title: Quadriceps inhibition after repetitive lumbar extension exercise in persons with a history of low back pain.
abstract: BACKGROUND
  A neuromuscular relationship exists between the lumbar extensor and quadriceps muscles during fatiguing exercise. However, this relationship may be different for persons with low back pain (LBP).
  
  
  OBJECTIVE
  To compare quadriceps inhibition after isometric, fatiguing lumbar extension exercise between persons with a history of LBP and control subjects.
  
  
  METHODS
  A 2 x 3 factorial, repeated-measures, time-series design with independent variables of group (persons with a history of LBP, controls) and time (baseline, postexercise set 1, postexercise set 2).
  
  
  METHODS
  University research laboratory.
  
  
  METHODS
  Twenty-five subjects with a history of LBP were matched by sex, height, and mass to 25 healthy control subjects.
  
  
  METHODS
  Electromyography median frequency indexed lumbar paraspinal muscular fatigue while subjects performed 2 sets of isometric lumbar extension exercise. Subjects exercised until a 15% downward shift in median frequency for the first set and a 25% shift for the second set were demonstrated.
  
  
  METHODS
  Knee extension force was measured while subjects performed an isometric maximal quadriceps contraction. During this maximal effort, a percutaneous electric stimulus was applied to the quadriceps, causing a transient, supramaximal increase in force output. We used the ratio between the 2 forces to estimate quadriceps inhibition. Quadriceps electromyographic activity was recorded during the maximal contractions to compare median frequencies over time.
  
  
  RESULTS
  Both groups exhibited significantly increased quadriceps inhibition after the first (12.6% +/- 10.0%, P < .001) and second (15.2% +/- 9.7%, P < .001) exercise sets compared with baseline (9.6% +/- 9.3%). However, quadriceps inhibition was not different between groups.
  
  
  CONCLUSIONS
  Persons with a history of LBP do not appear to be any more or less vulnerable to quadriceps inhibition after fatiguing lumbar extension exercise.
authors.affiliation: University of Virginia, Department of Orthopaedic Surgery,Charlottesville, VA, USA. jmh3zf@verginia.edu
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Hart
authors.forename: Julie M
authors.initials: JM
authors.lastname: Fritz
authors.forename: D Casey
authors.initials: DC
authors.lastname: Kerrigan
authors.forename: Ethan N
authors.initials: EN
authors.lastname: Saliba
authors.forename: Bruce M
authors.initials: BM
authors.lastname: Gansneder
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Ingersoll