1. LEVERS
~ Archimedes

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What Are Levers?
Levers are simple machines. A machine 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, whereby the load to be moved moves farther and faster than the effort force.
© 2015 Thompson Educational Publishing, Inc.

3. Levers in the Human Body
The machine-like configurations of the bone- joint-muscle arrangements in our bodies are essentially levers.
for developing musculoskeletal training and conditioning programs, as well as rehabilitative exercise regimens.
used to re-design the physical world in which we live and work in order to make our movements safer and more efficient.
© 2015 Thompson Educational Publishing, Inc.

4. Anatomy of The Lever
fulcrum

5. Anatomy of the lever
Input Force – Force exerted ON the lever (the effort-point of application of the force)
Output Force – Force exerted BY the lever
(the load-mass of object, body, or part being moved; also known as resistance)
The Lever is a simple machine. A simple machine is a device that has an input and output force. The Fulcrum is the point around which the lever rotates, and is pretty much synonymous with levers. It was Aristotle that said “ Give me a lever and a fulcrum and I shall move the Earth.” The lever pictured is only one kind of lever. There are a total of 3 “classes” of levers. This one is of class One, because the fulcrum is in between the input and output forces. We find examples of all three classes of levers everywhere.

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Classifying Levers
There are three classes of levers. These classes of levers are defined according to the relative positioning of the following components:
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7. First Class Levers – “See-Saw” Levers
The fulcrum is located between the effort arm and the resistance arm.
First class levers can multiply force and distance.

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A Class 1 Lever in Humans
An example the neck as it shifts from a position of flexion to a position of extension.
A Class 1 lever is the most versatile of all levers. It can afford a speed and/or force advantage.
© 2015 Thompson Educational Publishing, Inc.

9. 2nd Class Levers – “Wheelbarrow Levers”
resistance is located between the effort arm and the fulcrum. These levers multiply the force but the direction stays the same.

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A Class 2 Lever in Humans
An example is the ankle joint (the fulcrum) in combination with contraction of the gastrocnemius muscle (the effort).
This lever mechanism is capable of moving almost the entire weight of an individual (load) during plantarflexion (standing on one’s toes).
A Class 2 lever affords a force advantage: a
relatively small effort can lift a large load.
© 2015 Thompson Educational Publishing, Inc.

11. 3rd Class Levers - “Tweezers”
The effort force is located between the fulcrum and the resistance.

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A Class 3 Lever in Humans
An example 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 range of motion.
© 2015 Thompson Educational Publishing, Inc. 30