title: Assessing the validity of surface electromyography for recording muscle activation patterns from serratus anterior.
abstract: OBJECTIVE
  No direct evidence exists to support the validity of using surface electrodes to record muscle activity from serratus anterior, an important and commonly investigated shoulder muscle. The aims of this study were to determine the validity of examining muscle activation patterns in serratus anterior using surface electromyography and to determine whether intramuscular electromyography is representative of serratus anterior muscle activity.
  
  
  METHODS
  Seven asymptomatic subjects performed dynamic and isometric shoulder flexion, extension, abduction, adduction and dynamic bench press plus tests. Surface electrodes were placed over serratus anterior and around intramuscular electrodes in serratus anterior. Load was ramped during isometric tests from 0% to 100% maximum load and dynamic tests were performed at 70% maximum load. EMG signals were normalised using five standard maximum voluntary contraction tests.
  
  
  RESULTS
  Surface electrodes significantly underestimated serratus anterior muscle activity compared with the intramuscular electrodes during dynamic flexion, dynamic abduction, isometric flexion, isometric abduction and bench press plus tests. All other test conditions showed no significant differences including the flexion normalisation test where maximum activation was recorded from both electrode types. Low correlation between signals was recorded using surface and intramuscular electrodes during concentric phases of dynamic abduction and flexion.
  
  
  CONCLUSIONS
  It is not valid to use surface electromyography to assess muscle activation levels in serratus anterior during isometric exercises where the electrodes are not placed at the angle of testing and dynamic exercises. Intramuscular electrodes are as representative of the serratus anterior muscle activity as surface electrodes.
authors.affiliation: Discipline of Exercise and Sport Science, Faculty of Health Sciences, The University of Sydney, Australia.
authors.forename: Lucien
authors.initials: L
authors.lastname: Hackett
authors.affiliation: Discipline of Biomedical Science, Sydney Medical School, The University of Sydney, Australia. Electronic address: darren.reed@sydney.edu.au.
authors.forename: Darren
authors.initials: D
authors.lastname: Reed
authors.affiliation: Discipline of Exercise and Sport Science, Faculty of Health Sciences, The University of Sydney, Australia.
authors.forename: Mark
authors.initials: M
authors.lastname: Halaki
authors.affiliation: Discipline of Biomedical Science, Sydney Medical School, The University of Sydney, Australia.
authors.forename: Karen A
authors.initials: KA
authors.lastname: Ginn
mesh_terms: D000328:Adult; D004566:Electrodes; D004576:Electromyography / Q000379:methods*; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D015203:Reproducibility of Results; D012782:Shoulder / Q000502:physiology*; D012785:Shoulder Joint / Q000502:physiology; D055815:Young Adult
keywords: Electromyography; Muscle activation; Serratus anterior; Shoulder