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Arthur D. Stewart and James Hannan

Athletes have traditionally been evaluated for body composition by percent fat, percent muscle, and somatotype. Since the late 1980s, dual X-ray absorptiometry (DXA) has offered total and regional body composition of bone mineral content (BMC), lean tissue and fat, but studies involving athletes are rare (11) and have not included regional tissue distribution. In the present study, DXA was used to compare a total of 121 male subjects belonging to 9 different athletic groups and controls. ANOVA showed total tissue percent BMC, lean tissue, and fat were significantly different between the various athletic groups (p < .001). Regional differences in tissue distribution between different athletic groups affect BMC and lean tissue (p < .001), but not fat (p > .05). However, athletes of the leanest groups had different fat distribution to that of nonexercising controls (p < .01). It appears that fat distribution is nonspecific in its response to exercise, while lean and BMC distributions show highly specific adaptations to specific sports.

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Alisa Nana, Gary J. Slater, Arthur D. Stewart and Louise M. Burke

Dual energy X-ray absorptiometry (DXA) is rapidly becoming more accessible and popular as a technique to monitor body composition, especially in athletic populations. Although studies in sedentary populations have investigated the validity of DXA assessment of body composition, few studies have examined the issues of reliability in athletic populations and most studies which involve DXA measurements of body composition provide little information on their scanning protocols. This review presents a summary of the sources of error and variability in the measurement of body composition by DXA, and develops a theoretical model of best practice to standardize the conduct and analysis of a DXA scan. Components of this protocol include standardization of subject presentation (subjects rested, overnight-fasted and in minimal clothing) and positioning on the scanning bed (centrally aligned in a standard position using custom-made positioning aids) as well as manipulation of the automatic segmentation of regional areas of the scan results. Body composition assessment implemented with such protocol ensures a high level of precision, while still being practical in an athletic setting. This ensures that any small changes in body composition are confidently detected and correctly interpreted. The reporting requirements for studies involving DXA scans of body composition include details of the DXA machine and software, subject presentation and positioning protocols, and analysis protocols.