title: Effects of Volitional Spine Stabilization and Lower-Extremity Fatigue on the Knee and Ankle During Landing Performance in a Population With Recurrent Low Back Pain.
abstract: BACKGROUND
  Recurrent lower back pain (rLBP) and neuromuscular fatigue are independently thought to increase the risk of lower extremity (LE) injury. Volitional preemptive abdominal contraction (VPAC) is thought to improve lumbar spine and pelvis control in individuals with rLBP. The effects of VPAC on fatigued landing performance in individuals with rLBP are unknown.
  
  
  OBJECTIVE
  To determine the effects of VPAC and LE fatigue on landing performance in a rLBP population.
  
  
  METHODS
  Cross-sectional pretest-posttest cohort control design.
  
  
  METHODS
  A clinical biomechanics laboratory.
  
  
  METHODS
  32 rLBP (age 21.2 ± 2.7 y) but without current symptoms and 33 healthy (age 20.9 ± 2.3 y) subjects.
  
  
  METHODS
  (i) Volitional preemptive abdominal contraction using abdominal bracing and (ii) fatigue using submaximal free-weight squat protocol with 15% body weight until task failure was achieved.
  
  
  METHODS
  Knee and ankle angles, moments, electromyographic measurements from semitendinosus and vastus medialis muscles, and ground reaction force (GRF) were collected during 0.30 m drop-jump landings.
  
  
  RESULTS
  The VPAC resulted in significantly earlier muscle onsets across all muscles with and without fatigue in both groups (mean ± SD, 0.063 ± 0.016 s earlier; P ≤ .001). Fatigue significantly delayed semitendinosus muscle onsets (0.033 ± 0.024 s later; P ≤ .001), decreased GRF (P ≤ .001), and altered landing kinematics in a variety of ways. The rLBP group exhibited delayed semitendinosus and vastus medialis muscle onsets (0.031 ± 0.028 s later; P ≤ .001) and 1.8° less knee flexion at initial contact (P ≤ .008).
  
  
  CONCLUSIONS
  The VPAC decreases some of the detrimental effects of fatigue on landing biomechanics and thus may reduce LE injury risk in a rLBP population.
authors.forename: Ram
authors.initials: R
authors.lastname: Haddas
authors.forename: Steven F
authors.initials: SF
authors.lastname: Sawyer
authors.forename: Phillip S
authors.initials: PS
authors.lastname: Sizer
authors.forename: Toby
authors.initials: T
authors.lastname: Brooks
authors.forename: Ming-Chien
authors.initials: MC
authors.lastname: Chyu
authors.forename: C Roger
authors.initials: CR
authors.lastname: James
mesh_terms: D000842:Ankle / Q000502:physiology*; D001696:Biomechanical Phenomena; D003430:Cross-Sectional Studies; D004576:Electromyography; D006801:Humans; D007717:Knee / Q000502:physiology*; D017116:Low Back Pain / Q000503:physiopathology*; D009119:Muscle Contraction; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000502:physiology; D013131:Spine / Q000502:physiology*; D055815:Young Adult
keywords: ACL; ankle sprain; clinical biomechanics; hamstring strain; lower extremity injury; rehabilitation