Module 9 - Muscle Moment Arm & Joint Geometry

Question 1

When is muscle lengthening velocity not constant?

Answer 1

• When joint angular velocity is kept constant

Question 2

What can biomechanical models based on the anatomy of the muscles and joints be used for?

Answer 2

• Orient clinical interventions
• Guide training practices

Question 3

Why can joint geometry be considered as important as the force-length relationship?

Answer 3

• Muscle length changes with joint angle
• ????

Question 4

What is the equation of moment of force?

Answer 4

Moment of Force = d x F

Question 5

in real-world activities, what does ‘strength’ represent?

Answer 5

• Moment of force (or torque)

Question 6

Why can we not assume that someone is strong because their muscles produce a lot of force?

Answer 6

• Muscle force is only one parameter contributing to moment

Question 7

Does the muscle moment arm change during movement?

Answer 7

NO

Question 8

What would be required to identify the angle between muscle line of action and joint axis of rotation?

Answer 8

• Real-time imaging of the muscle and bones

Question 9

What can be used to estimate the muscle moment arm?

Answer 9

• Joint angle
• Distance between muscle insertion and joint centre of rotation

Question 10

What is the law of sines?

Answer 10

a/sin a = b/sin B = c/sin Y

Question 11

What happens with a moment of force when force is held constant?

Answer 11

-It varies as a function of joint angle
- d changes based on joint angle

Question 12

What does a moment of force output depend on?

Answer 12

Muscle
- PCSA
- Muscle Fiber Length
- Working Range of Muscle
Joint Geometry

Question 13

How do muscles strengthen?

Answer 13

• when they are subjected to high forces

Question 14

Why does understanding how muscles strengthen help with training adaptation?

Answer 14

• Understanding whether to perform exercise at joint angle that produces most muscle force or at angle where person is strongest

Question 15

What does isokinetic dynamometer machines measure?

Answer 15

• moment of force: does not change with variation in pad placement

Question 16

Why is force not measured with a isokinetic dynamometer machine?

Answer 16

• would need to account for the position of the pad with respect to joint

Question 17

What is used to measure constant moment of force across different joint angles during movement at constant velocity?

Answer 17

• Isokinetic Testing Machines
• Using Visual feedback

Question 18

Does muscle moment arm vary during motion?

Answer 18

• Yes

Question 19

Does a constant moment of force mean constant muscle force?

Answer 19

• No

Question 20

What angular velocities are the Isokinetic Testing Machines usually set to?

Answer 20

• 300 degrees/s

Question 21

What is the angular velocity of throwing a ball?

Answer 21

• 6000 degrees / second

Question 22

What is the angular velocity of jumping?

Answer 22

• 700 degrees/second

Question 23

What is the angular velocity of a whiplash injury?

Answer 23

• 600 degrees/second

Question 24

What needs to be integrated together to understand muscle function?

Answer 24

• estimation of muscle length and moment arm
• Force-length relationship
• Force-velocity relationship