title: Influence of patterned electrical neuromuscular stimulation on quadriceps activation in individuals with knee joint injury.
abstract: BACKGROUND
  Neuromuscular Electrical Stimulation is a common intervention to address muscle weakness, however presents with many limitations such as fatigue, muscle damage, and patient discomfort that may influence its effectiveness. One novel form of electrical stimulation purported to improve neuromuscular re-education is Patterned Electrical Neuromuscular Stimulation (PENS), which is proposed to mimic muscle-firing patterns of healthy individuals. PENS provides patterned stimulating to the agonist muscle, antagonist muscle and then agonist muscle again in an effort to replicate firing patterns.
  
  
  OBJECTIVE
  The purpose of this study was to determine the effect of a single PENS treatment on knee extension torque and quadriceps activation in individuals with quadriceps inhibition.
  
  
  METHODS
  18 subjects (10 males and 8 females: 24.2±3.4 years, 175.3±11.8cm, 81.8±12.4kg) with a history of knee injury/pain participated in this double-blinded randomized controlled laboratory trial. Participants demonstrated quadriceps inhibition with a central activation ratio of ≤90%. Maximal voluntary isometric contraction of the quadriceps and central activation ratio were measured before and after treatment. The treatment intervention was a 15-minute patterned electrical stimulation applied to the quadriceps and hamstring muscles with a strong motor contraction or a sham group, who received an identical set up as the PENS group, but received a 1mA subsensory stimulation. A 2×2 (group × time) ANCOVA was used to determine differences in maximal voluntary isometric contraction and central activation ratio between groups. The maximal voluntary isometric contraction was selected as a covariate due to baseline differences.
  
  
  RESULTS
  There were no differences in change scores between pre- and post-intervention for maximal voluntary isometric contraction: (PENS: 0.09±0.32Nm/kg and Sham 0.15±0.18Nm/kg, p=0.713), or central activation ratio:(PENS: -1.22±6.06 and Sham: 1.48±3.7, p=0.270).
  
  
  CONCLUSIONS
  A single Patterned Electrical Neuromuscular Stimulation treatment did not alter quadriceps central activation ratio or maximal voluntary isometric contraction. Unlike other types of muscle stimulation, PENS did not result in a reduction of quadriceps torque.
  
  
  METHODS
  Level III.
authors.affiliation: Exercise and Sport Injury Laboratory, University of Virginia, Charlottesville, VA USA.
authors.forename: Neal R
authors.initials: NR
authors.lastname: Glaviano
authors.affiliation: Exercise and Sport Injury Laboratory, University of Virginia, Charlottesville, VA USA.
authors.forename: William T
authors.initials: WT
authors.lastname: Langston
authors.affiliation: Exercise and Sport Injury Laboratory, University of Virginia, Charlottesville, VA USA.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Hart
authors.affiliation: Exercise and Sport Injury Laboratory, University of Virginia, Charlottesville, VA USA.
authors.forename: Susan
authors.initials: S
authors.lastname: Saliba
keywords: Electrical stimulation; muscle inhibition; quadriceps torque