As the fulcrum approaches the load, the load’s range and speed of movement decrease. When the fulcrum is equidistant between the force and load, the lever system only changes the direction of movement. The position of the fulcrum in the lever system determines the balance between speed and strength. This also explains why the thighs and upper arms are more massive than the forearms, hands, legs, and feet.Īlso, first class levers can either multiply the speed of muscle movements in exchange for decreased strength, or multiply the force of muscles in exchange for decreased speed. Less muscle in the extremities means less muscle mass to move, resulting in faster and easier movements.
This arrangement is useful in the neck and limbs, where it is advantageous to place muscles closer to the trunk or center of the body. All first class levers reverse the direction of movement like a seesaw, so that applying force in one direction results in the load moving the opposite direction. Physiologyįirst class lever systems provide a way for the body to change the direction, speed, and strength of movement at a joint. For example, the atlanto-occipital joint in the neck bears the mass of the head, while the elbow joint moves the forearm and any mass held in the hand, like a dumbbell. The load or resistance in anatomical lever systems varies by the specific case, but always refers to the mass borne or moved by the bone. The effort force is provided by muscles and is applied to the lever system at the point where the muscle’s tendon attaches to the bone serving as the lever. In the human body, a bone forms the lever and the fulcrum is a joint where a bone can move around the pivot point. Seesaws and crowbars are non-anatomical examples of first class lever systems. In a first class lever system, the fulcrum or pivot point is located on the lever between the effort force and load or resistance being moved. While less common in the body than second and third class levers, the first class lever system is found in the neck at the atlanto-occipital joint and in the elbow joint.
The first class lever is one of three classes of levers and is one possible arrangement of muscles, bones, and joints found in the human body.
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