title: Impact of Varying the Parameters of Stimulation of 2 Commonly Used Waveforms on Muscle Force Production and Fatigue.
abstract: METHODS
  Laboratory-based experimental study using a repeated-measures design.
  
  
  OBJECTIVE
  To determine the effect of varying stimulation parameters of burst-modulated alternating current (BMAC) and pulsed current (PC) on quadriceps femoris muscle force output and fatigue.
  
  
  BACKGROUND
  The impact of altering stimulation parameters on muscle force and fatigue using PC has been well described; however, less is known regarding BMAC.
  
  
  METHODS
  Quadriceps femoris muscle force was measured during a series of neuromuscular electrical stimulation-induced muscle contractions, with varying combinations of pulse duration and frequency, using PC or varying duty cycles and burst frequencies using BMAC. Additionally, muscle fatigue tests were conducted bilaterally with different stimulation waveforms and parameters.
  
  
  RESULTS
  For PC, the product of pulse duration and frequency was strongly predictive of muscle force output (R(2) = 0.85, P<.05). When using BMAC, the duty cycle was a strong predictor of force output (R(2) = 0.91, P<.05). Altering the frequency during BMAC had no effect on muscle force production, as opposed to the classic force-frequency relationship consistently observed with PC. Waveform type significantly impacts muscle fatigue, the BMAC resulted in a more rapid rate of fatigue irrespective of stimulation frequency, and it was confirmed again that lower frequencies of PC result in less fatigue during repeated muscle contractions.
  
  
  CONCLUSIONS
  In this study, altering the burst frequency of BMAC did not influence muscle force or fatigue, whereas the duty cycle significantly impacted muscle force production. Frequency of PC impacted both force and fatigue as expected, demonstrating increased muscle force and fatigue with increased frequency.
authors.affiliation: Department of Physical Therapy, University of Alabama at Birmingham, Birmingham, AL.
authors.forename: Donald H
authors.initials: DH
authors.lastname: Lein
authors.forename: Christina
authors.initials: C
authors.lastname: Myers
authors.forename: C Scott
authors.initials: CS
authors.lastname: Bickel
mesh_terms: D000328:Adult; D004558:Electric Stimulation / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D052097:Quadriceps Muscle / Q000502:physiology
keywords: burst-modulated alternating current; electrotherapy; pulsed current