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Comparing the Performance of Human Body Fat Measurement Devices

Researched by Caitlin H. 


The purpose of this experiment was to compare the performance of body fat devices on humans.

I became interested in this idea because I have an interest in human health and appearance.

The information gained from this experiment will help athletic trainers, nutritionists, etc. to determine the legitimacy of these devices. 
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My hypothesis was that the skinfold measurement would be more accurate than the circumference measure. 

I base my hypothesis on Richard T. Cotton, the editor of "Personal Trainer Manual", who says that the skinfold method is commonly used and is more accurate compared to other measurements. 
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The constants in this study were:

  • The same device to measure
  • The same amount of measurements on each person
  • The same area on each person measured will be measured
  • Dress of subjects
  • Age (11-13)  of all subjects
The manipulated variable was the measurement devices used. 

The responding variable was the reported percent of the body fat measuring devices.

To measure the responding variable I compared the reading from the two devices.  
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1 skinfold caliper

paper tape
5 boys dressed in shorts and T-shirt
5 girls dressed in shorts and T-shirt
1 data table
1 fitness trainer
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1) Have the subject dress into shorts and a T-shirt in a private area. 
2) A fitness trainer administers the tests individually to each student. 
3) Measurements are taken with the electronic skin fold caliper on the bicep, tricep, back, and above the hip. 
4) Once trainer finishes measuring in those areas write down what it says on the machine because it calculates all of the results and converts to body fat percentage. 
5) Then measure the body circumference in inches on the girls with a paper measuring tape of the abdomen, thigh, and forearm. 
6) Then measure the body circumference in inches on the boys with a paper measuring tape of the upper arm, abdomen, and forearm. 
7) Then convert the measurements to constants using "Table 5-1" and use this formula Constant A + Constant B ? Constant C ? 22.6 for girls or 14.2 for boys.  Record results, but not the student’s name. 
8) Repeat steps 1-7 for the rest of your subjects. 
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The original purpose of this experiment was to compare the performance of body fat devices on humans.

The results of the experiment show that on average for boys the skin fold test (11.4% body fat) was very similar to the circumference test (11.2% body fat).  For girls the two tests were not in agreement.  The skin fold test showed an average of 19.6% body fat while the circumference test showed readings of 10.1% body fat.  According to other researchers in the medical field, the higher value for girls would be expected.  The circumference test for girls was far too low when compared to national statistics.

See the table and graph.

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My hypothesis was the skin fold measurement would be more accurate than the circumference measure.

The results indicate that this hypothesis should be accepted.  According to experts, the body fat percentage for healthy girls should always be above 15% and boys should be above 5%.  This was true for the skin fold measurement. It was not true for girls, using the circumference method.  In fact it was off by nearly a factor of 2.  This is too big of an error.

Because of the results of this experiment, I wonder if other body fat measuring devices, especially those using the bioelectrical impedance method, would be more accurate.  It would also be interesting to know if the hydrostatic weighing would be more accurate compared to all of the other body fat weighing methods because people pay lots of money to have their fat measured and if it is not accurate then you wouldn’t want that method used on you.

If I were to conduct this project again I would use more subjects because the results could be different with 10 or 15 of each gender instead of 5.  Also, if larger people would have had their body fat measured the results could be different because some of the larger people do have a lot of fat and some have just more muscle. 
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Fat is a very important source of energy for the body.  It is one of the three main classes of nutrients.  There are many ways of measuring body fat, they are hydrostatic weighing, circumference measures, skin fold, and bioelectrical impedance.  Excess body fat has undesirable health consequences. 

Fat is one of the three main classes of nutrients that provides energy to the body.  Others are carbohydrates and proteins found in animals and plants, composed of carbon, hydrogen and oxygen.  Body fat is the most concentrated source of food for energy.  It supplies more than twice the calories by weight as protein or carbohydrates.  Fat provides essential fatty acids, which are necessary for proper functioning in cell membranes, skin, hormones, and transporting fat-soluble vitamins.  Each pound of body fat supplies 3500 calories and glycogen stores 2500 calories.  Fat (fatty acids) and carbohydrates (glucose) are two substances of the body’s cells used to produce most ATP (adenosine tri-phosphate ? energy source) supply.  Proteins are not a preferred energy source. 

