Anthropometric data can 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 measurements repeated if the initial measurement difference between the observers is greater than a preset error limit. Anthropometry has been collected continuously in the Fels Longitudinal Study since 1929.
Total and regional body composition and bone density measurements are made using a dual energy x-ray absorptiometry or DXA. The information from a total body scan includes total body bone mineral (TBBM), soft-tissue, fat and lean tissue weights, 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 percent and that of estimates of %BF for the body regions and for the whole body is less than 1.5 percent. DXA has been used in the Fels Longitudinal Study since 1990.
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.
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.
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.
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. The FELS Method for assessing the skeletal age of the hand-wrist was developed in the 1980s. Hand-wrist x-rays are taken from most participants between ages 8 and 18 years. Skeletal age can differ in two children of the same chronological age and stature and still be normal.
Demographic information and a comprehensive health history questionnaire are collected from participants at each examination. These data are used to help describe 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 five-page, detailed inquiry of current health status including chronic, acute and infectious conditions), physical activity (a two-page detailed inquiry relating to frequency, intensity, duration and type of exertion spent in work and leisure activities), tobacco and alcohol use (a four-page inquiry relating to current alcohol, tobacco and drug usage or exposure), and a menstrual history (three two-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 wellbeing 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.