force plate analysis Flashcards
Describe linearity with regards to force plate set-up?
linearity is in regard to the relationship between voltage and force.
hysteresis is the relationship between voltage and force during loading and unloading, and how they should be concurrent and linear rather than data jumping/jolting.
Describe hysteresiswith regards to force plate set-up?
Hysteresis is also regarding the voltage force relationship, but when force is decreased voltage should be proportional and decrease should be steady rather than bumpy or jolted.
With reference to range and sensitivity levels how might these settings change when collecting data for a vertical jump and a balance task? (2 marks)
Range for vertical jump would be high as the range of expected force is muh greater since a jump requires much more and generates much more force. Sensitivity is the link between recorded voltage and the force applied, as range increases sensitivity decreases, a low sensitivity is needed for balance tasks to pick up smaller changes in force, as the force range is low.
Explain what is meant by aliasing and why it could become a problem if collecting force from movements with high impacts (2 marks).
when we don’t use the right sampling frequency and it is set to low, aliasing occurs, this creates a false dsotrtion in recorded data, • You can lose impact magnitudes, or impact peaks altogether and valuable data.
Give two advantages and two disadvantages of using force plates to collect GRFs (4 marks)
We can accurately measure ground reaction forces accurately, to half a percent, and reliability too.
Set up is not as time consuming as other methods and the processing speed is very quick.
It can be used for varying tasks, balance, and explosive movements.
Cons:
Only one measure of centre of pressure, we don’t have anymore information about how pressure/force is dispersed over the whole foot.
Force plates can be very costly and thus may not be accessible.
Lack of Ecological validity, has to be done in the lab, is it still a natural movement
What varibales do we calcualte in excel afterward?
Net Force(N), Acceleartion (m/s2), Velocity (m/s), Displacment (m), Power (W), Flight time (s), Velocity at take off(m/s), Jump height(m), Peak power (W), Weight(N), Mass (kg)
Give two advantages and two disadvantages of using Kistler and Pasco force plates to collect GRFs (4 marks)
Kistler, - measruments and collection is very precise and accurate,
-not able to use in the field as not protable, lack ecological validity
PAsco- is cheaper and practically more portable,
-less information given as it is not 3D anlaysis
What is the eqations used in excel?
Net force = force - weight (N)
Acceleartion = force / mass
Velocity = accel (change in velocity) * time (+cell above)
Displacement = velocity * time (+Cell above)
Power = force * velocity
9) Describe linearity and hysteresis with regards to force plate set-up. (2 mark)
Lineartiy (increase in force/voltage) and hysteresis (decrease) are in regard to the linear relationship between voltage as a result of force production. This occurs when loading and unloading, and voltage should be concurrent and in a linear fashion rather than jolt/jump between readings.
With the help of the relevant equations, describe the process that you could go through to determine smoothed knee angular acceleration from raw knee angle data during running (5 marks)
first find raw angular velocity = change in knee ange / change in time
smoothed knee angle data = using an 11 point moving average for each cell
calculate smoothed knee angular velocity =
change in smoothed knee angle / change in time
calculate smoothed angular acceleration =
change in smoothed knee angular velocity / change in time
Describe the impulse-momentum relationship. (2 marks)
Impulse = change in momentum
momentum = mass * velocity
impulse = mass * change in velocity
this means impulse causes a change in momentum, resulting in a change in force.
As mass is constant, impulse production determines the velocity of a person/object.
Give an example of how we can synchornise video data with force data (2 marks).
Synchronisation lights in the view of the camera and which send a pulse to the force plate.
· OR synchronising any event which makes a clear spike on the force plate and can be seen in the video.
Impulse can be represented as the area under the force-time curve. State the equation for impulse. (1 mark)
Impulse = force x time
If we want to obtain power data from a force plate, explain why it is important that our participant is standing perfectly still on the force plate when data collection is started
- We need to know initial velocity (as all that can be calculated is change in velocity from the initial value)
- Making initial velocity zero is the easiest way to achieve this accurately.
