Dynamics

Question 1

Link Segment Model

Answer 1

Free Body Diagrahm of what someone looks like

Segment mass, COM, moment of inertia estimated from cadavers ie. Dempster, 1955

Question 2

Dynamics

Answer 2

Study of systems where acceleration is not zero

Question 3

What did a statics analysis tell us?

Answer 3

• Static tells tension needed to maintain a position
• Calculate about an axis/joint

Question 4

Linear Kinetics: Dynamic

Answer 4

F = ma
System is accelerating according to: ax, ay

Question 5

Angular Kinetics: Dynamics

Answer 5

ΣT = Iα
I = m * r^2
Sum of the moments will equal moment of inertiaangular acceleration of the system

Question 6

Inverse Dynamics

Answer 6

• Start at ground and move up (link segment)
• Method to derive net joint moments during human motion
• estimates “cause” of motion

Question 7

Torques and Walking - Inverse Dynamics

Answer 7

Tell you internally what is producing force
60% of walking cycle is stance phase
40% of walking cycle is swing phase
Ankle: Barely any torque, torque went negative (change in which muscle groups are active - tibialis anterior contract to control foot from slapping down), plantarflexors active the rest of the way through stance
Knee: Stance - flexor activity early, quad become active during loading eccentric, hamstrings take over later in cycle
Power = F x Velocity
Power = Torque x Angular Velocity (absorbing or generating power)
Ankle Power = DFs are absorbing eccentrically working, later in stance absorbing plantarflexion

Question 8

Forces acting on our model - Inverse dynamics

Answer 8

1. Gravity
2. GRF
   force plates
3. Net muscle, bone on bone, and ligament forces
   cannot parcel out which tissues are contributing to moment calculated using inverse dynamics
   if cocontraction of agonist, antagonist takes place, inverse dynamics yields net effect of both muscle moments. Can’t tell cocontraciton.
   Some have used electromyography and anatomical modeling to go further as to individual muscle, bony and ligamentous contributions

Question 9

Inverse Dynamics - Newton’s 3rd Law

Answer 9

there is an equal and opposite force acting at each hinge joint in our model

Calculations occur distally to proximally

For closed-chain activities, force and location of force are required at foot

Question 10

What measurements come from Dempster

Answer 10

Mass, Moment of Inertia

Question 11

What comes from moment capture?

Answer 11

Acceleration and angular acceleration, Segment COM location??

Question 12

What comes from force plate?

Answer 12

GRF

Question 13

Optimization

Answer 13

Computer solution of torques matches with muscle pulls. Solve for each muscle force pull in a time in motion. Static optimization: sloves for one point at a time.

Question 14

EMG and Static Optimization

Answer 14

EMG is flawed (doesn’t tell you force, only activation)

Static Optimization is as flawed. Most people doing research this way. This gives use the ability to study differences in tissue specific loading or how muscles produce force during movement