Effects of exercise sessions on DXA measurements of body composition in active people.
OBJECTIVE
Dual-energy x-ray absorptiometry (DXA) is rapidly becoming more accessible and popular as a technique to monitor body composition, especially in athletic populations. This study investigates the reliability of DXA in measuring body composition of active individuals, specifically to ascertain biological variability associated with two different types of exercise under free-living conditions in active individuals.


METHODS
Well-trained individuals (27 strength-trained male subjects, 14 female cyclists, and 14 male cyclists) underwent three whole-body DXA scans over a 1-d period: in the morning after an overnight fast, approximately 5 min later after repositioning on the scanning bed, and shortly after a self-chosen exercise session (resistance training or cycling). Subjects were allowed to consume food and fluid ad libitum before and during exercise as per their usual practices. Magnitude of typical (standard) errors of measurement and changes in the mean of DXA measures were assessed by standardization.


RESULTS
Exercise and its related practices of fluid and food intake are associated with changes in the mean estimates of total and regional body composition that range from trivial to small but substantial. An exercise session also increases the typical error of measurement of these characteristics by approximately 10%.


CONCLUSIONS
The easiest and most practical way to minimize the biological "noise" associated with undertaking a DXA scan is to have subjects fasted and rested before measurement. Until sufficient data on the smallest important effect are available, both biological and technical "noises" should be minimized so that any small but potentially "real" changes can be confidently detected.
AIS Sports Nutrition, Australian Institute of Sport, Canberra, ACT, Australia. alisa.nana@ausport.gov.au
Alisa
A
Nana
Gary J
GJ
Slater
Will G
WG
Hopkins
Louise M
LM
Burke
D015502:Absorptiometry, Photon / Q000592:standards; D050154:Adiposity / Q000502:physiology; D000328:Adult; D056352:Athletes; D001642:Bicycling / Q000502:physiology*; D001823:Body Composition / Q000502:physiology*; D015519:Bone Density / Q000502:physiology; D004326:Drinking / Q000502:physiology; D004435:Eating / Q000502:physiology; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D015203:Reproducibility of Results; D055070:Resistance Training; D012737:Sex Factors