title: Reduced quadriceps activation after lumbar paraspinal fatiguing exercise.
abstract: BACKGROUND
  Although poor paraspinal muscle endurance has been associated with less quadriceps activation (QA) in persons with a history of low back pain, no authors have addressed the acute neuromuscular response after lumbar paraspinal fatiguing exercise.
  
  
  OBJECTIVE
  To compare QA after lumbar paraspinal fatiguing exercise in healthy individuals and those with a history of low back pain.
  
  
  METHODS
  A 2 x 4 repeated-measures, time-series design.
  
  
  METHODS
  Exercise and Sport Injury Laboratory.
  
  
  METHODS
  Sixteen volunteers participated (9 males, 7 females; 8 controls and 8 with a history of low back pain; age = 24.1 +/- 3.1 years, height = 173.4 +/- 7.1 cm, mass = 72.4 +/- 12.1 kg).
  
  
  METHODS
  Subjects performed 3 sets of isometric lumbar paraspinal fatiguing muscle contractions. Exercise sets continued until the desired shift in lumbar paraspinal electromyographic median power frequency was observed. Baseline QA was compared with QA after each exercise set.
  
  
  METHODS
  An electric burst was superimposed while subjects performed a maximal quadriceps contraction. We used the central activation ratio to calculate QA = (F(MVIC)/[F(MVIC) + F(Burst)])* 100, where F = force and MVIC = maximal voluntary isometric contractions. Quadriceps electromyographic activity was collected at the same time as QA measurements to permit calculation of median frequency during MVIC.
  
  
  RESULTS
  Average QA decreased from baseline (87.4% +/- 8.2%) after the first (84.5% +/- 10.5%), second (81.4% +/- 11.0%), and third (78.2% +/- 12.7%) fatiguing exercise sets. On average, the group with a history of low back pain showed significantly more QA than controls. No significant change in quadriceps median frequency was noted during the quadriceps MVICs.
  
  
  CONCLUSIONS
  The quadriceps muscle group was inhibited after lumbar paraspinal fatiguing exercise in the absence of quadriceps fatigue. This effect may be different for people with a history of low back pain compared with healthy controls.
authors.affiliation: University of Virginia, Department of Orthopaedic Surgery, Charlottesville, VA 22908-0159, USA. jmh3zf@virginia.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