Analyzing Human Movement: Dynamic Analysis Part 4 & 5

kinetics

the study of forces that produce, start, stop, or modify motion

analysis of the forces that act to cause or produce motion

kinematics

the description of motion without regard to forces that cause the motion

varus joint alignment

distal end is angulated inward
toward midline
(knee varus: ankle is toward midline)

valgus joint alignment

distal end is angulated outward
away from midline
(knee valgus: ankle is away)

center of pressure

the center of pressure represents the sum of all forces acting between an object and its supporting surface
the point of action of the resultant force vector on a force platform

external moment is determined base on

GRF

eccentric

work is performed on the muscle
negative power

concentric

muscle performs works
positive power

isometric

no work is performed because no displacement

what is the relationship between power and velocity

power and velocity have a positive relationship
as velocity increased, power increased because angular power is the product of the net internal moment and joint angular velocity

power formula

work /time
- The rate of work
P= W/t
- Product of the net internal moment and joint angular velocity
- Watts
- Net transfer of energy between active muscles and external load

work

Force X displacement
- Force or torque operates over some displacement
- Measure of energy flow from one body to another
- In the direction of the applied force
- No displacement = no work
- W = Fd or W= Td
Joules
- For calculations, convert degrees to radians

negative power

- Work done by the external load against the muscles
- Rotation of segment opposite direction of internal torque/moment
- Eccentric muscle activation
- Stretching of connective tissues
- Energy absorption

positive power

- Work done by the muscles against external load
- Rotation of segments same direction of internal torque/moment
- Concentric muscle activation
- Release of energy from previously stretched tissues
- Energy generation

what variables are needed to estimate the force produced by an individual muscle

joint center
data from EMG
ground reaction force

on a force platform, the resultant GRF vector has its point of action at the

center of pressure

inverse dynamics

technique to estimate the net joint forces and muscle net moments during dynamic conditions
INDIRECT

analysis begins at the distal end of a segment (GRF)