title: Muscle X-ray attenuation is not decreased during experimental bed rest.
abstract: BACKGROUND
  Muscle X-ray attenuation (MXA) in Hounsfield units (HU) is decreased in dystrophy, aging, and immobilization. We hypothesized a decrease also during bed rest (BR).
  
  
  METHODS
  Twenty-five healthy men performed BR for 90 days, 8 of whom performed flywheel exercise 2-3 times per week. Muscle cross-sectional area (CSA) and MXA were assessed by computed tomography.
  
  
  RESULTS
  In the control group, calf muscle CSA decreased during 89-day BR by 26.6 (SD 3.8) %, while MXA increased by 1.2 HU on day 28 and almost reached baseline values on day 89. Changes were mitigated in the flywheel group for the calf (P < 0.001). All changes were reversed within 90 days after BR.
  
  
  CONCLUSIONS
  Results contradict the initial hypothesis. Increased intramuscular blood content, interstitial fluid space shrinkage, and reduction of intramuscular lipid stores are possible explanations for the moderate increase in MXA during the initial phase of bed rest.
authors.affiliation: Institute of Aerospace Medicine, German Aerospace Center, Cologne, Germany. joern.rittweger@dlr.de
authors.forename: Jörn
authors.initials: J
authors.lastname: Rittweger
authors.forename: Klaus
authors.initials: K
authors.lastname: Möller
authors.forename: Marie-Pierre
authors.initials: MP
authors.lastname: Bareille
authors.forename: Dieter
authors.initials: D
authors.lastname: Felsenberg
authors.forename: Jochen
authors.initials: J
authors.lastname: Zange
mesh_terms: D000328:Adult; D001510:Bed Rest; D015444:Exercise / Q000502:physiology; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging* / Q000503:physiopathology; D009133:Muscular Atrophy / Q000000981:diagnostic imaging* / Q000503:physiopathology; D011859:Radiography