The majority of movements in the human body are classified as Third-Class Lever systems. In a Third-Class Lever system, the effort is the middle component and lies between the fulcrum and load. There are many examples of Third Class Lever systems, including both flexion and extension at the knee joint. During a biceps curl, the fulcrum is the elbow joint, the effort comes from the biceps contracting and the resistance is the weight of the forearm and any weight that it may be holding.
