Determination of quadriceps forces in squat and its application in contact pressure analysis of knee joint

While the quadriceps muscles of human body are quite important to the daily activities of knee joints, the determination of quadriceps forces poses significant challenges since it cannot be measured in vivo. Here, a novel approach is presented to obtain the forces in squat through the combination of motion photography, force transducers measuring, multi-rigid-body theory and finite element analysis. Firstly, the geometrical and angular data of human for squat process were obtained through the analysis of photographed pictures for human squat with camera. At the same time, force transducers were used to measure the reaction forces from feet and to determine the center of gravity for identical squat process. Next, based on the multi-rigid-body dynamics, a mathematical model for human right leg and foot was established in order to determine the quadriceps torques under different squat angles. Then, so as to determine the quadriceps forces along with varied squat angles, a simplified three-dimensional finite element model was built, including tibia, fibula, patella, patella ligament and quadriceps tendon. Finally, the contact pressure of knee joint was analyzed for the squat with the established model of knee joint involving the obtained quadriceps forces from finite element analysis. And it showed that in the 0–90 degree squat process, the peak value of contact pressure of articular cartilages and menisci is increased with the increased squat angle. This study can be referenced for further understanding of the biomechanical behaviors of knee, contact pressure effects of daily activities on knee, and is significantly instructive for sports rehabilitation.