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Levers

KINESIOLOGYUNIT 7

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ANATOMICAL LEVER SYSTEMS

• Definition of a LEVER:

A Lever is a rigid object that revolves around a fixed point called a fulcrum or axis.

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• Application of a LEVER

The Human Skeleton consists of a series of bony segments linked together at a pivot point called a

joint.

The segments are the straight lines between joints.

When a muscle contracts, the segments move about a pivot point.

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FUNCTIONS OF SKELETAL LEVERS:

1. Increase effort produced when force is exerted on a body

2. Increase the distance through which a body can be moved in a given time

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RESISTANT ARM & FORCE ARM

• Definition of the RESISTANT ARM

The length of the lever between the fulcrum and the resistance.

• Definition of the FORCE ARM

The length of the lever between the fulcrum and the applied force.

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MECHANICAL A

DVANTA

GE

• Definition of the MECHANICAL ADVANTAGE

The ration of the length of the force arm to the resistance arm.

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ADVANTA

GE OF U

SING LE

VERS

• First

The lever serves to increase the effect a force has on an object to which it is being applied.

• Second

The lever increases the speed with which an object is moved.

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• If the force arm is longer than the resistance arm, the lever will increase force produced.

• If the resistance arm is longer than the force arm, the lever will increase in speed.

Example:

Swinging a tennis racquet increases resistance arm, resulting in an increase in speed of striking point, but

requiring greater force to produce movement.

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TYPES OF LEVERS

• First Class Lever

Fulcrum between resistance and applied force

• Second Class Lever

Fulcrum at one end of lever with resistance closer to fulcrum (eccentric contractions)

• Third Class Lever

Fulcrum at one end of lever with force closer to fulcrum (concentric contractions)

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1ST CLASS LEVER

• EFR

• Fulcrum not always in the middle…can be closer to effort or resistance

• E.g. Holding up head:Atlas = fulcrum Occipital bone = effortResistance = mass of head

• Muscles of lower back

• Very few first class levers in the human body

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2ND CLASS LEVER

• FRE

• Resistance always closer to fulcrum

• NB for strength!!!!

• Poor for ROM and speed

• E.g. Standing on toes: toes = fulcrumCalf muscle = effortResistance = mass of body

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3RD CLASS LEVERS

• FER

• Effort is closer to fulcrum

• Most common in human body

• Good for speed and ROM

• Poor for strength

• E.g. ElbowElbow joint = fulcrumBiceps = effortResistance = lowering the arm

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SO…

• The effort (E) in a muscle will depend on:

1. How far the muscle is away from the fulcrum the further away the muscle attaches from F = greater ability to generate force

2. How far the load ( R) being moved is from the fulcrum load further away = greater amount of Effort needed to be put in by muscles

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• Humans are designed for speed and Rom rather than strength because of our skeletal structure have to put in more effort than we put out/ move body part

• Therefore, humans are mechanically disadvantaged…High cost in force = the tension in muscles is many times greater than the force we exert on the environment

• Therefore humans have a poor force – velocity relationship:The quicker the muscle is asked to contract = the less force it can generate

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QUESTION:

There are three classes of levers. Describe the

important characteristics of each lever type. Comment

on how the type of lever involved changes with the type of muscle contraction

being performed.

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END OF U

NIT