biomechanics of doing a squat

Each night before I go to bed, I attempt to do 20 squats. Doing a squat is an example of osteokinematics of a closed-kinematic chain because my feet are remaining stationary while my quadriceps are doing the work. When I start doing a squat, I place my feet hip distance apart and extend my arms directly in front of me. Next, I bend down to where my knees are parallel to my hips and repeat these steps. My legs begin in a flexed position when my legs are hip distance apart and when I squat my knees forward parallel to my hips. My legs then become extended when rising back up to a standing position to finish the squat cycle (backwards motion). The gluteus maximus is responsible for hip extension and the quadriceps are responsible for knee extension.  The movements of flexion and extension occur at the hip, knee and ankle joints in the sagittal plane about a frontal axis. As for arthrokinematics, the moving femur rolls anteriorly and glides posteriorly on the tibial plateau. The moving femur is the concave segment and the tibial plateau is the convex segment. Also, the hip joint is the convex segment and the femur is the concave segment. The hip is a ball and socket joint because the hip glides in a posterior direction. Dorsiflexion is another important movement in the ankle joint to perform a proper squat. Dorsiflexion occurs when the top of the foot is brought closer to the shin. The primary movers of a squat are the quadriceps and the gluteus maximus which forms a concentric contraction. However, the eccentric contraction occurs during the downward phase of the squat when I am lowering my body. The concentric contraction occurs during the lifting part of the phase when I rise to stand up.