Lecture 16 + 17 - Intro into Kinetics : Gait Analysis Flashcards
what are the three laws of the study of forces that cause motion
- a push or pull : disturbing objects from their initial states (first law)
- a net force accelerates and object (second law)
- any force exerted is opposed by an equal and opposite force (third law)
1 N of force will accelerate a 1kg object by
1 m/s every second
force is a
vector quantity
what is GRF
ground reaction force
what is COP
centre of pressure
centre of pressure can be misleading, why
can be misleading as it is not a measure of pressure but a measure of position and refers to the average pressure point beneath the foot or feet
what are the objectives of gait
propel our bodies forward
to do so efficiently, requiring minimal energy expenditure
vertical ground reaction forces are a direct response to
centre of mass and its movement over base of support
what are horizontal ground reaction forces during gait
breaking and propulsion forces
what are the mediolateral ground reaction forces during gait
pronation and supernation of your foot
forces are sometimes normalised to body weight why
can be a way of comparing people with different body weights
the first peak of vertical forces during normal walking (heel strike to first peak F1) should be
1.2 times the persons body weight
what are the first bumps in initial contact (heel strike to first peak)
- first little bump may be first contact of heel
- then first peak should be 1.2 times body weight and is foot flat
what is happening during first peak F1 to trough F2 during vertical forces when normal walking
from flat food to mid stance
what happens to force during first peak F1 to trough F2
force is less than body mass
force is 0.6 times the persons body weight at trough
what happens to force during trough F2 to second peak (F3)
force should be almost equivalent to the first peak
F3 should be 1.2 times the persons body mass
what is happening during second peak F3 to toe off
gone from peak foot down to moving into the next step
what is happening to the foot during second peak to toe off
the foot is unloaded as the load is transferred to the opposite foot
during the second peak to toe off the time taken to off load the foot will related to
the speed of transfer of the weight to the front foot
during the second peak to toe off, the longer the offloading period from ..
from the back foot, the lower the first peak during loading on the front foot
what is the time of initial contact for the first peak like for an amputee gait
slower to accept weight in the amputee gait, slow to step onto it and quick to get off it
- see that it takes a little longer to get that heel strike foot flat, first peak
- more mediolateral shift than up and down
what are ground reaction forces
ground reaction force is the measured action - reaction force of our push against the ground
the shape of the vertical force component curve shows
confidence to load stance foot
height change of the centre of mass
indicates speed of movement
what are the vertical components of ground reaction forces during walking
- heel strike to first peak (F1)
- first peak (F1) to trough (F2)
- Trough (F2) to second peak (F3)
- second peak (F3) to toe off
what are the anterior posterior components of ground reaction forces during walking
- heel strike to posterior peak (F4)
- prosterior peak (F4) to crossover
- crossover to anterior peak (F5)
- anterior peak (F5) to toe off
what is happening during heel strike to posterior peak
after the initial claw back (if present), the heel is in contact with the ground and the body decelerates causing a prosterior shear force
prosterior peak (breaking force) should be
0.2 times the persons body weight
what is the middle of trough like for amputee gait
middle of the trough is similar space, they move to swing phase at same pace, using mediolaterial sway
what is time to last peak of vertical forces like for amputee gait
time of the last peak is very similar to the healthy
what can cause the claw back during heel strike to prosterior peak to be bigger or smaller
the surface we are walking on
why are breaking forces negative
because it is the resistant forces pushing back towards us when in contact with the ground
what is claw back
our initial heel strike and we pull back, reactive force thats moving just initially because we are adjusting to the surface
what situations may there be more claw back
walking on ice
what is happening in prosterior peak to cross over
the body begins to move over the stance limb, reducing the horizontal component of the resultant ground reaction force
at the crossover point the horizontal force
is 0, therefore the only force acting is that of the vertical ground reaction force
crossover should occur around
55% of stance phase
what is happening in crossover to anterior peak
swing limb is in front of us and we are lifting our heel to move forward
- the heel lifts and the foot is pushed down and back into the ground
- this has the effect of producing an anterior component of the ground reaction force, which propels the body forwards
the propulsion force of anterior peak should be
0.2 times the persons body weight
what is happening during anterior peak to toe off (and what happens to the anterior force)
the period of terminal double support, where force is now being transferred to the front foot and the anterior force, therefore reduces
during anterior peal to toe off the length of time the force takes to reduce and offload can
affect the loading during next foot contact
when looking at anteriror and prosterior ground reaction forces what would be seen if the person was speeding up
the second peak would be larger as need to have more propulsion compared to breaking in order to be accelerating
when looking at anteriror and prosterior ground reaction forces what would be seen if the person was trying to stop
much larger breaking force than propulsion force
what are the phases of mediolateral force during gait
start on the outside
as you start to plant your foot you role inwards and go into pronation
go through neutal
then propel off your great toe so go back pronation
what is the medialateral ground reaction force in early stance
greater lateral ground reaction force
what is the medialateral ground reaction force in late stance
greater medial ground reaction force
Pedotti digrams rely on the information provided by
force plates
the interaction of what can be shown on a pedotti diagram
vertical and anterior - prosterior force can be shown on pedotti diagram
to construct of pedotti diagram what is needed
need to know the vertical and horizontal forces and the position of the centre of pressure in the plane of interest for each moment in time