of Five Skinfolds has been removed in favour of the combined use of Body Mass Index (BMI) and Waist Circumference (WC) to provide an assessment of an individual’s health risks associated with body composition. 

The CSEP-PATH procedure first determines whether or not the subject is overweight or obese via a BMI calculation, then via the waist circumference measurement, if there is excess body fat deposited in the abdominal area. 

G. O-Scale System

Refer to Unit 5 in Lab Manual

Adiposity rating, proportional weight rating, stanine scale

H. Bioelectrical Impedance Analysis

Electrical impedance units are used to measure the electrical resistance of the body.

Impedance is greater in adipose tissue (14 - 22% water) than in bone and muscle (71 - 75% water).

Attach electrodes to the subject.  A low level electrical current (500 to 800 microamps at 50 kHz) is passed through the subject’s body.  The higher the electrical resistance, the fatter the subject.

The daily fluctuations in water content from exercise, dehydration, eating and drinking all need to be standardized to obtain optimum impedance results.

Clients must adhere to strict pretest guidelines in order to yield valid estimates of their body composition.

The prediction equations that estimate fat free mass are validated using underwater weighing.

These equations tend to overestimate fat mass in the lean and underestimate fat mass in the obese

Must use equations specific to given populations – sex, age, race, ethnicity

Error in percent fat estimation - approx. 3-5% body fat

I.  Other Procedures

1. Dual energy X-ray absorptiometry (DXA) – widely used for performing bone mineral density measurements.  It can also reliably and accurately quantify fat and regional lean body mass

2. Computerized tomography (CT) – the radiation dose is not insignificant.  Do the ends justify the means?

3. Magnetic resonance imaging (MRI)

4. Total body water - hydrometry

5. Ultrasound

6. Total body potassium

7. Near-Infrared Interactance (NIR)

CT, MRI and DEXA are now frequently being considered as “gold standards for calibration of field methods designed to measure adipose tissue and lean body mass.

CT, MRI and DEXA can distinguish between subcutaneous adipose tissue (SAT) and adipose tissue located in the abdominal cavity – visceral adipose tissue (VAT).   Although waist circumference is generally a good predictor of abdominal adiposity, it cannot distinguish between SAT and VAT.

These laboratory/research methods are accurate but they are expensive, cumbersome, and require highly trained technicians.

Conclusion - results of estimation of body composition should be interpreted cautiously.