W S Marras1, K P Granta, K G Davis. 1. Biodynamics Laboratory, The Ohio State University, 1971 Neil Ave, Columbus 43210, USA. wsm@osuergo.eng.ohio-state.edu
Abstract
OBJECTIVE: To assess the sources of variability associated with an EMG-assisted model of spine loading. DESIGN: 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. RELEVANCE: 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.
RCT Entities:
OBJECTIVE: To assess the sources of variability associated with an EMG-assisted model of spine loading. DESIGN: 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. RELEVANCE: 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.