Detailed Descriptions of Body Composition Methodologies

Anthropometry:

Anthropometric data include weight, stature, sitting height, trunk depth, circumferences of the midarm, abdomen, hip, mid-thigh and maximum calf and triceps, biceps, subscapular, midaxillary, suprailiac, mid-thigh and lateral calf skinfold thicknesses. All measurements are taken using techniques similar to corresponding measurements in the Anthropometric Standardization Reference Manual (Lohman, T., Roche A., Martorel, R., eds., 1988, Human Kinetic Books) or to corresponding measurements in NHANES III. All measurements are taken by two independent observers, and repeated measurements taken if the measurement difference between the observers is greater than a preset error limit. Anthropometry has been collected continuously in the Fels Longitudinal Study since 1929.

Dual energy x-ray absorptiometry (DXA):

Total and regional body composition measurements from DXA are made using a Lunar DPX with Version 3.6z total body scan software. The Lifespan Health Research Center is a beta test site for the Lunar advanced software for body composition analysis. DXA uses an 80 kVp x-ray tube with a K-edge filter (350 mg/cm2 of cerium) to generate x-ray beam energies as 40 and 70 keV. The information from a total body scan includes total body bone mineral (TBBM), soft-tissue attenuation ratios (Rst-values), fat and lean tissue weights (g), and percent fat for 9 body regions (head and neck, left and right thorax, para-spinal, pelvis, each arm, each leg), as well as, total body fat (TBF), percent body fat (%BF), fat free mass (FFM), and TBBM. In addition, a lumbar spine and hip scan is performed for participants over 50 years of age. The precision for in vivo measurement of TBBM has been reported as 0.5% and that of estimates of %BF for the body regions and for the whole body is less than 1.5%. This level of accuracy, however, is reported to be stable only for subjects with a sagittal thickness (trunk depth) of less than 27 cm. The errors of body composition estimates increase for obese participants who exceed this thickness. Sagittal thickness at the umbilicus is measured in all participants. Also, sagittal thickness has been reported to be highly correlated with internal and subcutaneous adipose tissue of the trunk. DXA has been used in the Fels Longitudinal Study since 1990.

Hydrodensitometry:

The underwater weighing apparatus at the Lifespan Health Research Center consists of a plastic chair suspended from four electronic load cells attached to a support frame into a water tank measuring 4'x 6'x 5' deep. The chlorinated water in the tank is maintained at a temperature of about 34o C by a recirculation and heat pump. The load cells are connected to a computerized scale with a digital LCD read-out that accurately measures weights to 0.001 kg. Tare weights may be canceled electronically. The participant sits in the chair, immersed to the neck, and then expires maximally while leaning forward so that the head is completely submerged. The participant maintains this position of complete immersion at maximal expiration for approximately 10 seconds while an underwater weight is recorded. Ten repeated measurements are made using this procedure, and an average of the last three are used to compute body density. Underwater weights have been measured since 1977.

Residual volume:

Residual volume is measured on land in approximately the same position as that assumed by the participant in underwater weighing. Residual volume is measured on a Gould 2100 computerized lung function analyzer. Residual volume of each participant is measured twice, and the mean value is used in the body density calculations. Residual volume has been in use since 1977.

Bioelectric impedance:

Bioelectric impedance has been collected from participants since 1986 using single-frequency RJL and Valhalla bioelectric impedance analyzers. The latter is the same impedance instrument used in NHANES III. For total body impedance, a receiving electrode is attached to the anterior surface of the right ankle midway between the malleoli of the tibia and the fibula and the other electrode is placed on the posterior surface of the right wrist midway between the distal condyles of the radius and ulna. The source electrodes are attached to the anterior surface of the foot and to the posterior surface of the hand 5.0 cm distal to the respective receiving electrodes. Bioelectric impedance has been in use since 1984.

Ultrasound:

Ultrasonic measurements of subcutaneous tissue are made at five sites: triceps, mid-thigh, suprailiac, paraspinal, and sacral using a Shimasonic SDL-32. Ultrasound transmission gel is placed upon each site and a 5 MHz transducer is used to acquire the images which are printed on a Mitsubishi video copy processor. Repeated images are made at each site, and the subcutaneous thicknesses are measured.

Total body water (TBW):

TBW is measured from deuterium oxide (D2O) dilution by nuclear magnetic resonance (NMR) spectroscopy. D2O is given to each participant (0.2 ml/kg body weight, 99.8% pure) in 150 ml distilled water. For the next two hours, participants fast and refrain from any body eliminations. At the end of 2 hours, 3.0 ml of saliva are collected. Analysis of the saliva samples utilizes NMR spectroscopy and comparison against a calibration curve. The intensity of the deuterium signal is measured, and the peak area obtained from Lorentian curve fitting. NMR analysis of D2O is conducted at the Cox Institute, Wright State University School of Medicine. Mean differences in replicate measures of TBW are about 1.0 l (SD = 0.6 l). Total body water has been measured in the Lifespan Health Research Center since 1987.

Grip strength and blood pressure:

Grip strength is measured at each examination using a Lafayette hand dynamometer. Systolic and fourth and fifth phase diastolic blood pressures are measured seated by specially trained observers in a rigorously standardized manner. Blood pressure data have been collected since the early 1930s.

Skeletal maturation:

In the longitudinal growth study many asessments made of participants are measures of maturation. Skeletal maturation involves the changes in the bones as an individual becomes an adult. This has been an area of interest in the Fels Longitudinal Study for most of the history of the study. In the 1970s the RWT (Roche-Wainer-Thissen) method was developed for assessing the skeletal maturation of the knee. It uses 28 traits, or indicators, and 10 measurements to determine skeletal age. This method can be used alone or with the FELS method for assessment of skeletal age using the hand-wrist to evaluate an individual's skeletal maturity. Knee x-rays are no longer routinely taken during growth study visits, but hand-wrist x-rays are taken on most participants between ages 8 and 18 years. The FELS method was developed in the 1980s and is based on 98 indicators and 13 measurements. At a given chronological age only 25-30% of the indicators in the RWT or FELS methods are actually used because there is a short age range in which some indicators provide useful information. Skeletal age can differ in two children of the same chronological age and stature and still be normal.

Health history, menstruation, smoking, alcohol, function, and physical activity:

Demographic information and a comprehensive health history questionnaire are collected from participants at each examination. These data are used to help describe outliers and to elucidate possible confounding interactions and associations within the data. Habitual physical activity is estimated for previous year and previous day using modified Baecke questionnaires to categorize participants by calculating a total activity score from work, sports, and non-sports leisure time activity indices.

At each examination, the participant is given a series of questionnaires to complete which include an interval medical history (a 5-page detailed inquiry of current health status including chronic, acute and infectious conditions), physical activity (a 2-page detailed inquiry relating to frequency, intensity, duration and type of exertion spent in work and leisure activities), tobacco and alcohol use (a 4-page inquiry relating to current alcohol, tobacco and drug usage or exposure), and a menstrual history (three, 2-page inquires depending upon the age of the women relating to gynecological health and status and supplemental hormone use). The tobacco and alcohol forms include questions about smokeless tobacco and exposure to environmental smoke. The SF-36 is used to assess function and well being for participants 60 years and older . The SF-36 is an accepted and validated assessment tool for measuring a comprehensive set of defined health concepts applicable to the aging process. Maturity is assessed in children by self administered questionnaires reflecting pubic hair development and genital development. Health, menstrual and behavior data have been collected in the Fels Longitudinal Study since 1929. Physical activity data have been collected since 1988.