title: Electromyographic amplitude and frequency changes in the iliocostalis lumborum and multifidus muscles during a trunk holding test.
abstract: OBJECTIVE
  Muscle endurance is an important variable to measure in the assessment of back muscle function. This study investigated the electromyographic (EMG) activity and fatigue patterns of iliocostalis lumborum and multifidus muscles during a trunk holding test.
  
  
  METHODS
  Sixteen male subjects (mean age = 24.2 years, SD = 4.2, range = 20.6-31.9) without low back pain or known pathology were recruited in the study.
  
  
  METHODS
  Surface EMG electrodes were used to record the activity of iliocostalis lumborum and mutifidus muscles during a 60-second isometric contraction. To reflect the activity level and fatigue rate of the muscles. EMG amplitude (root mean square [RMS] values) and a frequency variable (median frequency [MF]) were measured.
  
  
  RESULTS
  The multifidus muscle displayed a higher level of activity, initial MF, and normalized MF slope than did the iliocostalis lumborum muscle. There was no difference, however, in the normalized RMS slope between the two muscles. The correlations between the normalized MF slope and the RMS slope of the two muscles were nonsignificant.
  
  
  CONCLUSIONS
  This study shows that monitoring frequency changes of the EMG signals may enable therapists to quantify the fatigue changes of individual muscles during the trunk holding test. The higher fatigue rate shown in the multifidus muscle compared with the iliocostalis lumborum muscle may be due to the higher activity level of the multifidus muscle during te trunk holding contraction. This greater activity of the multifidus muscle during the contraction might be explained by the functional differences between these two muscles.
authors.affiliation: Department of Rehabilitation Sciences, Hong Kong Polytechnic University, Hung Hom, Hong Kong.
authors.forename: J K
authors.initials: JK
authors.lastname: Ng
authors.forename: C A
authors.initials: CA
authors.lastname: Richardson
authors.forename: G A
authors.initials: GA
authors.lastname: Jull
mesh_terms: D000328:Adult; D001415:Back / Q000502:physiology*; D004576:Electromyography / Q000379:methods*; D005583:Fourier Analysis; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D016018:Least-Squares Analysis; D008297:Male; D008432:Mathematical Computing; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*