Lecture 12 - Biomechanics of the Musculoskeletal System

Question 1

The MSK is a machine, define machine.

Answer 1

• a device or structure that changes the direction or magnitude of a force
• makes things easier
• ex: the lever (fulcrum/axis where lever rotates around)

Question 2

What is a lever?

Answer 2

• a long rigid segment with a point of rotation called the fulcrum
• the bones are the rigid segments
• the fulcrum is the joint

Question 3

If the lever is a vector, what are its 4 characteristics?

Answer 3

1. magnitude
2. direction
3. line of action
4. point of application

Question 4

what is torque?

Answer 4

• torque = force x perpendicular distance
• a vector
• use the right-handed method to determine direction

Question 5

what are the 3 factors that determine the muscle force?

Answer 5

1. amount of activation (from brain via motor nerve)
2. length of muscle (via the length-tension curve)
3. velocity of the muscle (via the velocity-tension curve)

Question 6

what is muscle memory?

Answer 6

• the amount of activation being sent is recognized/already known so you can perform skills well without really thinking
• this does not occur when trying new skills, you need to try several times and make adjustments in order to develop these connections

Question 7

how can you determine the muscle force direction?

Answer 7

• by its attachments
• by its wrapping point
• from insertion (distal segment) to origin (proximal segment)

Question 8

what is the line of action?

Answer 8

• drawn along the muscle vector
• determines the effect the muscle has on a joint
• can have two directions of pull/lines of action with 2 forces at the same attachment site

Question 9

how does lever arm length affect torque?

Answer 9

• shorter lever arm = less torque for the same amount of force

Question 10

how does lever arm change with joint position?

Answer 10

• lever arm = perpendicular distance
• direction changes as the joint angle/position changes

Question 11

how do wrapping points affect lever arm?

Answer 11

• lever arm is maintained at wrapping points
• constant lever arm throughout ROM

Question 12

why is the bodies force magnitude so large?

Answer 12

• muscles have shorter lever arms than external forces
• to make up for this, they need larger force magnitudes

Question 13

what is the stabilizing component?

Answer 13

• toward the joint center
• pulls the joints together

Question 14

what is the rotary/mobilizing component?

Answer 14

• at a right angle to the stabilizing factor

Question 15

how do the stabilizing and mobilizing components change the joint position?

Answer 15

• relative size of each will change the direction of pull
• not all pull is for rotation, some if for stabilization/dislocation