title: Back extensor muscle fatigue at submaximal workloads assessed using frequency banding of the electromyographic signal.
abstract: BACKGROUND
  Changes in the mean or median frequency of the electromyographic (EMG) power spectrum are often used to assess skeletal muscle fatigue. A more global analysis of the spectral changes using frequency banding may provide a more sensitive measure of fatigue than changes in mean or median frequency. So, the aim of the present study was to characterize changes in different power spectrum frequency bands and compare these with changes in median frequency.
  
  
  METHODS
  Twenty male subjects performed isometric contractions of the back muscles in an isometric dynamometer at 30%, 40%, 50% and 60% of maximum voluntary contraction. During each contraction, surface EMG signals were recorded from the right and left longissimus thoracis muscles, and endurance time was measured. The EMG power spectra were divided into four frequency bands (20-50 Hz; 50-80 Hz; 80-110 Hz; 110-140 Hz) and changes in power in each band with fatigue were compared with changes in median frequency.
  
  
  RESULTS
  The percentage changes in 20-50 Hz band were greater than in all other and the rate of change in power, indicated by the slope, was also greatest in 20-50 Hz band. Also, 20-50 Hz band had a greater change in power than the median frequency.
  
  
  CONCLUSIONS
  Power in the low frequency part of the EMG power spectrum increases with fatigue in a load-dependent manner. The rate of change in low frequency power may be a useful indicator of fatigue rate or "fatigability" in the back muscles. Also, changes in low frequency power are more evident than changes in the median frequency.
authors.affiliation: Department of Physical Education, Biosciences Institute, São Paulo State University, Rio Claro, São Paulo, Brazil.
authors.forename: Adalgiso Coscrato
authors.initials: AC
authors.lastname: Cardozo
authors.forename: Mauro
authors.initials: M
authors.lastname: Gonçalves
authors.forename: Patricia
authors.initials: P
authors.lastname: Dolan
mesh_terms: D000328:Adult; D001416:Back Pain / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D004576:Electromyography; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D017116:Low Back Pain / Q000503:physiopathology; D008297:Male; D018763:Muscle Fatigue; D053581:Muscle Strength Dynamometer; D018482:Muscle, Skeletal / Q000503:physiopathology*; D010807:Physical Endurance; D055815:Young Adult