The Three Classes of Anatomical Levers

Skeletal movements operate as rigid-body levers rotating around joint fulcrums. Class 1 levers (atlanto-occipital joint) position the fulcrum between effort and load. Class 2 levers (plantar flexion at metatarsals) place the load between fulcrum and effort, providing high mechanical advantage (>1.0). Class 3 levers (elbow flexion via biceps brachii) place the effort between fulcrum and load, trading mechanical advantage (<1.0) for massive distal velocity and range of motion.