title: Strategies that improve paralyzed human quadriceps femoris muscle performance during repetitive, nonisometric contractions.
abstract: OBJECTIVE
  To determine the effect of combining different stimulation frequencies on the ability of paralyzed human quadriceps muscle to produce a 50 degrees knee excursion repetitively when starting at 90 degrees of flexion.
  
  
  METHODS
  Repeated-measures design.
  
  
  METHODS
  Clinical research laboratory.
  
  
  METHODS
  Complete data were collected from 9 subjects aged 11 to 25 years (mean +/- standard deviation, 17.1+/-4.5y) with spinal cord injury (SCI).
  
  
  METHODS
  Three protocols were each tested during separate sessions: 20-Hz trains of pulses followed by 66-Hz trains (C20+66), 33-Hz trains followed by 66-Hz trains (C33+66), and 66-Hz trains alone (C66). For each frequency, stimulation was repeated until the knee failed to produce a 50 degrees excursion. This approach allowed us to evaluate the response to stimulation with 20-, 33-, and 66-Hz and combinations of 20- and 66-Hz and 33- and 66-Hz trains.
  
  
  METHODS
  Number of successful contractions.
  
  
  RESULTS
  The C20 and C33 did not differ (mean, 41.0+/-12.6 excursions and 42.0+/-12.3 excursions, respectively), and each produced more excursions than the C66 protocol. The C20+66 and C33+66 protocols produced 51.4+/-15.0 and 44.9+/-13.6 excursions, respectively, and the C20+66 was the best protocol overall (all P<or=.05).
  
  
  CONCLUSIONS
  This study showed that stimulation strategies that start with low frequencies and switch to higher frequencies as the muscle fatigues could improve the ability of functional electric stimulation applications to perform repetitive, nonisometric contractions in subjects with SCI.
authors.affiliation: Graduate Program in Biomechanics, University of Delaware, Newark, DE 19716, USA.
authors.forename: Maikutlo B
authors.initials: MB
authors.lastname: Kebaetse
authors.forename: Samuel C
authors.initials: SC
authors.lastname: Lee
authors.forename: Therese E
authors.initials: TE
authors.lastname: Johnston
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Binder-Macleod
mesh_terms: D000328:Adult; D002574:Cervical Vertebrae; D002648:Child; D004558:Electric Stimulation / Q000379:methods*; D005260:Female; D006801:Humans; D007551:Isotonic Contraction / Q000502:physiology*; D007717:Knee / Q000503:physiopathology; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology; D010243:Paralysis / Q000209:etiology / Q000503:physiopathology*; D052097:Quadriceps Muscle / Q000503:physiopathology*; D013119:Spinal Cord Injuries / Q000150:complications / Q000503:physiopathology*; D013904:Thoracic Vertebrae