Tests To Assess Body composition
In physical fitness, body composition is used to describe the percentages of fat, bone and muscles in human body. The percentage of fat is of most interest because it can be very helpful in judging health in addition to body weight. The most accurate assessment of your ideal weight takes into account the composition of your body ? how much of your weight is lean body mass (muscle and bone) and how much is body fat. For optimum health, body fat should be no more than 20% of total body weight for men and 30% for women. Fat is produced by the body when an excess intake of calories from food,alcohol, soft drinks etc. When the diet provides the body with more calories than it needs for general maintenance and its current level of physical activity, this excess energy is stored in the form of body fat.
Fat is stored in two primary ways -- deep in the body cavities, and directly beneath the skin (called subcutaneous fat. Female pattern obesity emphasizes subcutaneous fat. But most men have little room to boast, and good reason to keep quiet. The reason is, male pattern obesity emphasizes deep fat storage, which accumulates and pushes against the abdominal muscles, stretching them. (This causes many men to incorrectly assume that because their protruding bellies are hard, they are not fat. This is an incorrect assumption.)When you wear a lot of fat around your waist, you take on the shape of an apple. This is called male pattern (also android or abdominal pattern) obesity. Females tend to store fat on the hips thighs and buttocks, giving them more of a pear shape. This female pattern is also called gynoid, or gluteal-femoral pattern obesity. The apple shape is not necessarily restricted to men, although it is most prevalent in males. Similarly, the pear shape is not restricted to women. This following test will assist you to assess body composition.The following are examples of body composition tests:
Bio-electrical impedance fat percentage
Skinfold caliper test
Body mass index
Near infrared spectrophotometer
Dual energy x rays absorptiometry
Hydrostatic weighting also known as underwater weighing scale is the standard against which other methods of body composition estimation are based.
Bone mineral is more than dense than muscle tissue, which is more dense than fat.
Hydrostatic stainless steel weighing tank, Underwater mounted chair and scale, weighted belt,
• The dry weight of subject is first determined. The subject should be wearing minimal clothing, then sits on a specialized seat, expels all the air from his lungs.
• Then subject is lowered into the tank until all body parts are emerged. (Person has to stay motionless during process) underwater body weight is recorded.
• Body density is calculated from the relationship of normal body weight to underwater body weight. And then body fat percentage is calculated from bone density.
• In this method of body composition, residual lung volume should be physically measured,RLV calculated from mathematical formulas gives you error.
Body density = Wa/ (((Wa-Ww)/Dw) ??- (Rv + 100cc))
Wa = body weight in air(kg) , Ww = body weight under water(kg) , Dw = density of water , Rv = residual lung volume ,
And 100cc is the correction = for air trapped in the gastrointestinal tract.
Calculated body density can be converted to body fat using following formula.
Percentage of body fat = (495/body density) - 450
1) It is often impractical in terms of expense, time and equipment.
2) Measurement of residual volume of air in lunges.
3) Interindividual variability in the amount of air in the gastrointestinal tract .
4) Interindividual variability in the density of an individual lean tissue compartments.
5) Final result may include 2% to 3 % error in the estimation of percent body fat.
Bio electrical impedance
Conductivity of an electrical impulse is greater through lean (eg-muscles) tissue than through fatty tissue. The bioelectrical impedance device measures the resistance of body tissues to the flow of a small electrical signal. The proportion of body fat can be calculated as the current flows more easily through the parts of body that are composed mostly of water(muscles, blood etc) than it does through fat and bone.
A bioelectrical impedance analyzer.
• Bioelectrical impedance analyzer have four electrodes, they apply current of 500 micro Amps (harmless to human body) at a single frequency of 50 Khz or more.
• With tetrapolar configuration, two electrodes inject the current while other two electrodes sense the emerging current.
• Arrange subject atleast 50 cm away from any electrical devices, with subject's arms not touching their trunk, thighs should not touch each other.
• Ask subject to remove any metallic objects, shoes and socks from their body.
• Then turn on the device and record the readings.
• Problems with regular BIA (bathroom scale) with bathroom scales may estimate subject's lower body composition. Because there are no electrodes attached to upper body.
• For appropriate skin preparation, site should be washed with alcohol.
• Human errors in electrode placements.
• It should not be taken immediately after exercise.
• Subject should not consume alcohol in the past 24 hours.
• This method does not provide consistent reading.
• It can be affected by body tempeature, time of the day and hydration state.
• People with pacemakers should not use bioelectrical impendence for body composition test.
• This method does take into account the location of body fat.
• The standard error associated with this method is 3.5% to 5% in the estimation of percent body fat.
Skinfold caliper test
Skinfold caliper testing is based on the assumption that the amount of fat present in the subcutaneous (underskin) regions of the body is 50 % of overall body fatness.
Calibrated skinfold calipers (Recommended name of the manufacturers eg.Harpenden, Holtain, Slimglide, Lange)
• Measurement can use from 3 to 9 different standard anatomical sites around the body. The right side is usually only measured.
• Locate the anatomical site to be measured and mark it with eyebrow pencil.
• Grasp the marked skinfold firmly with the thumb and index finger of left hand.
• Hold the caliper perpendicular to site, place the pads of the calipers approximately ? inches from the thumb and forefingers.
• Note down the reading to the nearest to 0.5millimeter.
