11.2 Levers in the Human Body PDF

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Kinesiology Introduction to Excercise Science...

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Maria Clara Deray PSK4U1 Mr. Backus 11.2 Levers in the Human Body

(A) Types of Levers First Class Lever Diagram of a first-class lever: E = Effort (or Force) R = Resistance AF = Applied Force

Everyday example of a first-class lever: The Class 1 lever is used in field lacrosse and field hockey. In both sports, the forceful pull of the hand of the hand at the end of the shaft of the stick (the effort) around the fulcrum (where the other hand is located about midway down the shaft) moves the ball (the resistance load). Example of a first-class lever in the human body: An example is the neck as it shifts from a position of flexion (such as when a person is looking straight ahead) to a position of extension (such as when a person is looking up). The contraction of the trapezius muscle permits extension of the head.

Second Class Lever Diagram of a second-class lever:

F = Fulcrum E = Effort (or Force) R = Resistance AF = Applied Force

Everyday example of a second-class lever: The fulcrum, load, and effort force are arranged similarly when using a wheelbarrow, thereby allowing a person using it to move a large load with a relatively small amount of effort. Example of a second-class lever in the human body: The ankle joint, when used as the fulcrum in combination with contraction of the gastrocnemius muscle (the effort), is capable of moving almost the entire weight of an individual (the resistance load) while moving to a position of standing on one’s toes.

Third Class Lever Diagram of a third-class lever:

F = Fulcrum (triangle) E = Effort (or Force) R = Resistance AF = Applied Force

Everyday example of a third-class lever: This type of lever enhances the speed of movement (that is, it provides a speed advantage), allowing relatively light resistance loads to be moved through a greater range of motion. In this situation, the magnitude of the effort force is larger than that of the resistance load. Common examples of third-class levers include squash racquets, cricket bats, and snow shovels. Example of a third-class lever in the human body: The Class 3 lever is the most common type of lever found within the human body. With this type of lever, the muscular force (or effort) is applied between the fulcrum (joint) and the resistance load. A person performing a bicep curl, for example relies on the third-class lever mechanism created by the insertion of the biceps muscle on the radius in combination with the elbow joint.

Movement:

Effort Force (E)

Fulcrum/Axis (F)

Resistance (R)

Knee extension

Quadriceps

Knee joint

Lower leg

Deltoid

Shoulder joint

Arm

Triceps

Elbow joint

Forearm/hand

Class of lever 3

Shoulder adduction Class of lever 3

Elbow extension Class of lever 3

Gluteus maximum

Hip joint

Leg

Scapular elevation

Levator scapulae

Acromioclavicular

Scapula

Class of lever 3

(with the help of

joint

Hip extension Class of lever 3

trapezius)...