title: Comparison of torque and discomfort produced by sinusoidal and rectangular alternating current electrical stimulation in the quadriceps muscle at variable burst duty cycles.
abstract: OBJECTIVE
  The aim of this study was to investigate the effect of neuromuscular electrical stimulation burst duty cycle (BDC) and current type (sinusoidal alternating current [sAC] vs. rectangular alternating current [rAC]) on the electrically induced isometric torque (EIT) and discomfort. Pulsed current (PC) stimulation, which corresponds to one pulse rAC, was included in testing.
  
  
  METHODS
  A repeated-measures design was used. The left quadriceps of 22 healthy subjects (mean ± SD age, 33 ± 8 yrs) were stimulated alternately with sAC and rAC current bursts (4-kHz carrier frequency; 71 bursts per second burst frequency) to produce isometric contractions. A range of BDCs were tested for sAC (7%-50%) and rAC (2%-18%) stimulation at fixed intensities while EIT and discomfort were recorded. BDC presentation order was randomized.
  
  
  RESULTS
  Overall, both current types elicited peak EIT at ∼14% BDC (range, 7%-21%). Significantly more EIT was produced by rAC than by sAC stimulation (P < 0.005). Discomfort increased with BDC and was similar for both current types.
  
  
  CONCLUSIONS
  The study confirmed previous findings that conventional sAC stimulation (50% BDC) and pulsed current stimulation (rAC with 2% BDC) used in sports and rehabilitation produce similar EIT levels. However, rAC stimulation at low BDC (7%-18%) was more effective (+35% torque produced with similar discomfort) than pulsed current or conventional sAC.
authors: From the Center for Sensorimotor Research, Department of Neurology, Ludwig-Maximilians University, Munich, Germany (JS); and Discipline of Exercise and Sports Science, Faculty of Health Sciences, University of Sydney, Sydney, Australia (CF).
authors: Johann
authors: J
authors: Szecsi
authors: Che
authors: C
authors: Fornusek
mesh_terms: D000328:Adult; D004599:Electric Stimulation Therapy / Q000009:adverse effects* / Q000379:methods*; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007719:Knee Joint / Q000502:physiology; D008297:Male; D053580:Muscle Strength / Q000502:physiology*; D010146:Pain / Q000209:etiology*; D052097:Quadriceps Muscle / Q000502:physiology*; D013997:Time Factors; D019415:Torque