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The lever system. Module 2- Principles of Biomechanics. Lever. Movement occurs when muscle pulls on bone, rotating it about a joint Movement occurs when force acts on a lever about an axis (fulcrum) Distance between axis and point of force application is the moment arm
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The lever system Module 2- Principles of Biomechanics
Lever • Movement occurs when muscle pulls on bone, rotating it about a joint • Movement occurs when force acts on a lever about an axis (fulcrum) • Distance between axis and point of force application is the moment arm • Typically two forces acting on lever, for our sake they will be known as the force arm and the resistance arm • Two forces=two moment arms
Lever • Rotating about an axis, therefore producing rotational force • Rotational force is called torque • Torque is the product of the force and the moment arm • See Saw example
Mechanical Advantage • The ratio of the moment arm through which an applied force acts to that through which a resistive force acts. A mechanical advantage greater than 1.0 allows the applied (muscle) force to be less than the resistive force to produce an equal amount of torque. A mechanical advantage of less than 1.0 is a disadvantage in the common sense of the term. • Two ways to increase mechanical advantage • Increase Force Arm • Decrease Resistance Arm
Lever Classes • 1st Class • Force and resistance are on opposite sides of the fulcrum • See saw • 2nd Class • Force and resistance are on the same side of the fulcrum (resistance is between fulcrum and force) • Wheelbarrow • Force will always be less than resistance
Lever Classes • 3rd Class • Most common type in the body • Force and resistance are on same side of fulcrum (force is between axis and resistance) • Force will always have to be greater than resistance • Biceps example • Speed advantage • In the “real world” the force arm and resistance arm are not constant through a range of motion
Figure 4.9 Reprinted, by permission, from Gowitzke and Milner, 1988.
Figure 4.6 Reprinted, by permission, from Gowitzke and Milner, 1988.