title: Variability in spine loading model performance.
abstract: OBJECTIVE
  To assess the sources of variability associated with an EMG-assisted model of spine loading.
  
  
  METHODS
  In vivo measurements of trunk dynamics, lifting moments and muscle activities were used as inputs into an EMG-assisted spine loading model.
  
  
  BACKGROUND
  Several types of variability are inherent in biomechanical assessments of risk associated with trunk bending motions during lifting. Variability may occur as a function of variations in spine loading due to either subject variations in motion profiles (kinematics) or biomechanical model performance.
  
  
  METHODS
  Twelve experienced and inexperienced materials handlers performed 10 repeated lifts where load weight, asymmetry, and velocity were varied. The experiment was replicated on a second day to assess day to day variability.
  
  
  RESULTS
  These model performance variables indicated that variability was mainly a function of subject characteristics and experience. Minor variations in variability were associated with the task asymmetry and weight lifted. Advanced analyses suggested that experienced workers had a greater range of back motion compared to inexperienced workers which would affect the length-strength component of the model calibration.
  
  
  CONCLUSIONS
  This study indicates that for the results of an EMG-assisted model to be accurate, it is important to ensure that the model reflects a realistic relationship between the trunk muscle length and the muscle force production capacity. Underestimation if this relationship can degrade model fidelity and robustness.
  
  
  CONCLUSIONS
  These results imply that by properly calibrating the model it is then reasonable to assume that the vast majority of variations observed in repeated exertions of a particular trial are due to kinematic and kinetic differences inherent in the muscle control system and not a function of model randomness.
authors.affiliation: Biodynamics Laboratory, The Ohio State University, 1971 Neil Ave, Columbus 43210, USA. wsm@osuergo.eng.ohio-state.edu
authors.forename: W S
authors.initials: WS
authors.lastname: Marras
authors.forename: K P
authors.initials: KP
authors.lastname: Granta
authors.forename: K G
authors.initials: KG
authors.lastname: Davis
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D002138:Calibration; D004576:Electromyography; D006801:Humans; D017770:Lifting; D017116:Low Back Pain / Q000503:physiopathology; D008297:Male; D013131:Spine / Q000502:physiology*; D013647:Task Performance and Analysis