title: Intramuscular myoelectric activity and selective coactivation of trunk muscles during lateral flexion with and without load.
abstract: METHODS
  Myoelectric activity of trunk muscles was measured intramuscularly in six healthy subjects as they maintained static trunk postures at 0 degrees, 15 degrees, and 30 degrees of lateral bending, unloaded or holding a 20-kg load in one hand alongside the body.
  
  
  OBJECTIVE
  To determine the position and load dependency of the agonistic and antagonistic myoelectric responses of deep and superficial trunk lateral flexor muscles.
  
  
  BACKGROUND
  Loading of the trunk in lateral bending is associated with incidences of low back pain. The neuromotor control of muscles surrounding the spine may be decisive for its vulnerability. Earlier documentation of the activation pattern of trunk muscles, particularly those situated deeply, is incomplete.
  
  
  METHODS
  Trunk angle was measured between S1-C7 and the vertical with a protractor. Electromyographic activity was recorded unilaterally from eight trunk muscles using intramuscular fine-wire electrodes inserted under the guidance of ultrasound.
  
  
  RESULTS
  The electromyographic data showed that all muscles on the side contralateral to the load, except rectus abdominis, had their highest activity while loaded in the position most laterally flexed to the loaded side. The degree of bilateral coactivation was greater for the ventral than for the dorsal muscles.
  
  
  CONCLUSIONS
  The myoelectric responses of most lumbar trunk muscles to static lateral flexion were dependent on trunk position and loading. The abdominal muscles demonstrated more coactivation than the other trunk muscles, and thus appeared to contribute more to trunk stabilization in laterally bent and loaded trunk positions.
authors.affiliation: Department of Neuroscience, Karolinska Institutet, and the Department of Sport and Health Sciences, University College of Physical Education and Sports, Stockholm, Sweden. qiang-min.huang@neuro.ki.se
authors.forename: Q M
authors.initials: QM
authors.lastname: Huang
authors.forename: E
authors.initials: E
authors.lastname: Andersson
authors.forename: A
authors.initials: A
authors.lastname: Thorstensson
mesh_terms: D000005:Abdomen; D000328:Adult; D001696:Biomechanical Phenomena; D004576:Electromyography; D005260:Female; D006801:Humans; D017116:Low Back Pain / Q000209:etiology*; D008161:Lumbosacral Region / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000502:physiology*; D011187:Posture; D013131:Spine / Q000033:anatomy & histology / Q000502:physiology*; D016474:Weight-Bearing