While the quadriceps muscles of human body are quite important to the daily ac-tivities 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 cam-era.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 un-derstanding of the biomechanical behaviors of knee,contact pressure effects of daily activities on knee,and is significantly instructive for sports rehabilitation.
In the present paper, the ground reaction force （GRF） acting on foot in slow squat was determined through a force measuring system, and at the same time, the kinematic data of human squat were obtained by analyzing the photographed image sequences. According to the height and body weight, six healthy volunteers were selected, three men in one group and the other three women in another group, and the fundamental parameters of subjects were recorded, including body weight, height and age, etc. Based on the anatomy characteristics, some markers were placed on the right side of joints. While the subject squatted at slow speed on the force platform, the ground reaction forces on the forefoot and heel for each foot were obtained through calibrated force platform. The analysis results show that the reaction force on heel is greater than that on forefoot, and double feet have nearly constant force. Moreover, from processing and analyzing the synchronously photographed image sequences in squat, the kinematic data of human squat were acquired, including mainly the curves of angle, angular velocity and angular acceleration varied with time for knee, hip and ankle joints in a sagittal plane. The obtained results can offer instructive reference for photographing and analyzing the movements of human bodies, diagnosing some diseases, and establishing in the future appropriate mathematical models for the human motion.
