Biomechanics exam questions Flashcards
Explain the difference between random and systematic errors and give 2 exams of each
Random errors = errors which vary from video field to field such as joint markers moving out of the plane or the subject not always moving at 90 degrees to the camera
systematic errors= errors which stay the same from video field to field such as a joint marker being in the wrong place or the camera not being 90 degrees to the action
explain the difference between filming speed and shutter speed and why suitable values need to be chosen
filming speed= how many pictures per second a camera records where as shutter speed is how long the camera is exposed to light
usually 25 frames per second
type of sporting action and available light needs to be taken into consideration
fast sporting actions such as a golf swing - short shutter speed and high light needed
give the requirements for the equipment set up for successful video recordings, including the advantages and disadvantages of using video
camera mounted stationary on a tri[od
far as way as possible to the action to avoid perspective error
focal length adjusted to focus the image and the field of view should be adjust to the area being recorded
focal length kept constant
performer should move 90 degrees to the optical axis of the camera
joint markers - contrasting colour
unclustered background
suitable frame and shutter speed
immediate feedback
cheap
settings can be adjusted such as shutter
errors- during digitising, blurring of the image
locations of joint axes are only estimates
perspective error may be an issue where there is a discrepancy in the length between 2 objects of equal length when one is closer to the camera
genlocking - expensive system
what are CCD and CMOS
Image sensors
CCD - couple charged device, high quality low noise images, uses more power
CMOS- not as accurate, shutter will gradually move in a certain direction and expose 1 row at a time
Explain the force plate characteristics
linearity - maximum deviation of collected force plate data from a straight line
hysteresis - difference in output values seen during unloading and loading
should be minimised
e.g cause by deforming mechanical elements in a force transducer
range- must be adequate for application and adjustable
rang too small - output voltage will saturate
sensitivity- change in the recorded signal for a unit change in force input
sensitivity decreases with increasing range
cross talk - interference between recording channels
should be small
less than 3% of full scale deflection
Name the 2 requirement for quantitative kinematic data collection
accurate measurement of the position of the centre of rotation of each of the body segments
accurate time measurement for each position
What is the difference between quantitative kinematic and quantitative kinetic data
kinematic - displacement, velocity, acceleration
kinetic - anything related to forces. torque,
Give examples of kinematic and kinetic data collection methods
kinematic - video, ultrasound, electrogoniometry
kinetic - force platforms, pressure transducers
