title: Cyclic load magnitude is a risk factor for a cumulative lower back disorder.
abstract: OBJECTIVE
  Epidemiological data suggest that high loads lifted by workers engaged in static and cyclic daily activities may be a risk factor for low back disorder. Our previous research provided physiological and biomechanical validation of the epidemiological data for static load conditions. The objective of this report was to provide physiological and biomechanical experimental validation to the epidemiological data in cyclic (repetitive) load conditions.
  
  
  METHODS
  Three groups of in vivo feline models were subjected to 3 cyclic load levels in a series of 6 periods of 10 minutes of work spaced by 10 minutes of rest followed by 7 hours of rest. Multifidus electromyography (EMG) and lumbar displacement were statistically analyzed after processing.
  
  
  RESULTS
  Delayed muscular hyperexcitability was observed only in moderate (40 N) and high (60 N) loads (P<0.0001) but was absent in low (20 N) loads. The magnitude of the delayed hyperexcitability was found to be higher (P<0.0001) in the high (60 N) loads compared with the moderate (40 N) loads.
  
  
  CONCLUSIONS
  Exposure to moderate and high loads in cyclic (repetitive) work results in an acute neuromuscular disorder indicative of soft tissue inflammation that may become chronic with further exposure.
authors.affiliation: Musculoskeletal Disorders Research Laboratory, Bioengineering Division, Department of Orthopaedics, University of Colorado Health Sciences Center, Aurora, CO 80045, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Le
authors.forename: Moshe
authors.initials: M
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
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002415:Cats; D012090:Cumulative Trauma Disorders / Q000209:etiology / Q000503:physiopathology*; D004576:Electromyography; D017116:Low Back Pain / Q000209:etiology / Q000503:physiopathology*; D008159:Lumbar Vertebrae / Q000503:physiopathology; D023421:Models, Animal; D012307:Risk Factors; D013314:Stress, Mechanical; D016474:Weight-Bearing / Q000502:physiology*