Lever Systems in the Human Body PDF

Lever Systems in the Human Body Focus Question How do the three classes of levers in the human body function to produce movement?  Levers are simple machines. A machine is a device, consisting of fixed yet interrel...

Lever Systems in the Human Body Focus Question How do the three classes of levers in the human body function to produce movement?  Levers are simple machines. A machine is a device, consisting of fixed yet interrelated parts, that is capable of altering the direction and magnitude of a force. Levers perform one or more of the following functions: - Balance two or more forces, - Provide a force advantage, whereby less effort force is required to overcome a greater resistance force or, - Provide an advantage in speed of movement, What are Levers? whereby the load to be moved moves farther and faster than the effort force. Levers in the Human Body The machine-like configurations of the bone- joint-muscle arrangements in our bodies are essentially levers. Knowledge of these arrangements can form the basis for developing musculoskeletal training and conditioning programs, as well as rehabilitative exercise regimens. Knowledge of these arrangements can also be used to re-design the physical world in which we live and work in order to make our movements safer and more efficient. Classifying Levers There are three classes of levers. These classes of levers are defined according to the relative positioning of the following components: - The fulcrum or joint (the axis of rotation). The joint where the bones come together is the axis or “fulcrum” - The effort (point of application of the force). The force applied through the muscle contraction (the pull on the moveable bone at the attachment site) is the “effort” - The load (the mass of the object, body, or part being moved; also known as the resistance). The mass to be moved by the muscle is the “load.” Classifying Levers The Class 1 Lever A Class 1 lever is one in which the fulcrum (the axis of rotation) is located between the point of application of the force (the effort) and the resistance (the load) being moved. Everyday examples of first class levers include: - See-saws - Crowbars - Pliers - Scissors (two first-class levers joined together) - A hammer pulling out a nail A Class 1 Lever in the Human Body An example of a Class 1 lever in the human body is the neck as it shifts from a position of flexion to a position of extension. The contraction of the trapezius muscle (effort) permits extension of the head (resistance). The spine is the fulcrum upon which the neck muscles lift the head. A Class 1 Lever is the most versatile of all levers. It can afford a speed and/or force advantage. The Class 2 Lever A Class 2 lever is one in which the resistance, (the load) is positioned between the point of application of the force (the effort) and the axis of rotation (the fulcrum) Everyday examples of second class levers include: - Wheelbarrows - Staplers - Doors - Can Openers  A Class 2 Lever in the Human Body An example of a Class 2 lever in the human body occurs when standing on one’s toes (plantar flexion) This lever mechanism is capable of moving almost the entire weight of an individual (load) during plantar flexion (standing on one’s toes), by having the fulcrum being the metatarsophalangeal joint and the force coming from the pull of the gastrocnemius muscle. A Class 2 lever affords a force advantage: a relatively small effort can lift a large load. A Class 3 Lever A Class 3 lever is one in which the point of application of the force (the effort) is located between the fulcrum (the axis of rotation) the resistance (the load). Everyday examples of third class levers include: - Brooms - Rakes - Fishing rods - Baseball bats  A Class 3 Lever in the Human Body An example of a Class 3 lever in the human body is a person performing a biceps curl. The biceps muscle (effort) inserts on the radius (at the end of which is the load itself) in combination with the elbow joint (fulcrum). This is the most common type of lever found within the human body A Class 3 lever provides a speed advantage, allowing relatively light resistance loads to be moved through a greater ranger of motion.  To understand levers you must have an understanding of where the muscle (force) inserts. Although the bicep brachii muscle sits on the humerus, it inserts on the radius and therefore, the force is applied to the radius, not the humerus. This results in the lever organization being: Fulcrum (elbow joint), Effort (bicep brachii), Load (weight in hand) & therefore a 3rd class lever. The “ARF” of Levers A – axis/joint R – resistance/weight F – force/muscle Center of lever/pivot point What the lever system is Primary driving force behind the In people – the joint Attempting to move, cut, break or lever system lift This is what makes the lever go into Counterbalanced by the F (force) action and counterbalances the R (resistance) In people and exercise we would regard the resistance as the In people the force will be the weights muscle contracting How do you tell the difference between Class 1, 2, 3? Remember “ARF” If A is in the middle – Class 1 lever If R is in the middle – Class 2 lever If F is in the middle – Class 3 lever  Pg 180-181 in workbook Watch the following video: Homework https://drive.google.com/file/d/0B7KZLDoNKgr CNEtpUGJjMGs1ZWs/view