1. Levers
kinesiology unit 7

2. Anatomical Lever Systems
Definition of a LEVER:
A Lever is a rigid object that revolves around a fixed point called a fulcrum or axis.

3. The segments are the straight lines between joints.
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.

4. Functions of skeletal levers:
Increase effort produced when force is exerted on a body
Increase the distance through which a body can be moved in a given time

5. 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.

6. The ration of the length of the force arm to the resistance arm.
Mechanical Advantage
Definition of the MECHANICAL ADVANTAGE
The ration of the length of the force arm to the resistance arm.

7. Advantage of Using Levers
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.

8. 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.

9. Fulcrum between resistance and applied force
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)

10. 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 = effort Resistance = mass of head
Muscles of lower back
Very few first class levers in the human body

11. 2nd class lever FRE Resistance always closer to fulcrum
NB for strength!!!!
Poor for ROM and speed
E.g. Standing on toes: toes = fulcrum Calf muscle = effort Resistance = mass of body

12. 3rd class levers FER Effort is closer to fulcrum
Most common in human body
Good for speed and ROM
Poor for strength
E.g. Elbow Elbow joint = fulcrum Biceps = effort Resistance = lowering the arm

13. So… The effort (E) in a muscle will depend on:
How far the muscle is away from the fulcrum  the further away the muscle attaches from F = greater ability to generate force
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

14. 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

15. There are three classes of levers
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.
QUESTION:

16. End of Unit