module 8

Question 1

name 4 factors influencing force production

Answer 1

1. mm architecture (fiber arrangement, PCSA, mm fiber types)
2. neural factors (increasing firing rate of MU, orderly recruitment of MUs)
3. Force-length relationship (active and passive comps)
4. force-velocity relationship (high velocity generates low force - for con actions)

Question 2

why is joint geometry important in infleuncing force production?

Answer 2

in the musculoskeletal system, muscle generate and transmit force via tendons to the bones
- bones ar enot free to move in space
- bones are constrined to rotate about a joint axis
- hence, linear actuator (muscle) transmits forces to an angular musculoskeletal system (moment arm and moment of force are crucial)

Question 3

how does muscle length work with joint geometry?

Answer 3

can estimate muscle length based on joint geometry
- needs to be known: 1. distances between muscle insertion and joint centre of rotation - estimated (MRI) 2. joint angle - measured (motion capture)
distances do not vary with human movement and can be done with law of cosines (c2 = a2 + b2 - 2abcos(y))

Question 4

what is the effect of muscle fiber length on active ROM?

Answer 4

short fibers: full flexion and extension are at smaller degrees
*better ROM with flexion

long fibers: full flexion and extension are at longer degrees
*larger ROM with extension

Question 5

joint geometry: isokinetic testing machines?

Answer 5

*aims at keeping angular velocity constant during testing
*controlled, gives rigor
*participants can push as hard as they want and machine will generate a movement at a constant velocity

*but constant angular velocity doe snot equate to constant muscle lengthening or shortening
*very difficult to interpret isokinetic data with respect to f-v curves (length not changing at constant value = not constantly at same point of f-v relationship) - would be helpful to model