Determination of the Safe Region of Physical Activities based on a Strength Model of Trunk Muscles

F. Farahmand and M. Parnianpour (Iran)


Muscular Modeling, Trunk, Safety, Optimization.


This study aimed to determine the safe region of the physical activities in the three dimensional space of external flexion-extension, left and right lateral bending, and axial rotation (torsional) moments, considering the resulting stresses in the trunk muscles. A strength model of the trunk muscles was developed based on the static equilibrium conditions at the L3-L4 level of the lumbar spine. The matrix of muscles moment arms was obtained using the anatomical data of 10 trunk muscles. An optimization problem was formulated by which the largest external net moments were calculated provided that the resulting muscle stresses do not exceed the maximum allowable stress. This led to finding the boundary (strength) surface of the safe region in the three dimensional space of external net moments. All physical activities with resulting external net moments in the feasible region are considered to be safe, and their shortest distance from the strength surface can give an indication of the safety margin. In addition, the larger this safety margin is the longer a person may be able to maintain this task. Hence, this analysis can determine if a given task is safe and among the safe tasks which requires higher endurance. This algorithm can assist in computer aided workplace design, rehabilitation engineering and biomechanical task analysis.

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