Every morning I feed my cat, Albus. He won't leave me alone until I get out of bed and bend down to grab his food bowl! When I bend down, my knees and hips are flexing and my ankles are using dorsi-flexion. When I stand up, my knees and hips are extending, and my ankles are using plantar-flexion. All of these motions of flexion and extension of the knees, hips, and ankles are in the sagittal plane and the frontal axis. The osteokinematics of the knees flexing and extending are part of a closed kinematic chain. The arthrokinematics of the knees move in a roll and gliding motion in opposite directions because the femur is a convex bone and the unla is a concave bone. During knee flexion, the femur rolls posteriorly and glides anteriorly. During knee extension, the femur rolls anteriorly and glides posteriorly. The prime movers of knee extension are the quadriceps, which perform concentric contraction and the prime movers of knee flexion are the hamstrings, which perform eccentric contraction.
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