title: Lumbar muscle activities in rapid three-dimensional pulling tasks.
abstract: METHODS
  An experimental and theoretical study in healthy young adults.
  
  
  OBJECTIVE
  To utilize myoelectric signals to investigate muscle recruitment and estimate spine loads during rapid, three-dimensional pulling tasks.
  
  
  BACKGROUND
  Most previous research concerning lumbar trunk loads has focused on quasi-static exertions and sagittally symmetric dynamic tasks.
  
  
  METHODS
  Nine young males performed dynamic pulls in five prescribed directions, requiring the active development of combined sagittal, frontal, and/or transverse moments by the lumbar muscles. Myoelectric activities were recorded from 14 lumbar muscles. Individual muscle activities were compared with their biomechanical capability to equilibrate the external moments at the L3-4 lumbar cross-section. Myoelectric signal-to-force models were used to estimate the peak loads on the lumbar spine.
  
  
  RESULTS
  The largest muscle activities always occurred in those muscles having the greatest spatial effectiveness to develop the task moments. However, abdominal oblique and latissimus dorsi muscles were at times active during pulling tasks involving substantial lateral and/or axial moments despite poor spatial effectiveness to equilibrate the task moments. Of ergonomic significance is the finding that the estimated spine compression was substantially greater when asymmetric pulls imposed twisting loads about the spine compared to equivalent symmetric pulls, reflecting the additional muscle activities required to equilibrate the twisting moments.
  
  
  CONCLUSIONS
  Asymmetric pulls resulted in some activities in obliquely oriented muscles not primarily associated with equilibrating the task moments at a single level of the lumbar trunk. Therefore, other factors, such as equilibrium requirements at other lumbar levels and trunk stiffness, may be important determinants of lumbar muscle activities during three-dimensional loadings of the trunk.
authors.affiliation: Department of Mechanical Engineering and Applied Mechanics, University of Michigan, USA.
authors.forename: D G
authors.initials: DG
authors.lastname: Thelen
authors.forename: J A
authors.initials: JA
authors.lastname: Ashton-Miller
authors.forename: A B
authors.initials: AB
authors.lastname: Schultz
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D004576:Electromyography / Q000379:methods; D006801:Humans; D008161:Lumbosacral Region / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D009068:Movement; D018482:Muscle, Skeletal / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D011446:Prospective Studies; D012016:Reference Values; D013314:Stress, Mechanical; D013997:Time Factors; D016474:Weight-Bearing / Q000502:physiology