title: Neuromuscular control of lumbar instability following static work of various loads.
abstract: Neuromuscular control of lumbar stability following exposure to prolonged static work, under low and high loads, was assessed in the in vivo feline model. Six sessions of 10 min work at 20N with 10 min between rest was compared to a group subjected to the same protocol but carrying high loads of 60N. Displacement and tension developed in the spine at the instant the multifidus muscles applied stabilizing contractions, and their amplitudes were obtained from their electromyogram (EMG). Significant (P < 0.001) laxity developed in the various viscoelastic tissues of the lumbar spine that did not recover during and up to 7 h of rest postwork. Simultaneously, there was a significant (P < 0.001) decrease in muscular activity in the 3-4 h immediately postwork under low load but only during the first hour in the high load group. After that period the musculature compensated for the laxity of the viscoelastic tissues by a significant (P < 0.001) increase in activity in the high-load group and a nonsignificant increase in the low group. It was concluded that during 1-3 h immediately poststatic work a significant decrease in the stabilizing function of viscoelastic tissues together with a significant decrease in muscular activity is present, and they render the spine unstable and exposed to high risk of injury. Performance of prolonged static work under low loads, while not harmful during the work, cannot be designated as a "no-risk" condition, as it may result in injury postwork.
authors.affiliation: Musculoskeletal Disorders Research Laboratory, Bioengineering Division, Department of Orthopedic Surgery, Health Sciences Center, Denver, Colorado 80045, USA.
authors.forename: Brook
authors.initials: B
authors.lastname: Le
authors.forename: Bradley
authors.initials: B
authors.lastname: Davidson
authors.forename: Deborah
authors.initials: D
authors.lastname: Solomonow
authors.forename: Bing He
authors.initials: BH
authors.lastname: Zhou
authors.forename: Yun
authors.initials: Y
authors.lastname: Lu
authors.forename: Vikas
authors.initials: V
authors.lastname: Patel
authors.forename: Moshe
authors.initials: M
authors.lastname: Solomonow
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D001696:Biomechanical Phenomena; D002415:Cats; D004548:Elasticity; D004576:Electromyography; D017079:Exercise Tolerance / Q000502:physiology; D008159:Lumbar Vertebrae / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D009469:Neuromuscular Junction / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology; D004856:Postural Balance / Q000502:physiology*; D014783:Viscosity; D016474:Weight-Bearing / Q000502:physiology