• A minimum two measurements should be taken at each site, with atleast 15 seconds between measurements to allow the fat to return to its normal thickness.
• Continue to take measurement until two consecutive measurements vary by less than 1millimeter.
Anatomical locations (Right hand site)-
Thigh- A vertical skinfold taken midway between the hip and knee joints on the front site of thigh.
Triceps- A vertical fold on the back of the upper arm taken halfway between the acrominal (shoulder) and olecranon (elbow) processes.
Abdominal - A vertical fold taken 1 inch lateral to the umbilicus.
Suprailium - A diagonal fold taken at, or just anterior to, the crest of the Ilium.
Chest- A diagonal skinfold taken midway on the anterior axillary line (midway of underarm and nipple).
Calf - A point on the medial surface of the calf, at level of the largest circumference.
Common drawbacks -
• Improper site determination and measurements are the two primary sources of error.
• Skinfold measurement should not be taken after exercise because transfer of fluid to the skin could result in overestimations.
Body mass index
The body mass index was invented by the Belgian adolphe quetelet during the course of developing "social physcics".Body mass index method calculates body composition by taking person's weight (in KG) and dividing by their height (in METER) squared. The higher the figure more overweight you are. Remember BMI method to calculate body composition is just guide -it does not accurately apply to all populations.
weighting scale, meter scale to measure height and BMI Formula = Weight (kg)/height in meter square
• Note down total body weight (KG) of the subject.
• Measure height (in meter) of the subject.
• Calculate BMI using above formula.
• Compare the results with following
Common drawbacks -
BMI can be inaccurate because BMI formula considers the total body weight (not fat free mass), that includes fat and fat free mass. Using this formula large and muscular though lean athletes scores high BMI levels which incorrectly rates them as obese.
Near infrared spectrophotometer (NIR)
Near infrared spectrometry is developed by the United States department of agricultural to measure the body composition of livestock. It is based on assumptions different types of tissue in the body (e.g.fat tisue versus muscle tissue) have different optical propertities, introduction of a known light source, and subsequent measurement of its "reflection" from internal tissues, can be used to estimate overall body composition. This method of calculating body composition uses the principle of light absorption and reflexion to measure body fat.
• An emmi/sensor wand is placed over the site to be assessed (eg, the belly of the biceps).
• A low energy of an infrared light beam is emmited.The energy is either reflected, absorbed or trasmitted, depending on the scattering and absorption properties of the biceps.
• Sifts in the wavelength of the reflected beam and a prediction equation are used to compute the percentage body fat.
• The sensor in the wand detects the reflected beam.
Common drawbacks -
• Improper placement of wand.
• The standard error associated with this method is 4% to 11% in the estimation of percent body fat.
• This technique still lacks validation in humans.
• This method assumes fat in the arm is proportional to total body fat which may not be true.
Measurements of height, weights and girth provide information about the relative distribution of body mass compared with standard distributions.it is perhaps the easiest methods for assessing body composition.
Non elastic measurement tape.
Measuring circumference of the anatomical site and record it. And compare it with next measurements.
Abdominal - At the level of the umbilicus.
Hips- The largest circumference at the posterior extension of the gluteus.
Iliac - Level with the iliac crests.
Waist - The narrowest part of the torso.
Chest/breast- The largest circumference.
Bicep - The largest circumference.
Common Instructions -
Pull the tape tight enough to keep it in position without casuing an indentation of skin.
When assessing significantly obese client, be sure to use a long enough tape.
Tape should be periodically calibrated.
Bod Pod (Air displacement)
This method is developed by life measurements instruments, concord, CA.This method correlates with hydrostatic weighing but uses air instead of water. The bod-pod measures the volume of air a person's body displaces while sitting inside a comfortable chamber.
Bod-pod by life measurements instruments,concord,CA.
The bod pod system measures body composition by determining body volume and body weight, body volume is measured by first Measuring the volume of the chamber while empty. Then the volume of subject chamber is measured with the subject inside. By the subtraction the volume of the subject is determined. Body weight is measured using empty scale. Once those two variables are determined, body density can be computed and inserted into an equation to provide percentage of fat
• Operator note down total body weight in KG.
• Subject sits in the bod pod chamber for two 50 seconds measurements.
• Then lung volume is measure by two ways either using breathing tube or prediction.
• Body density can be computed and inserted into an equation to provide percentage of fat.
• Subject has to wear minimal clothing.
• A swim caps must also be worn to compress any air pockets within the hair.
• Subject has to wait minimum two hours after exercise because hydration status and increased muscle temperature effects adversly on results.
• It takes 5 minutes to complete the test.
• The bod-pod and hydrostatic weighing often produced identical results.but bod-pod is more easy.
Dual energy x rays absorptiometry.
DEXA machine differentiates body weight into the components of lean tissue,fat tissue and bone.based on the differential attenuation by tissues of two levels of x rays.
DEXA (dual energy x-ray absorptiometry)
• The person lays on the whole body scanner, with the x-rays sources mounted beneath a table and detector overhead. The person is scanned
• With photons that are generated by two low dose x-rays at different levels. The body's absorbtion of the photons at the two levels is measured.
• The ratios can be used to predict total body fat, fat free mass and total bone mineral. This procedure takes 12-15 minutes.
• One does not have to wear bathing suits( bod-pod method).
• There is no special preparation on the part of the participant.