title: Reliability of surface electromyographic measurements.
abstract: OBJECTIVE
  The aim of the study was to investigate short-term, intermediate-term and long-term reliability of surface electromyographic (EMG) measurements.
  
  
  METHODS
  Eighteen healthy subjects performed 810 isometric knee extension tests. Reliability for maximum voluntary contraction (MVC) and 50% MVC was assessed with retest intervals of 3 min, 90 min and 6 weeks. Reliability for sustained contractions was assessed with retest intervals of 90 min and 6 weeks. EMG was recorded from the rectus femoris, vastus lateralis and vastus medialis muscles. The root mean square (RMS) and the median frequency (MF) parameters were extracted. At sustained contraction tasks, estimated linear regression values of both parameters were analyzed. Bland-Altman-plots, coefficient of repeatability, Pearson's coefficient of correlation and intra class correlation (ICC) procedures were applied to assess test-retest reliability.
  
  
  RESULTS
  EMG recordings taken at short-term intervals were generally better reproducible than those of the longer-term intervals. Moreover, 50% MVC EMG recordings demonstrated better reproducibility than 100% MVC measurements, and EMG recorded from the rectus femoris were more constant than that from the vastus lateralis or vastus medialis. The MF parameter recorded from the rectus femoris was the only reliable parameter of EMG fatigue change.
  
  
  CONCLUSIONS
  In our set up, EMG measurement is best suited for clinical applications if submaximal MVC measurements are performed and signal is taken from rectus femoris muscle.
authors.affiliation: Department of Physical Medicine and Rehabilitation, University of Vienna, Austria. kollmitz@bu.edu
authors.forename: J
authors.initials: J
authors.lastname: Kollmitzer
authors.forename: G R
authors.initials: GR
authors.lastname: Ebenbichler
authors.forename: A
authors.initials: A
authors.lastname: Kopf
mesh_terms: D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology; D009132:Muscles / Q000502:physiology*; D015203:Reproducibility of Results; D013997:Time Factors