W29 (Pre-rec): Limitations of 2D Kinematics

Question 1

What are some benefits of using video based systems?

Answer 1

High speed capture
Can slow videos down
Allow us to look at movements in precise details
Athletes relate to it more than just stick bodies

Question 2

Give two examples of visual analysis:

Answer 2

2D (video film on iPad/iPhone etc)

3D (optoelectronic system)

Question 3

What are some benefits of using 2D recording?

Answer 3

Simple and cheap
Requires less digitising time (good for live feedback)
Fewer methodological problems

Question 4

What does 3D recording involve?

Answer 4

More complex procedure
Shows true body movements
Needs more equipment (more expensive)

Question 5

How would you choose between 2D and 3D recording?

Answer 5

Depends on what you want to look at, what time/space/resources you have
Can look at rotations etc.. in 3D

Question 6

Why do you want to be as far back as possible when filming?

Answer 6

Less likely to get knocked or bumped
Reduces parallax error
Position of object can look different depending on viewpoint

Question 7

What are the 3 planes of motion and how do the split the body?

Answer 7

Sagittal (left and right)
Transverse (top and bottom)
Frontal (front and back)

Question 8

What are the 3 axis of motion and where does the rod go through?

Answer 8

Frontal (from side to side)
Vertical/longitudinal (top to bottom)
Sagittal (front to back)

Question 9

What are some 2D limitations?

Answer 9

Too bright and hard to see

Too dark and can’t pick up markers

Question 10

What does frame rate mean?

Answer 10

Frequency that we sample at

Question 11

What does sampling rate mean?

Answer 11

Number of measurements taken per second
Essentially frequency
50 Hz = 50 pictures in 1 second

Question 12

How does 3D calibration work?

Answer 12

Using a wand

L frame defines X,Y,Z, corner sets origin point

Question 13

How does 2D calibration work?

Answer 13

Have to use calibration board/bar to tell video and software how long something is
As close to perpendicular as possible to reduce parallax error

Question 14

Describe the marker placement process:

Answer 14

Placed on body landmarks as not much subcutaneous fat

Need a marker at the joint then 1 proximal and 1 distal

Question 15

What is digitisation?

Answer 15

Process of identifying markers and landmarks, then converting the positions into coordinates

Question 16

What are the 3 types of digitisation?

Answer 16

Manual digitisation
Semi-auto digitisation
Automatic tracking

Question 17

Describe manual digitisation:

w some pros and cons

Answer 17

Used more for 2D than 3D
Have to go frame by frame and select all marker points
Non invasive
Time consuming/labour intensive
Follow through error if wrong by 1 pixel the first time

Question 18

Describe semi-auto digitisation:

w some pros and cons

Answer 18

Used more for 2D
Identify markers in first frame then software tracks them
Less time consuming
Markers can get lost and switched if limbs cross
Needs v specific lighting to not confuse markers

Question 19

Describe automatic tracking:

w some pros and cons

Answer 19

Used for 3D (in the labs)
Identify markers then pull over to QTM and tracks markers for entire movements
Less switching of markers (only if they are close in real life, won’t switch on software)
Some random reflections can add extra markers

Question 20

Compare 2D and 3D analysis

Answer 20

2D useful in the field, is very quick and easy to show instant feedback - have to make sure data is collected correctly
3D good bc every movement happens in more than one plane - don’t have to worry about rotation or having enough space as long as its calibrated
Less limitations for camera set up