MEASUREMENT Flashcards
Frame rate
How many individual frames are created each second
Shutter speed
How long each individual frame is exposed for
Intra participant variability
Variability within participants
Inter participant variability
Variability between participants
Intra observer variability
Variability in measurement or observation methods of single (within) researcher.
Inter observer variability
Variability in measurement or observation methods between multiple researchers.
Retroflective
A device or surface that reflects light back to its source with a minimum of scattering
High speed camera
A device capable of capturing moving images with exposures of less than 1/1,000 second or frame rates in excess of 250 frames per second.
Slow motion
The action of viewing video more slowly than it was made or recorded, so that the action appears much slower than in real life
What is stereo photogrammetry in movement analysis
“two”, photogrammetry: “photographic measurement”
List three limitations of stereo photogrammetry:
- Camera perspective: Markers / body locations can easily be obscured from view
- Marker identification (e.g. manual):Random error via subjective marker identification / Error prone to propagation as error exists in both camera images before position triangulation
- Difficult to model body segments in three-dimensions (due to above); limited use in biomechanical applications
List the two mains methods for calibrating stereo photogrammetry systems
- Checkerboard
* Calibration frame
Three-dimensional motion capture systems are an alternative data capture system to stereo photogrammetry, but what is it?
Three-dimensional motion capture systems are an alternative data capture system to stereo photogrammetry, but what is it?
What are depth cameras?
Consumer technology capable of three-dimensional measurement ‘out-of-the-box’
Low-cost (~£150) and easy-to-use
Depth information (structured light or time-of-flight) for each pixel (e.g. 2D and depth)
Why should we ensure that any 3D data captured systems is synchronised?
To ensure data captured from different sources reflect the same instant in time (i.e. measurements are synchronised)
How many individual frames are created each second.
frame rate
How long each individual frame is exposed for.
shutter speed
Variability within participants
inter observer variability
Variability between participants
intra observer variability
Variability in measurement or observation methods of single (within) researcher.
Intra participant variability
Variability in measurement or observation methods between multiple researchers.
Inter participant variability
A device or surface that reflects light back to its source with a minimum of scattering
Inter participant variability
A device capable of capturing moving images with exposures of less than 1/1,000 second or frame rates in excess of 250 frames per second.
high speed
The action of viewing video more slowly than it was made or recorded, so that the action appears much slower than in real life.
slow motion
what are requisites of data captured in sport and exercise?
accuracy validity precision or reliability objectivity minimal error propagation comprehensibility
define logical validity
(also known as face validity) – when this is obvious
define criterion validity
validate measures against accepted test or measurement standard (the criterion)
define concurrent validity
when two measurements are taken simultaneously
define external validity
the extent to which measurements emulate the real
world (see Brunswick, 1956 for review of ecological dynamics)
define reliability
Expresses the consistency of a test or measurement over time
define repeatability
how well an individual can repeat an experiment (e.g. intra-observer)
define reproducible
: how well an experiment can be reproduced (e.g. inter-observer)
define consistency
A reliable measurement can support validity: reliability is essential for validity
state some examples of human impacts
blunt force trauma, infrequent or high-force inmpacts such as commotio cordis in baseball.
Or chronic, repetitive loading the accumilation of low force impacts. e.g. medial tibial stress syndrome in running.
name some devices that measure human impacts.
force platforms and load cells.
pressure platforms
isokinetic dynamoeter.
An an indrect measure of human impacts can be by usiing an accelerometer.
Why is impact effected by inertia?
This is because the heavier the object the more resistant it is to having its motion changed. Mass is an intrinsic property and does not change or depend on what it is around (unlike weight it depends on gravitaional pull towards the centre of the earth).
Therefore the result of an impact depends on it’s inertia and initial momentum of both objects (assuming an inelastic impact).
Then during impacts we typically measure reaction force obtained by one of the objects. This accounts for Newtons thrid law.
How are impacts measured?
Newton’s third law. Reaction force.
What is dynamic friction?
Kinetic friction, also known as dynamic friction or sliding friction, occurs when two objects are moving relative to each other and rub together (like a sled on the ground).
How are impacts interpreted?
Vector quantities such as magnitude and direction.
State the mechanical derivatives that can also provide other ways of characterising impacts.
Acceleration- e.g. in tennis by measuring the impact acceleration that the racket endures this can help to identify the rackets sweet spot. This impact will be shown through vibrations. So we can use an accelerometer as an indirect measure of force to understand the impact force produced.
another example is zepp tennis which is a triaxial gyroscope and dual accelerometer.
Acceleration can also be used as a mechanical derivative to characterise head impacts. Such as the head impacts of CTD headform. This impact acceleration can then be used to design/re-design the properties of helmets. e.g. head impact crtierion HIC.
velcoity
momentum
impulse
energy
power
