The Exercise Physiology Laboratory at UNLV assesses body composition for people other than those who are serving as subjects in research studies.

The body composition evaluation consists of five different assessments:

1. Underwater weighing (hydrostatic weighing)

2. Bioelectrical Impedance

3. Skinfold measurements

4. Waist to hip ratio (Abdomen to gluteal ratio)

5. Body Mass Index (BMI)

The results are presented as:

1. Percent body fat

2. Lean body weight

3. Skinfold profile with comparisons to national norms based on age and sex.

4. Target weight based on 16% fat for men and 23% fat for women.

5. Athletic target weight based on 10% fat.

TEST DESCRIPTION

1. Underwater weighing (UWW). UWW is considered the gold standard for body composition assessment. It is the criterion method against which all other body composition measurements are compared. However, UWW is a laboratory techniques involving equipment costing approximately $70,000, it needs 2 or 3 testers and takes about 25 minutes. It also takes 1 hour of preparation prior to measuring and 45 minutes after the actual testing.

UWW is user friendly, except for individuals who are hesitant to submerge their head in water. The water is warm 93 degrees; the subject is sitting cross-legged "up-to-his/her neck" in the water on a scale bed, which is 2 inches above the bottom of the tank. A 20 lb. canvas jacket is worn which guarantees the subject will not float. The subject has a nose clip and a mouthpiece, which is part of a snorkeling system. There is a rebreathing bag fitted to the snorkeling system, which has 5 liters of 100% oxygen in it.

When ready, the subject leans forward putting his/her head on the knees, this leaning forward submerges the subject. The subject then stays there breathing air through the snorkel until the water settles down (usually takes 20-30 seconds). The subject (who can hear underwater) is told to blow out some air, just a comfortable amount. At that moment the snorkel is turned off and the subject cannot breathe through the snorkel, this usually takes 10 – 15 seconds; this is when the weight of the person in the tank is measured. Immediately the weight is recorded the snorkel system is opened to the rebreathing bag and the subject starts breathing oxygen in and out of the rebreathing bag. At this time the subject can raise the head out of the water, but still breathing in and out of the bag. After 8 breaths the bag is switched off and the subject starts breathing air again. That completes one weighing. The bag is then analyzed for nitrogen and the amount of air that was in the lungs at the time of weighing is determined. While that is being done the subject is weighed two more times.

The weight of the jacket and the volume of air in the lungs at the time of weighing are subtracted from the weight under water giving the true underwater weight.

2. Bioelectrical Impedance. Two electrodes are attached to the foot and two electrodes are attached to the wrist. A very low-grade electric current (from a 9-volt dry cell battery) is passed between the electrodes and the impedance (resistance) is measured in ohms. The subject does not feel the current at all. Then through equations total body water and percent fat is determined. This technique, using approved instruments, is very close to the results obtained by UWW. The technique takes 5-6 minutes and is done in a lying position.

3. Skinfold measurements. Skinfold measurements are taken in locations where fat typically accumulates. Abdomen, hips, arms and thighs. The measurements are taken with calipers, which measure the skinfold thickness in mm. These raw measurements represent the amount of subcutaneous fat in that location. These measurements can be compared to national norms based on age and sex and a profile can be drawn. Four of these skinfold measurements can then be put into an equation (the Jackson/Pollock equation) and percent fat determined. This equation has been validated against UWW and correlates .96 with UWW. Note: a trained technician who has proven test-retest reliability must take Skinfold measurements. The calipers must be constant tension springs, and the sites must be exactly the same as the norms to which they are compared. In the hands of a trained technician skinfold measurements and bioimpedance have about the same accuracy.

4. Waist to Hip ratio. There has been considerable scientific evidence that the amount of fat accumulation around the waist and hips is more dangerous (metabolic disease-wise) than fat elsewhere in the body. Waist to Hip ratio evaluates this fat accumulation. It is an easy-to-take measurement and is used extensively in epidemiological studies to describe the risk of metabolic disease in large populations. Example: if the waist girth were the same as the hip girth the ratio would be 1.0. Since the waist girth should be smaller than the hips, the ratio should always be less than 1.0. This is not a good measurement to monitor changes within an individual, but is good to classify an individual for health risk.

5. Body Mass Index (BMI). Body mass index is commonly used in epidemiological studies to determine the fatness of populations. It is a good measurement to classify an individual into a group based on fatness. It is not a good measurement to show changes within an individual.

INSTRUCTIONS & REQUIREMENTS

The complete evaluation takes approximately 30 minutes. Subjects should wear a swim suit (as brief as possible; a Speedo racing trunk would be better than boxer style swim suit). Bring a towel. You can change in the laboratory.

Guidelines:

Please be on time. See the map in this website, call if you need further directions

Cost of the evaluation: $150.00

If more than one person at the same time: $100.00 each

Checks should be made payable to: UNLV Board of Regents and are payable at the time of assessment.

If you cannot keep your appointment please call, there are 3 people waiting for you. 895-3766

Also please call if you have any questions.

Bioimpedance and skinfold measurements