BODY COMPOSITION

Body Composition

Reasons to measure body fat:

a) increased risk of coronary artery disease

b) non-insulin dependent diabetes

c) hypertension

d) increased incidence of certain types of cancer

Important to measure lean body tissue as well

a) muscle wasting (sarcopenia)

b) osteoporosis

Body Composition

Overfatness factors

1) decreased caloric output (decreased activity)

2) increased caloric input

3) genetics: hyperplasia,

hypothyroidism (decreased adipose beta receptors)

Some of the hormones released by adipocytes include adiponectin and resistin. Decreases in resistin related to insulin resistance. Hormones decreased with obesity.

Leptin release decreases with rapid lipolysis

Leptin

• The fat hormone leptin works in the brain to trigger the nerve cells that control eating. In the medial hypothalamus, leptin activates "anorectic" nerve cells, which release appetite-suppressing neuropeptides (POMC and CART). At the same time, leptin inhibits another group of leptin-sensitive nerve cells, called "orexigenic," which release appetite-regulatory neuropeptides (NPY and AGRP). The two groups of leptin-sensitive cells send appetite-suppressing signals to key nerve cells in the lateral hypothalamus thought to control several behaviors including feeding (ORX and MCH).

Resistin

• Ability of adipokines such as resistin to directly modulate endothelial function and incite endothelial activation may represent an important link between insulin resistance and cardiovascular disease. Verma S, et al. Circulation. 2003 Jul 21

Resistin

Body Composition

Changing Body Composition

1) increase caloric output

– a) increase frequency, volume and intensity (myth of fat burning exercises)

– b) increase lean tissue (resistance training)

– c) multiple training sessions to increase EPOCs

2) decrease caloric intake (excessive decrease signals leptin release)

Energy Requirements

• Determined by:

• Resting metabolic rate (60-75%)

– Genetics can change this factor by 10-20%

• Thermogenesis (7-10%)

• Physical activity

• Growth

• Factors modulated by age, size, genetics, environmental temperature, training conditions

Decrease body fat

3) increase water intake

4) increase roughage and eat roughage first with a meal

Body Composition

5) multiple small meals to decrease insulin response

6) eat before exercise (will be used as substrate)

7) eat as soon as possible (within 1 hour) after exercise

(increased Glut 4 activity after exercise increases storage of glycogen)

8) Eat a combination of CHO and protein to facilitate CHO storage.

8) Diminish full glycogen storage (decreases lipogenesis)

Need higher

intensity exercise

rather than low

intensity

Body Composition

Multi-Level Intervention Strategy

• goal setting based on initial fitness and desired outcomes

• identifying personal costs and expected barriers to adoption and maintenance of an activity

• developing strategies for eliminating or minimizing the impact of barriers to participation and for increasing support and reinforcement from friends, family, and housemates.

Body Composition

Multi-Level Intervention Strategy

• planning a gradual progression of difficulty to optimize success and facilitate self-efficiency so clients have growing confidence in their physical ability to be active and to maintain the new pattern of activity.

• Offering feedback from fitness testing and clients’ self-monitoring of activity and progress

• developing clients’ personal strategies for returning to activity after inactivity due to flagging motivation, injury, vacation, and so forth.

Body Composition

• Over 100 different equations for estimating body composition

• Direct Methods: dissection, chemical analysis, MRI, Indirect Methods: Property and/or component based

– Property: measures body volume (hydrostatic), decay properties of isotopes (total body water from tritium dilution), air displacement plethysmography, dual energy X-ray absorptiometry

– Component: ratios of measurable quantities to assumed constant components within and between individuals (i.e. derive FFM from TBW)

Direct Methods

• Magnetic Resonance Imaging

• Body is placed in a strong magnetic field resulting in some of the hydrogen protons becoming realigned.

• When magnetic field is turned off, hydrogen protons lose their alignment and release energy. This energy release is monitored and displayed along length of body

Direct Methods

• Computed Tomography (CT)

• Uses x-rays passed thru the body with detectors on other side of body to monitor transmitted radiation

• Transmitter rotates 360 degrees around body along length of body

• More accurate determination of visceral adipose than MRI

• Disadvantage is the radiation dose

Compartment Models

• 2 compartment model

= body fat and fat free mass (FFM)

Hydrostatic weighing (UWW), ⁴⁰K counting and radioactive water dilution

All assume constant concentrations of 0.732 l/kg of body water and 68.1 meq/kg of body K

Fine for healthy young white adults

Compartment models

• 3 compartment model

• Includes UWW with a measure of total body water by isotopic dilution method

• FFM divided into water and remaining solids (mostly proteins and minerals)

• Better prediction but not accurate for patients with depleted bone mineral mass

Compartment models

• 4 compartment model

• Provides measures of protein and minerals thru neutron activation analysis (less than 10 in the world) and dual energy x-ray absorption respectively

• Assumed values are 1.34 and 3.075 kg/l for protein and mineral respectively

• Approximation of mineral content over short term acceptable since mineral content does not change appreciably in the short term.

Mineral analysis

• Insert table from p.668

5 compartment model

• Insert figure p. 80

Body Composition

• Hydrostatic Weighing (UWW):

– assumption: adipose tissue density = 0.9 g /cm3

– assumption: lean tissue - 1.1 g /cm3

– considerable variation between individuals

– Uses a 2 compartment model: 1 part fat and 1 part fat free mass (too simplistic!!)

