Calculation of muscle forces during normal gait under consideration of femoral bending moments

• We examine femoral stress calculations for clinical usage.
• We introduce a new approach for improved calculation of muscle forces.
• The new approach will not overload bones by bending forces.
• We demonstrate the functioning by usage of comprehensive subject specific data.
• We validate results with clinical in vivo data.

This paper introduces a new approach for computing lower extremity muscle forces by incorporating equations that consider “bone structure” and “prevention of bending by load reduction” into existing optimization algorithms.Lower extremity muscle and joint forces, during normal gait, were calculated and compared using two different optimization approaches. We added constraint equations that prevent femoral bending loads to an existing approach that considers “minimal total muscular force”. Gait parameters such as kinematics, ground reaction forces, and surface electromyographic activation patterns were examined using standardized gait analysis. A subject-specific anatomic model of the lower extremities, obtained from magnetic resonance images of a healthy male, was used for the simulations. Finite element analysis was used to calculate femoral loads.The conventional method of calculating muscle forces leads to higher rates of femoral bending and structural stress than the new approach. Adding equations with structural subject-specific parameters in our new approach resulted in reduced femoral stress patterns.These findings show that our new approach improves the accuracy of femoral stress and strain simulations. Structural overloads caused by bending can be avoided during inverse calculation of muscle forces.