title: The effect of hydration status on the measurement of lean tissue mass by dual-energy X-ray absorptiometry.
abstract: OBJECTIVE
  Athletes cycle between exercise and recovery. Exercise invokes changes in total body water from thermal sweating, muscle and hepatic glycogen depletion and metabolic water loss. Recovery from exercise results in rehydration, substrate repletion, and possible glycogen supercompensation. Such changes may corrupt the measurement of hydrated tissues, such as lean tissue mass (LTM), by dual-energy X-ray absorptiometry (DXA). The purpose of this study was to determine the effect of exercise and thermal dehydration and subsequent glycogen supercompensation on DXA-based measurement of body composition.
  
  
  METHODS
  Twelve active adult (18-29 years) males exercised at 70% VO2maxon a cycle ergometer in a thermal environment (30 °C) to induce a 2.5% reduction in body mass. Participants subsequently underwent a glycogen supercompensation phase, whereby a high carbohydrate diet (8-12 g/kg body mass/day) was consumed for a 48-h period. Whole-body DXA measurement was performed at baseline, following exercise and supercompensation.
  
  
  RESULTS
  Following exercise, mean body mass decreased by -1.93 kg (95% CI -2.3, -1.5), while total LTM decreased by -1.69 kg (-2.4, -1.0). Supercompensation induced a mean body mass increase of 2.53 kg (2.0, 3.1) and a total LTM increase of 2.36 kg (1.8, 2.9). No change in total fat mass or bone mineral content was observed at any timepoint.
  
  
  CONCLUSIONS
  Training regimens that typically induce dehydration and nutrition regimens that involve carbohydrate loading can result in apparent changes to LTM measurement by DXA. Accurate measurement of LTM in athletes requires strict observation of hydration and glycogen status to prevent manipulation of results.
authors.affiliation: Sport Injury Prevention Research Centre, Faculty of Kinesiology, University of Calgary, 2500 University Drive NW, Calgary, T2N 1N4, Canada. clodagh.toomey@ucalgary.ca.|Department of Physical Education and Sport Sciences, Faculty of Education and Health Sciences, University of Limerick, Limerick, Ireland. clodagh.toomey@ucalgary.ca.
authors.forename: Clodagh M
authors.initials: CM
authors.lastname: Toomey
authors.affiliation: Department of Physical Education and Sport Sciences, Faculty of Education and Health Sciences, University of Limerick, Limerick, Ireland.
authors.forename: William G
authors.initials: WG
authors.lastname: McCormack
authors.affiliation: Department of Physical Education and Sport Sciences, Faculty of Education and Health Sciences, University of Limerick, Limerick, Ireland.
authors.forename: Phil
authors.initials: P
authors.lastname: Jakeman
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods* / Q000592:standards; D000293:Adolescent; D000328:Adult; D056352:Athletes; D001823:Body Composition; D003681:Dehydration / Q000000981:diagnostic imaging* / Q000209:etiology / Q000378:metabolism; D004040:Dietary Carbohydrates / Q000378:metabolism; D015444:Exercise; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D008297:Male; D014882:Water-Electrolyte Balance
chemical_list: D004040:Dietary Carbohydrates; D006003:Glycogen
keywords: Athletes; DXA; Glycogen; Hydration; Lean tissue mass; Measurement