• Residual volume estimates may increase standard error by up to 300% (i.e. 1.3% calculated as 4.1%)

• Test retest correlation - 0.98 with a standard error of 1.2%

Body Composition

• Considerable variation due to body hydration, protein and mineral content

• Typical error = 3-4% of body weight

• Brozek Equation:

– Percent fat = (4.57 / body density - 4.142) x 100

Based on pressure-volume relationship
Same assumptions as UWW
Advantage over UWW is no need to hold breath underwater

Body Composition

– Double Indirect: skinfolds and bioelectrical impedance use regression equations to compare a known component to an unknown component requiring a combination of equation methods

– BIA: aqueous tissues are conductors while fat and bone are poor conductors

• Problems are that not all tissues are electrically isotopic

– Body is not a perfect cylinder as assumed by the equation

Bioelectrical Impedance Analysis

Bioelectrical Impedance Spectroscopy

• A more complex model than BIA which partitions body into a series of cylinders

• Resistance and reactance measures are made over a range of frequencies

Total Body Electrical Conductivity

• Based on premise that when body is placed inside a coil that is used to generate a time varying electromagnetic current, eddy currents are induced in the body.

• This causes a perturbation in the external field resulting in the absorption of a small of energy which is dissipated as heat

• Info collected at 64 locations along length of the body

Other Double Indirect Measures

• BMI

• Waist girth

• Waist to hip ratio

• Skinfolds

Body Composition

Skinfold Methods:

• Sloan Weir

– men: thigh and subscapular

– women: triceps and suprailiac

– Men: Density = ~ . ~ 043 - (0.00133 x thigh) - (0.001~ ~ x subscapular)

– Women: Density = 1.0764 - (0.00081 x suprailiac) - (0.00088 x triceps

– Limitation: more appropriate for individuals under 30

Body Composition

Skin fold measurements

1) Sloan-Weir Method (1970)

• Formula developed by relating skinfold thickness in young men and women (17-26) to body density determined by hydrostatic weighing

Body Composition

2) Durnin - Womersley Method (1974)

• Tests were done on people from 16 - 72 years

• Skinfold sites

– Men and Women –

– Bicep (vertical fold on the anterior surface of the upper arm at the level of the triceps skinfold)

– Triceps (Vertical fold half way between the olecranon process of the elbow and the acromion process of the shoulder)

– Sub-scapular (2 cm directly under the inferior angle of the scapula)

– Iliac Crest (diagonal fold running downward and anteriorly, raised directly above the iliac crest at the mid axillary)

Body Composition

• Limitations - At the lean end of the scale, the calculated percent fat increases considerably for only small increases in skinfold thickness and fat is over predicted at the lean end

Body Composition

3) Jackson - Pollock Method (1978 and 1980)

• Tests done on people with age ranging 16 - 61

• Skinfold sites

– Triceps (Vertical fold half way between the olecranon process of the elbow and the acromion process of the shoulder)

– Sub-scapular (2 cm directly under the inferior angle of the scapula)

– Suprailiac (diagonal fold running downward and anteriorly, located 7 cm above the spinale on the line from the anterior axillary border to the spinale of the illium, on the man chart it is located approximately 3 cm to the medial side of the iliac crest skinfold)

Body Composition

– Front Thigh (vertical fold on the front thigh, halfway between the the patella and the inguinal crease with the foot placed on a 20-30 cm high bench, and the leg relaxed)

– Chest (diagonal fold taken halfway between the anterior axillary line and the nipple for men and one-third of that distance for women)

– Axilla (vertical fold on the mid-axillary line at the same level of the xiphoid process of the sternum)

– Abdominal (vertical fold taken about 2 cm to the right of the umbilicus cord)

Body Composition

• There are six different predictive equations. Each one uses all or several of the skinfolds.

• Limitations - Prediction of body fat for women over the age of 40 may not be accurate

Body Composition

4) Yuhasz Method (1966)

• The original subjects used were college aged students

• Skinfold sites : Men and Women

– Front Thigh (vertical fold on the front thigh, halfway between the the patella and the inguinal crease with the foot placed on a 20-30 cm high bench, and the leg relaxed)

– Chest (diagonal fold taken halfway between the anterior axillary line and the nipple for men and one-third of that distance for women)

Body Composition

– Triceps (Vertical fold half way between the olecranon process of the elbow and the acromion process of the shoulder)

– Sub-scapular (2 cm directly under the inferior angle of the scapula)

– Abdominal (vertical fold taken about 5 cm to the right of the umbilicus cord)

– Iliac Crest (diagonal fold running downward and anteriorly, raised directly above the iliac crest at the mid axillary) The women must substitute rear thigh for the chest skin fold.

Body Composition

– Rear thigh (vertical fold on the posterior thigh at the same level as the front thigh skinfold with the leg in the same position as the front thigh)

• Limitations - Validity is only limited to the college aged group

Body Composition

Determination of Optimal Body Weight

• Excess Fat = (% body fat - ideal % body fat) x weight Optimal weight = Body weight - excess fat

• Calculation of optimal weight questionable due to lean tissue changes

Body Composition

Normative Data for Yuhasz Body Fat Prediction Technique

Ideal Average

Males - college 9 12

- 16-30 yrs 8-12 10-15

* Note: male swimmers, wrestlers and basketball players are generally 4-7% fat

Females - college 13 16

- 16-30 yrs 16-22 21-28