module 9

Question 1

what does strength represent in real-world activities?

Answer 1

represents moment of force (torque)
- manifestations of moment force generation by the musculoskeletal system (M=dxF)

Question 2

why can we not assume someone is strong simply bc their muscles produce large forces?

Answer 2

• muscle force is only one parameter contributing to moment - also need to take into account thier moment arm

Question 3

how does the moment arm relate to force

Answer 3

• alters the ability to generate a moment of force
• moment arm changes during movements depending on joint angle

Question 4

why are moment arm and joint geometry examples difficult to relate to real-world applications?

Answer 4

the angle between muscle line of action and joint axis of rotation is difficult to estimate - would require real-time imaging of the muscle and bones
- other hand: joind angle is readily measured
- can only estimate moment arm with info about joint angle, and distances between muscle insertion and joint centre of rotation (using the law of sines)

Question 5

why is moment arm important?

Answer 5

muscle force generates a moment of force acting around a joint - evaluation of strength in humans refers to moment of force measurement
- given that M=dxF, it will also vary as a function of joint angle if F is constant (d changes as function of joint angle)

Question 6

what is muscle force a function of?

Answer 6

1. function of d (moment arm)/joint geometry
2. muscle length (F-L relationship - CB overlap)
3. velocity of muscle shortening (F-V relationship)
4. activation of muscle (MU recruitment, muscle fiber type)

*complex interation between mm mechanics and joint geometry - depends on the muscle (PCSA, mm fiber length, working range) and joing geometry

Question 7

muscle moment arm application for training?

Answer 7

muscles are strengthened when subjected to high forces

Question 8

isokinetic dynamometer machines?

Answer 8

measure moment of force not force (would need to account for the position of the pad with respect to the joint)

Question 9

joint geometry testing?

Answer 9

1. isokinetic machines: mvmt at constant velocity - may produce constant moment of force (visual fb)
   - hard to interpret with repect to f-v curves
   - max angular velocity of these machines is much lower than angular velocities produced during human activities - limited to 300 deg/s (throwing a ball = 6000 deg/sec, whiplash injury = 600 deg/s, jumping = 700 deg/s)