Skin is an organ that covers bodies on humans and animals and protects the body.  Skin is almost waterproof and prevents the escape of fluids that bathe body tissues.  It prevents bacteria and chemicals entering parts of the body, so it is an important part of body defense against diseases.

The liver produces digestive fluid called bile.  It helps process carbohydrates and amino acid.  The liver converts the surplus glucose into animal starch, glycogen.  The liver stores glycogen for re-conversion and releasing it as glucose at a later time of need.

Glycogen is a carbohydrate that is a tasteless, odorless, white powder.  It is made up of units of simple sugar called glucose, linked together in branched chains.  Glycogen is formed and stored in the liver and muscle.  It is made of excess starch and sugars in the body.  The starch and sugars are first converted to glucose.  The excess glucose is then changed to glycogen.  Glycogen, called animal starch, stores food easily and is quickly reconverted to glucose.  In the muscles and liver the glycogen is converted to glucose when the body needs energy.

Body Fat Percentage 
The body fat percentage in a healthy human ranges 5-40%.  Females seldom have less then 15% body fat; males seldom have less than 5%.  Athlete’s body fat varies depending on the sport.  Distance runners tend to have low fat content.  Most humans have too much fat; others get carried away trying to achieve unrealistic, unhealthy, low levels.  Excess dieting can cause loss of muscle mass and strength along with fat. "Excess body fat has been associated with a number of health risks, including heart disease, diabetes, hypertension, arthritis, gall bladder disease, cirrhosis of the liver, hernia, intestinal obstruction and sleep disorders," according to Richard T. Cotton.  
Bioelectrical Impedance 
Bioelectrical impedance is based on the principle that the conductivity of an electrical impulse is greater through lean tissue than through fatty tissue.

Hydrostatic Weighing 
Hydrostatic weighing is the body fat percentage calculated from body density.  It is a water-weighing test considered "gold standard" body composition assessment. 

Circumference Measures 
Circumference measures are easily used to assess body composition. You must use the exact anatomical landmarks.  The cloth or metric measurement tape is pulled tight enough to keep the position with out causing indentation in the skin. 

Skin fold 
The skin fold measurement is based upon the sum of the three specific sites. The test should not be taken after exercise because the transfer of fluid to the skin is a result of over estimations.  Of the many equations estimating body composition; two developed by Jackson and Pollock (1985) have the smallest margin of error for general population. 

After hydrostatic weighing, the two most accurate ways of measuring body fat are the circumference measure and the skin fold.  Body fat content is very important to overall health. 
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Andre. "Glycogen," The World Book Encyclopedia. 1998 vol. G. pp. 237

"Body Fat Percentage." [Online] Available, October 16,2000

Cotton, Richard T. Personal Trainer Manual. pp. 7, 130, 182 - 187, 189, 192,Dubois, 

"Fat," The World Book Encyclopedia. 1998. vol. F pp. 52

"Liver’s Role," The Human Body. vol. 7 pp. 31

Rath, Karlyn. fitness trainer. Yakima, Washington (tested 1/12/01)

"Skin," The World Book Encyclopedia. 1999. vol. S-SN pp. 488 
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I would like to thank Mrs. Rath for taking all of the measurements in my experiment.  She had to take time off work to come and take the measurements of the ten, seventh grade students.  She also got the caliper that I used for the skin fold measurements. 

I would also like to thank the IRB committee for passing my project.  If they wouldn’t have I don’t know what I would have done.

I would like to thank Mr. Faringer because he was a big help for getting all of the measuring tapes that I used to measure the circumference of the human. 

I would also like to thank Mr. Newkirk and Mrs. Pasckvale for helping me with the whole project. 

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