Video Analysis and Basic Anatomical Principles (week 3)

Question 1

state 4 facts about the anatomical starting position

Answer 1

1. upright standing position, facing forward, legs together, feet flat on floor, hands at sides, palms facing forward
2. helps in describing ‘geography’ of the body
3. how components relate to each other
4. generally in pairs: anterior + posterior, inferior + superior, medial + lateral

Question 2

state what it is meant by the key term - cardinal planes

Answer 2

the cardinal planes are the 3 imaginary perpendicular reference planes that divide the body in half by mass

Question 3

state the names, and function, of all three cardinal planes

Answer 3

1. sagittal/median plane - splits body left to right
2. frontal/coronal plane - splits body front to back
3. transverse/horizontal plane - splits body top to bottom

Question 4

in the anatomical position, where do all the cardinal planes intersect the body

Answer 4

the body’s centre of mass

Question 5

state what it is meant by the key term - axis

Answer 5

axis are infinite, imaginary lines which pass through joints

Question 6

state the names of all the anatomical reference axis, and the anatomical reference planes they pair with

Answer 6

1. mediolateral axis (and sagittal/median plane)
2. anteroposterior axis (and frontal/coronal plane)
3. longitudinal axis (and transverse plane)

Question 7

state the movements possible in the sagittal/median plane, mediolateral axis

Answer 7

1. flexion and extension

2. dorsi and planter flexion

Question 8

state the movements possible in the frontal/coronal plane, anteroposterior axis

Answer 8

1. abduction and adduction
2. eversion and inversion
3. lateral/side flexion (trunk)
4. scapula elevation and depression
5. ulnar and radial deviation (hand)

Question 9

state the movements possible in the transverse plane, longitudinal axis

Answer 9

1. rotation
2. internal and external rotation
3. pronation and supination
4. horizontal flexion/adduction + extension/abduction

Question 10

state what it is meant by the key term - sampling (frame) rate

Answer 10

refers to how many frames you can sample per second

Question 11

state 2 facts about sampling (frame) rate

Answer 11

1. standard video in UK works with standard video format, PAL (phase alternating line) - 25 frames, 50 fields
2. standard frame rate = 25 Hz

Question 12

state what it is meant by the key term - shutter speed

Answer 12

indicates how long the sensor is ‘open’ and exposed to light

Question 13

state 3 facts about shutter speed

Answer 13

1. low shutter speed risks blurred images if the movement is fast
2. faster shutter speeds can capture fast movements
3. however, high shutter speeds can lead to dark images

Question 14

state what it is meant by the key term - aperture

Answer 14

aperture influences the amount of light and depth of the field

Question 15

state 2 facts about aperture

Answer 15

1. large aperture = much light (smaller F-stop number) = worse depth of field
2. smaller aperture = less light (larger F-stop number) = better depth of field

Question 16

state the calculation to work out the F-stop number

Answer 16

F-stop = focal length (mm) / diameter of aperture (mm)

Question 17

state what it is meant by the key term - digital gain

Answer 17

digital gain can be used to increase image brightness. but, this is artificial and can make the image grainy (adding noise to the image)

Question 18

high speed video:

Answer 18

1. high speed video overcomes the limitations of low sampling rates (up to 10,000 Hz)
2. more light required = more expensive

Question 19

state the sampling rates required for the following activities: walking, running, football kick, tennis serve/golf swing

Answer 19

1. walking - 25-50 Hz
2. running - 50 - 100 Hz
3. football kick - 100 - 200 Hz
4. tennis serve / golf swing - 200 - 500 Hz

Question 20

state the two steps required to set up a camera for quantitative analysis

Answer 20

1. camera positioning/orientation (minimising perspective error)
2. calibration (allow scaling the video to real world coordinates)

Question 21

state what it is meant by the key term - perspective error

Answer 21

perspective error is the error caused in the position of an object when the viewing angle is not perpendicular to the object

Question 22

state the two considerations for the first step of setting up a camera for quantitative analysis

Answer 22

1. camera-object distance as far as possible

2. camera perpendicular to the plane of motion (pan, tilt, and roll)

Question 23

explain the calibration step (step 2) in setting up a camera for quantitative analysis

Answer 23

need to record a ‘known distance’ so you can scale the video (pixels) to real world distances, to obtain 2D/3D co-ordinates

Question 24

state 2 benefits of the use of video camera analysis over that of online motion analysis

Answer 24

1. flexibility (can be used in more environments - like water)
2. allows for visual feedback for the performer (permanent record)
3. low cost
4. minimal interference to the performer (eg - reflective markers)

Question 25

equipment considerations: (5 things)

Answer 25

1. camera
2. recording and storage devises
3. playback system
4. co-ordinate digester (to allow movements to be taken from the video images)
5. processing and analysis software

Question 26

state 5 video camera considerations:

Answer 26

1. picture quality
2. frame rate
3. manual high speed shutter
4. manual aperture adjustment
5. light sensitivity
6. gen-lock capabilities
7. recording medium (eg - tape or hard drive)

Question 27

equipment set up process for 3D video analysis - 5 steps:

Answer 27

1. mount cameras on stable tripods and avoid panning
2. position cameras for optimal positioning of landmarks
3. ensure control points are visible and recorded by all cameras
4. align the performance with the axis of the global co-ordinate system
5. make provision for shutter synchronisation and event synchronisation

Question 28

state what it is meant by the key term - biomechanics

Answer 28

biomechanics is the study of the structure and function of biological systems by means of the methods of mechanics

Question 29

state what it is meant by the key term - perspective error

Answer 29

perspective error is error caused in the position of an object when the viewing angle is not perpendicular to the object

Question 30

state the two considerations to be mindful of to reduce perspective error

Answer 30

1. camera object distance as far as possible

2. camera is perpendicular to the plane of motion (pan, roll and tilt)

Question 31

state what it is meant by the key term - video

Answer 31

a video is a sequence of images taken at constant time intervals. it is a 2D representation of a 3D scene

Question 32

high speed video allows for ‘greater’ what ?

Answer 32

greater temporal resolution

Question 33

explain temporal resolution (in relation to high speed video)

Answer 33

high speed video takes more frames per second than standard video which means that the time interval between each frame is smaller. This means that you are more likely to see specific events within a movement pattern as these events are less likely to occur at a time inbetween frames

Question 34

state what it is meant by the key term - focal length

Answer 34

focal length is the distance between the centre of a lens, or curved mirror, and its focus

Question 35

what is the difference between sample rate (FPS) and shutter speed ?

Answer 35

• Frame rate refers to the number of individual frames that comprise each second of video you record
• Shutter speed refers to the amount of time that each individual frame is exposed for