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Inside CSULB
Vol 57 No. 16 : Sept. 1, 2005
Vol 57 No. 16 | Sept. 1, 2005
Profs See BOD POD as a Dry Alternative

Ralph Rozenek and James Davis

Department of Kinesiology's Ralph Rozenek (l) and James Davis.

Want to measure your percent body fat, but don’t want to get wet? In the not-so-distant past that couldn’t be avoided since the most accurate way to test for percent body fat always involved getting into a tank of water and blowing as much air out of your lungs as possible while going under water for about 20 seconds. Sometimes participants had to repeat the process up to five times to obtain accurate results. Not any more.

About three years ago, the Department of Kinesiology purchased something called a BOD POD Body Composition System, the latest commercially-available machine that measures a person’s percent body fat. The BOD POD itself has been in existence approximately 15 years and commercially available for about 10 years. Now, instead of going under water to be tested, a person simply puts on a tight-fitting swimsuit and bathing cap, then sits in the capsule-shaped BOD POD, a totally dry enclosure, to be measured. Like the tank test it still takes about four minutes, but you can leave your towel at home.

Since CSULB’s acquisition of its BOD POD, it has been used extensively in the laboratory components of select Kinesiology courses in exercise science. More than 500 tests have been completed, the majority of those under the guidance of Ralph Rozenek and James Davis, professors in the Department of Kinesiology.

“I think one big advantage is that you can use the BOD POD for a variety of populations such as children and the elderly,” said Rozenek, who secured the unit mainly for student laboratory and research purposes. “You may have younger children, but now you can test them if they have a fear of water. If there is someone in a wheelchair, it’s possible to get them into a BOD POD fairly easily and do some testing.”

“Now you can have somebody who is really very ill, someone who is undergoing chemotherapy or is even hospitalized, and they can do this test,” said Davis. “Whereas before, they certainly couldn’t do underwater weighing. You wouldn’t want someone to have a heart attack, especially under water.”
It’s common to hear about the low body fat measurements of endurance athletes, especially those at the world-class level, but why would average individuals want or even need to know how much body fat they have?

Simply, if someone has too much or too little body fat it can be unhealthy. Too much body fat increases the risk of many diseases, including type 2 diabetes, high blood pressure, stroke, heart disease and certain cancers. Too little body fat is linked to problems with normal functioning of the body and can lead to a number of health-related issues such as reproduction problems in women. People have an essential body fat which is the minimum percent body fat possible without incurring health problems. In men, the essential body fat is approximately 3-5 percent of body weight, while women have a higher percentage at about 8-10 percent.

Ralph Rozenek and James Davis

Just how does the BOD POD work?

While a person sits inside the enclosure, a rapidly vibrating diaphragm in the wall of the test chamber produces small changes in air pressure between it and an adjoining reference chamber. The changes in air pressure can be used to determine the amount of air the person displaces in the test chamber. In turn, that measurement leads to an estimation of the person’s body volume, corrected for the volume of air in the lungs at the time of the measurement.
Then, taking the person’s body mass (obtained by a scale) and dividing it by the person’s body volume, the body density is determined. With that, a person’s percent body fat can be calculated.

And though the underwater (hydrostatic) weighing is still considered the “gold standard” of the various methods available for estimation of percent body fat, studies performed in several research laboratories have shown that the BOD POD provides accurate measurements of percent body fat.
One key variable is lung volume measurement made by the BOD POD. To investigate whether the lung volume of those tested in the BOD POD was accurately measured, last semester Davis took a total of 100 college-aged males and females and measured their lung volume in the unit and in a separate room with a completely different instrument for measurement of lung volume. The result?

“I have done an initial analysis of the (lung volume) data and it’s almost identical in the different tests,” said Davis. “It validates that the lung volume measurement made by the BOD POD is accurate.”

“One of the things Dr. Davis has been looking at is the lung volume measurements,” said Rozenek. “For both underwater weighing and for BOD POD testing you have to take into account a person’s lung volume because any air that is in your lungs tends to make you float in water and have extra body volume in the BOD POD, so that will look like body fat. You somehow have to account for that. So far the BOD POD measurement of lung volume looks very comparable to standard techniques that measure lung volume.”

Those interested in having their body fat measured for a nominal fee can contact either Rozenek at 562/985-4083 or Davis at 562/985-8060.

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