Kinematic and kinetic analysis of knee joint during squatting

Knee function in squatting is an important consideration for activity of daily living. However, there are only a limited number of studies reporting biomechanics of deep knee flexion beyond 90⁰. The joint and muscle forces calculated from the data collected from six healthy subjects performing squatting and rising from a deep squat using a force plate, a marker system and EMG. The estimated tibio-femoral joint forces were between 4.7 and 5.6 times body weight in vertical direction and 2.9-3.5 times body weight in horizontal direction. These forces are much larger than the forces during normal walking. A mathematical model shows the external forces acting on the segments of lower limbs are the gravity forces and inertia forces due to mass segments of limb and the reactive forces transmitted from the ground. The ground reaction forces have the enormous effect on the leg during stance phase of walking whereas the gravity forces and the inertia forces are predominantly responsible for the forces at joints during swing phase of walking. The moment developed by the external forces at the respective joint is counterbalanced by the moment developed by the contraction of muscle forces about the joint to keep the joint in dynamic equilibrium.