title: Magnetic resonance imaging assessment of trunk muscles during prolonged bed rest.
abstract: METHODS
  Prospective longitudinal study. OBJECTIVE.: To investigate, using magnetic resonance imaging (MRI), the influence of bed rest on the lumbopelvic musculature.
  
  
  BACKGROUND
  Reduced gravitational loading and inactivity (bed rest) are known to result in significant change in musculoskeletal function, although little is known about its effects on specific muscles of the lumbopelvic region.
  
  
  METHODS
  Ten healthy male subjects underwent 8 weeks of bed rest with 6 months of follow-up. MRI of the lumbopelvic region was conducted at regular time-points during and after bed rest. Using uniplanar images at L4, cross-sectional areas (CSAs) of the multifidus, lumbar erector spinae, quadratus lumborum, psoas, anterolateral abdominal, and rectus abdominis muscles were measured.
  
  
  RESULTS
  Multifidus CSA decreased by day 14 of bed rest (F = 7.4, P = 0.04). The lumbar erector spinae and quadratus lumborum CSA showed no statistically significant difference to baseline across the time of bed rest (P > 0.05). The anterolateral abdominal, rectus abdominis, and psoas CSA all increased over this time. Psoas CSA increased by day 14 (F = 6.9, P = 0.047) and remained so until day 56, whereas the anterolateral abdominal CSA (F = 29.4, P = 0.003) and rectus abdominis CSA (F = 8.9, P = 0.03) were not statistically larger than baseline until day 56. On reambulation after completion of the bed rest phase, multifidus, anterolateral abdominal, and rectus abdominis CSA returned to baseline levels (P > 0.05) by day 4 of follow-up, whereas psoas CSA returned to baseline level after day 28 of the follow-up period.
  
  
  CONCLUSIONS
  Bed rest resulted in selective atrophy of the multifidus muscle. An increased CSA of the trunk flexor musculature (increases in psoas, anterolateral abdominal, and rectus abdominis muscles) may reflect muscle shortening or possible overactivity during bed rest. Some of the changes resemble those seen in low back pain and may in part explain the negative effects of bed rest seen in low back pain sufferers.
authors.affiliation: Division of Physiotherapy, School of Health and Rehabilitation Sciences, University of Queensland, Brisbane, Queensland, Australia. j.hides@shrs.uq.edu.au
authors.forename: Julie A
authors.initials: JA
authors.lastname: Hides
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Belavý
authors.forename: Warren
authors.initials: W
authors.lastname: Stanton
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Wilson
authors.forename: Jörn
authors.initials: J
authors.lastname: Rittweger
authors.forename: Dieter
authors.initials: D
authors.lastname: Felsenberg
authors.forename: Carolyn A
authors.initials: CA
authors.lastname: Richardson
mesh_terms: D000009:Abdominal Muscles / Q000473:pathology / Q000503:physiopathology; D000328:Adult; D001510:Bed Rest / Q000009:adverse effects*; D006801:Humans; D017116:Low Back Pain / Q000473:pathology / Q000503:physiopathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000473:pathology* / Q000503:physiopathology; D009133:Muscular Atrophy / Q000175:diagnosis* / Q000209:etiology* / Q000503:physiopathology; D016658:Psoas Muscles / Q000473:pathology / Q000503:physiopathology; D013997:Time Factors