E4 Joints Levers

Title

The joints act as levers that modify the relationship between muscle force and the resulting force on the external object. In biomechanics they are classified as first, second or third class levers depending on the relative position of the fulcrum (joint), input force (muscle) and resistance (external load). Most joints in the human body are third-class levers (muscle inserted near the fulcrum), which sacrifices mechanical advantage in exchange for greater speed and range of motion at the distal end. The mechanical advantage (MA) is the ratio between the muscle force arm d_m and the resistance arm d_r. The torque (moment) in the joint determines the demand on the articular cartilage and periarticular tissue. In joints such as the knee, the joint compression force can exceed 10 times the body weight in jumping landing. Hyaline cartilage is modeled as a biphasic material (solid phase + interstitial fluid); The effective stiffness increases with the loading speed due to the hydrostatic pressure of the fluid (poroelastic effect).

ID:457