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Lecture 6

MOVESCI 110 Lecture 6: Biomechanics Levers and Forces

3 pages79 viewsFall 2018

Movement Science
Course Code
Kathy Kern

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Lecture 6
Musculoskeletal system thought of as series of simple machines balanced at
COG (center of gravity) with internal and external forces acting upon it
Machines function in four ways:
o To balance multiple forces
o Enhance force to overcome resistance
o Enhance speed of movement so resistance can be moved further
(increasing ROM/Range of Motion)
o Alter resulting direction of applied force
Musculoskeletal system provides for 3 machines
o Levers, Wheel/Axles, Pulleys (lever most common in body)
Levers: rigid bars that move around axis of rotation or fulcrum (bones move
around joint)
o Forces (supplied by muscles) cause movement
o Levers are about efficiency most economical way to move body/body
o Resistance is often weight of body segment/whole body (could be external
o Force is almost always the force of a muscle contraction
First Class Lever: axis lies between force and load (effort and resistance)
o Advantage: balance, magnify effort, increase speed/ROM
o Example: neck - FAR (force-axis-resistance)
Second Class Lever: resistance between axis and effort
o Advantage: magnify effort (small force moves a lot of weight)
o Example: ankle plantar flexion standing on toes - ARF (axis-force-
Third Class Lever: effort between axis and resistance
o Advantage: speed and ROM
o Example: bicep curl AFR (axis-force-resistance)
Movement about a joint is always rotational
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