The Study of Muscle and Physical Performance in African Caribbeans

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Project Summary/Abstract: Supplemental funding is requesting to purchase a preowned Hologic Horizon Dual X-ray Absorptiometry (DXA) Machine for the Tobago Health Studies (THS) Clinic. We have collected serial DXA images to measure body composition in the THS for 20 years (4 visits), and the Hologic 4500W DXA machine we have malfunctioned during the review process of the parent grant (R01AG074956) and is no longer in working order. The machine was manufactured in 2000 and has been discontinued by Hologic and the parts required to repair the machine are no longer available. The QDR 4500W is an FDA approved system and must be calibrated to factory standards and validated by a medical physicist – which is not possible. We did not budget for this in R01AG074956, as the machine was in good working order at the time of submission and during most of the review period. The primary purpose of DXA for this proposal was to measure total body and appendicular fat mass and using DXA as originally proposed has several advantages over less expensive methods of fat mass. First, switching to BIA will mean the end of the serial DXA measures that have been ongoing since 2000, and used to calculate invaluable longitudinal change data. Second, despite recent scrutiny, DXA is still considered a “gold standard” for measuring lean and fat mass and is included in just about all definitions of “sarcopenia”. For this reason, DXA has been and is being used by many studies to segment lean and fat mass. Thus, the continued use of DXA would provide the invaluable opportunity for direct comparisons with other populations. Third, DXA is more accurate than BIA for measuring fat mass and has been used to evaluate BIA's accuracy. Finally, the primary measure of total body skeletal muscle mass in this study is D3Cr, and while this method has shown to have stronger relationships with physical function in the MrOS study, these comparisons have not been made in other populations. Thus, the inclusion of DXA, as originally proposed, would significantly enhance the aims and scientific contributions of the parent R01.