Kinetics Flashcards
What two forces are not the same?
Bone on bone force and joint reaction force
Can you directly measure forces?
No > ESTIMATE from kinetic, kinematic + anthropometric data combined w/a biomech model and GRF
In link-segment modelling joints are modelled as
hinges or ball and socket joints
What body forces are present in link-segment modelling?
- Gravitational
- Ground reaction (external)
must be measured through force transducer
distributed over an area - acts at a point CoP
force plate gives CoP, GRF and moment - Muscle + ligament
net effect of agonist and antagonist muscles (cocontraction)
Bone-on-bone forces
- actual forces seen across articulating surfaces
- include effect of muscle activity
- active muscle contraction creates compressive (and possibly shear) forces
What are joint reaction forces?
reaction forces between segments which arise when the model is broken at the joints into segment parts
Force transducer
measures force which causes strain
GRF
- principle external force when walking
- 3D vertical plus 2 shear
- acts from CoP
Measuring GRF
may measure pressure underfoot, Tekscan in-shoe plantar pressure measurement system
CoM
location in 3D of weighted sum of CoM’s in all segments
CoG
vertical location of CoM
CoP
location action of GRF, neuromuscular response to imbalance of CoM and has to remain in base of support
What type of motors are muscles?
Linear motors that give rise to additional compressive and shear forces
What type of motors does link-segment modelling assume for muscles?
Torque motors. As joints are modelled as hinges the moment of a force acts as a torque motor
Muscle force indeterminacy
estimating muscle forces is difficult because many muscles contribute to a net moment
