title: Wavelet analysis of quadriceps power spectra and amplitude under varying levels of contraction intensity and velocity.
abstract: BACKGROUND
  We investigated the effect of contraction intensity [100%, 75%, 50%, and 25% maximum voluntary contraction (MVC)] and movement velocity (50°, 100°, 200°, and 400°/s) on surface electromyography root mean square amplitude (SEMGRMS ) and median frequency (SEMGMDF ) of rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM).
  
  
  METHODS
  SEMGs during knee extension were resolved into their respective frequencies using wavelet transformations.
  
  
  RESULTS
  RF, VL, and VM muscles displayed increased SEMGMDF as contraction intensity increased from 25% to 50% MVC and from 75% to 100% MVC, and each muscle displayed its own unique frequency shifting patterns. The SEMGMDF was not influenced by movement velocity. SEMGRMS increased in all 3 muscles as contraction intensity increased and was influenced by movement velocity, with the highest values observed at 400° and 200°/s.
  
  
  CONCLUSIONS
  We infer that increasing contraction intensity facilitates greater recruitment of fast-twitch muscle fibers, but there are differing responses in RF, VL, and VM muscles.
authors.affiliation: Motor Control and Biomechanics Laboratory, Department of Kinesiology, University of New Hampshire, Durham, New Hampshire, 03824, USA.
authors.forename: Ronald
authors.initials: R
authors.lastname: Croce
authors.forename: John
authors.initials: J
authors.lastname: Miller
authors.forename: Kent
authors.initials: K
authors.lastname: Chamberlin
authors.forename: David
authors.initials: D
authors.lastname: Filipovic
authors.forename: Wayne
authors.initials: W
authors.lastname: Smith
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000328:Adult; D000704:Analysis of Variance; D004576:Electromyography; D005260:Female; D006801:Humans; D007717:Knee / Q000294:innervation; D008297:Male; D008475:Median Nerve / Q000502:physiology; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology; D053581:Muscle Strength Dynamometer; D052097:Quadriceps Muscle / Q000502:physiology*; D058067:Wavelet Analysis; D055815:Young Adult
keywords: electromyography; isokinetic; power spectrum; quadriceps; wavelet transform