title: Differential activation of the thoracic multifidus and longissimus thoracis during trunk rotation.
abstract: METHODS
  Cross-sectional study.
  
  
  OBJECTIVE
  To develop a technique to measure electromyographic (EMG) activity of deep and superficial paraspinal muscles at different thoracic levels and to investigate activity of these muscles during seated trunk rotation.
  
  
  BACKGROUND
  Few studies have compared activity of deep and superficial paraspinal muscles of the thorax during trunk rotation, and conflicting results have been presented. Conflicting data may result from recording techniques or variation in activity between thoracic regions.
  
  
  METHODS
  EMG recordings were made from deep (multifidus/rotatores) and superficial (longissimus) paraspinal muscles at T5, T8, and T11 using selective intramuscular electrodes. Ten subjects rotated the trunk to end of range in each direction. EMG amplitude was measured in neutral, at end of range, and during four epochs, which represented four quarters of the movement.
  
  
  RESULTS
  During trunk rotation in sitting, longissimus EMG either increased with ipsilateral rotation (T5) or decreased with contralateral rotation (T5, T8, T11). In contrast, multifidus EMG was more variable and was either active with rotation in both directions (particularly T5) or with one movement direction.
  
  
  CONCLUSIONS
  The deep and superficial muscles of the thorax are differentially active, and the patterns of activity differ between the regions of the thorax. Data from this study support the hypothesis that multifidus may have a role in control of segmental motion at T5. Variability in multifidus activity at T8 and T11 suggests that this muscle may also control coupling between rotation and lateral flexion.
authors.affiliation: Division of Physiotherapy, University of Queensland, Brisbane, Queensland, Australia.
authors.forename: Linda-Joy
authors.initials: LJ
authors.lastname: Lee
authors.forename: Michel W
authors.initials: MW
authors.lastname: Coppieters
authors.forename: Paul W
authors.initials: PW
authors.lastname: Hodges
mesh_terms: D000328:Adult; D003430:Cross-Sectional Studies; D004567:Electrodes, Implanted; D004576:Electromyography / Q000295:instrumentation / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000502:physiology*; D011187:Posture; D012399:Rotation; D013904:Thoracic Vertebrae; D014463:Ultrasonography