Levers and Pulleys

Question 1

What determines Mechanical Advantage?

Answer 1

• The location of forces and axis
• MA = Force Arm/Resistance Arm
• Determines how “effective” a lever wil be

Question 2

What are the 3 purposes of a lever?

Answer 2

• Change direction of force
• Magnify force
• Magnify displacement )ROM) or velocity

Question 3

What is the musculoskeletal system designed for?

Answer 3

ROM and velocity, not force (poor MA)

Question 4

1st Class Lever

Answer 4

• F-A-R “Far Out”
• Accomplishes all purposes of a lever depending on the location of the axis relative to the 2 forces
• Change direction
• Magnify ROM and Velocity
• Magnify F

Question 5

2nd Class Lever

Answer 5

• A-R-F “Real Dogs”
• Mech Adv >1: Magnify force
• Atypical in the human body

Question 6

3rd Class Lever

Answer 6

• A-F-R
• Most common type in the human body
• Mech Adv <1: magnifies ROM & Velocity

Question 7

How do we change torque?

Answer 7

• Train for strength (increase force output)
• Alter muscle insertion sites (change moment arm, surgical intervention)
• Use a lever (Can change how force is applied and where relative to axis

Question 8

Pulley

Answer 8

Modify angle of pull
- Places line of pull in a more effective position for a desired action
- Ex: Anatomical pulley (Quad over patella)
- - Gives a larger rotary component with a patella
- W/O a patlla way more compression results in cartilage wearing out faster due to higher forces

Question 9

Why are rearfoot runners more likely to experience need pain?

Answer 9

Patellafemoral forces are higher so the quads have to work harder as a result of rearfoot striking. Without patella no rotarty force, therefore compression force gets signficantly higher and results in quad having to work harder. Bending the knee decreases the GFR.