wk 6- kinetics and joint movements Flashcards
Define the study of kinetics
study of forces, moments, masses and accelerations, but without looking at position or orientation of the objects involved (kinematics)
first, second and third newtons law
- velocity of a body remains constant unless the body is acted upon by an external force
- the acceleration of a body is parallel and directly proportional to the net force and inversley proportional to mass
- the mutual forces of action and reaction between two bodies are equal, opposite and colinear
force platform does what
gives total force applied by the foot to the ground, does not show the distribution of different parts of this force on the walking surface
what does force plate measure
the electrical output signals produce
1. 3 componens of force vetocr, (vertical, lateral and fore aft)
2. two coordinates of the centre of pressure
3. moments about the vertical axis
why does ground reaction force magnitude increase/decrease during the gait cycle
why is it important to consider the direction (not just magnitude) of GRF vectors?
Discuss the magnitude and direction of ground reaction force vectors with respect to key events and periods in the gait cycle
during walking gait, the centre of mass rises during single support and falls during double support
since force = mass x acceleration, acceleration of centre of mass has an impact on the magnitude of forces exerted on the foot
why does vertical GRF look like an M
result of an upward acceleration of the centre f gravity during early stance, a reduction in downward force as the body flies over the leg in mid stance and a secon peak due to the deceleration as the downward motion is checked in late stance
vertical GRF during the gait periods IC, early stance, mid stance, late stance and terminal
A. At IC, force quickly rises as ipsilateral limb
accepts weight from contralateral limb
B. Forces rise above RESTING body weight during
early stance
C. Force falls below resting body weight during
midstance
D. Body weight rises above RESTING body weight
in late stance
E. During terminal double support, weight quickly
drops as body weight is transferred to the
contralateral limb
area under the curve
force time integral, force over time
Describe the clinical importance of moment data in gait analysis
Discuss internal and external joint moments with respect to key events and periods in the gait cycle
initial contact GRF- direction and magnitude
changes from upwards to upwards and back
loading response
increases rapidly in magnitude, its direction being upwards and backwards
opposite toe off
increase in vertical GRF magnotude, as now weight is being taken full on the stance limb
mid stance
Centre of pressure forward along the foot from foot flat onwards, moving into forefoot prior to heel rise
heel rise
cente of pressure forward due to ankle plantarflexion. now at forefoot and vector passes in front of knee joint
opposite initial contact
second peak of GRF, just prior to opposite initial contact
toe off
knee and hip flexion aided by backward position of vector. magnitude of the grf declines, alling to zero as the foot leaves the ground
GRF vector throughout gait
butterfly curve looking
moment is
A moment of force is multiplying magnitude of force by its perpendicular
distance from the fulcrum or pivot point
* Also referred to as “torque” or “turning moment
moment of force is generated around joints by 3
- ground reaction forces
- muscle activity
- tension of soft tissues (ligaments)
moment =
force x distance
types of joint moments
internal
1. active - muscle contraction
2. passive - tension of ligaments
external
-due to gravitational forces (GRF)
initial contact joint moments at the hip, knee and ankle
hip
internal extensor joint moment from contraction of hip extensors (external flexion moment -GRF)
knee
internal flexor moment, from contracture of hamstrings
external extensor moment (GRF)
then becomes external flexor moment once knee flexion has occurred
ankle
internal dorsiflexor moment from eccentric contraction of dorsiflexors
small external plantar flexor moment (GRF)
midstance joint moments at the hip, knee, ankle
hip
internal extensor moment dissipates and is replaced by an internal flexor moment
external moment moves from flexion to extension
knee
internal extensor moment- quads contract
force vector remains behind the joint causing external flexor moment
becomes external extensor moment due to forward progression of centre of mass (quads turn off)
ankle
increasing internal plantarflexion moment as the GRF vector moves from forefoot
external dorsiflexion moment (GRF)
terminal stance joint moments at the hip, knee, ankle
hip
peak hip internal flexor moment around opposite intital contact
decreasing external extension moment
knee
flexion of the knee in terminal stance leaves the knee joint in front of the force vector and changing the internal moment from flexor to extensor
therefore external moment is extension which changes to flexion just before contralateral initial contact
ankle
large internal plantar flexor moment created by a concentric contraction
force vector is anterior to ankle, creating large external dorsiflexor moment
