Week 8 Flashcards
What is the normal range for impact peak in GRF during running
1.5 - 2 BWs
What is the normal range for active peak in GRF during running
2 - 3 BWs
What is the normal range for loading rate in GRF during running
50 - 100 BWs/sec
What is a moment
Moment or moment of force are a synonym for torque
What is torque
The ability of a force to cause rotation about an axis
What is a joint moment
ability of a force either internal or external to cause rotation about a joint
Equation of torque is
Moment arm x Force
How can we tell how much force or torque is acting on each joint (how can we measure it)
Embed Force Sensor - direct
Inverse dynamics - indirect
Embed force sensor is usually used on
Amputee population
Inverse dynamics is
An indirect estimation of force and torque acting on a joint based on several measurements
What do we need to collect from inverse dynamics
Kinematics of each segments
Ground reaction forces
Anthropometrics of each segment
Receiving Kinematics of each segments involves finding the (Inverse dynamics)
Position
Velocity
Acceleration
Receiving Ground reaction forces involves finding the (Inverse dynamics)
Anterior/posterior
Medial/lateral
Vertical
Receiving Anthropometrics of each segment involves finding the (Inverse dynamics)
Length
Mass
Center of mass location
Moment of inertia
How would you get mass / COM location for each segment
Use table of values based on cadaveric studies from research study
Then:
- Look at definition of body segment
- Segment weight compared to body weight as %
- Look at center of gravity from proximal end
What is mass
A quantity expressing a bodys tendency to resist LINEAR acceleration
What is moment of inertia
A quantity expressing a bodys tendency to resist ANGULAR acceleration
Force =
Mass x Acceleration
Torque =
Moment of Inertia x Acceleration
Or
Force x moment arm
As you go up the leg
There are more estimates involved
This is because you use one estimate for the next estimate
What are the steps for inverse dynamics
- Use GRF and foot information (Kinematics and anthropometrics) to estimate the internal ankle forces and moments
- Internal ankle forces and moments then used with SHANK information to estimate internal knee forces and moments
- Internal knee forces and moments then used with THIGH information to estimate internal hip forces and moments
What do you end up with in inverse dynmaics
At each lower extremity joint (ankle, knee and hip):
Net internal joint force
Net internal joint moment
What units for torque
N*m
Normalised to N*m/kg
Internal forces and moments are mainly caused by
Muscle contractions
Passive soft tissue stretch/tension
Articular reaction forces
Net internal force + net external force =
Mass * acceleration
Net internal moment + net external moment =
Moment of inerta * acceleration
External forces are
GRF
So when we do inverse dynamics we collect
Internal forces and moments
What is often reported in literature
External moment since this is what represents the torque applied to the joint by external forces
What counteracts external torque created by the GRF
Why
Internal torque
The muscles react and contract to create an internal torque to counteract the external torque
Reduces the external load on the joints - injury
The counteracting nature largely related to
What also is a factor
The interaction between the GRF and the joint
e.g. direction of GRF and what it causes to happen at the joint
Other joint forces and moments will also play a factor
e.g. the forces and moments at the ankle could play a factor in the force and moments of the knee
Muscles and other soft tissue structures will…
Counteract the external moment to produce the internal moment
High external knee varus moments have been linked to
Increased pain and rate of disease progression in patients with knee osteoarthritis
Torque, moment, and moment of force are all synonyms and mean the same thing
True
Inverse dynamics is a method of directly measuring the amount of force and torque is applied to a joint
False
Which of the following pieces of information is NOT needed to perform inverse dynamics
Walking/Running velocity of the participant
How do we estimate segment weight and center of mass location
This information is estimated by using guidelines published from cadaveric studies
When performing inverse dynamics, which joint force and moment are estimated first
Ankle
Joint moments are normalized by body mass for what reason
So that we can compare data across participants
During inverse dynamics we are actually solving for what
The internal joint forces and moments
The external joint moment represents the torque applied to the joint by other external forces
True
The vertical ground reaction force is generally the only force we can directly measure with inverse dynamics
False
Higher joint moments for what joint and plane have been strongly associated with a higher rate of disease progression in knee osteoarthritis
Knee varus
