Planar Kinematics

Question 1

Factors to consider regarding movement speed

Answer 1

1. faster movement requires higher sampling rate

Question 2

What type of signal does A and B represent?

Answer 2

A. Analog
B. Digital

Question 3

Which steps of the digitization Process does each letter represent?

Answer 3

A. Physiological Signal
B. Sample Hold Circtuit
C. Digital Encoder
D. Computer Clock
E. Computer Memory
F. Computer Storage

Question 4

Sampling Rate

Answer 4

speed at which encoder captures samples and converts to digital code (Hz)

Question 5

Typical frequency of physiological signals

Answer 5

15hz

Question 6

what are Hz?

Answer 6

hertz: 1 cycle/ second

Question 7

Motion analysis sampling rate (units)

Answer 7

pictures/sec

Question 8

force/ muscle activity sampling rate (units)

Answer 8

volts/sec

Question 9

sampling rate for most non image signals (units)

Answer 9

volts/sec

Question 10

Fourier Transform Function

Answer 10

Tool for determining the frequency content of a signal
-transforms signal into combo of sine and cosines
-frequency domain NOT time domain

Question 11

What do graphs A and B represent?

Answer 11

A. Time
B. Frequency

Question 12

What does A and B represent?

Answer 12

A. Sine Wave
B. Cosine wave

Question 13

Nyquist Sampling Theorem

Answer 13

A signal must be sampled at a frequency greater than AT LEAST twice the highest frequency present in the signal itself.
-Generally 4-5 times higher

Question 14

What happens if the sampling frequency is two low?

Answer 14

Aliasing- true signal is not reproduced

Question 15

what happens if the sampling frequency is too high?

Answer 15

unnecessary data.

Question 16

Point Mass

Answer 16

Center of mass in kinematics

Question 17

What does a Link Segment utilize?

Answer 17

Combines rigid body assumption

Question 18

Wobbling mass

Answer 18

effective impedence

Question 19

General Considerations for type of imaging used?

Answer 19

1. Size of image or model
2. whole body or segment
3. discrete measure? (foot angle at toe off)
4. continuous measure (foot angle throughout stride)
5. linear, angular, combination?

Question 20

2 D Assumptions

Answer 20

1. Motion is assumed to be planar
2. Saggital plane movement
3. Frontal plane movement

Question 21

2 D motional analysis limitations

Answer 21

-each camera only sees a single 2d image
-Depth cannot be judged (single camera assumes everything is in the same plane)

Question 22

Critical Assumptions of 2D analysis

Answer 22

-Single Plane
-Calibrated Movement

Question 23

2 D calibration

Answer 23

1. at least 2 points separated by known distance
2. calibration in both vertical and horizontal directions is best
3. Defines global coordinate system (lab axes)

Question 24

sfu= L/Lu
sfv= L/Lv
x = sfuu
y = sfv v

Answer 24

Calibration Formulae

Question 25

2 D Image faults

Answer 25

Camera placement/alignment error
Deformed image
Perspective error

Question 26

Mitigation of perspective error

Answer 26

move camera as far away as possible

Question 27

2 D analysis camera settings

Answer 27

sampling frequency
aperture setting
shutter speed
field of view

Question 28

Marker placement for 2D imaging

Answer 28

at approximate joint centers

Question 29

What system is used to determine position in biomechanics?

Answer 29

Cartesian Coordinate System

Question 30

Global Coordinate system

Answer 30

Defines position and translation of body in space

Question 31

Local Coordinate system

Answer 31

Set of x,y,z axes associated with each node in a model

Question 32

What do each of the letters represent?

Answer 32

A. Global Y axis
B. Global X axis
C. Local Y segment
D. Local Y Joint
E. Local X Joint
F. Local X segment

Question 33

How do you compute segment (absolute) angles

Answer 33

measured relative to a fixed reference

Question 34

how do you compute relative angles?

Answer 34

difference between segment angles

Question 35

Dot Product

Answer 35

Takes two equal length sequences of numbers and returns one

AB=|A||B|cos theta
theta = cos^-1 {(AB)/(|A||B|)}

Question 36

Steps to computing thigh angle

Answer 36

1. Create two vectors
   -right horizontal (a)
   -thigh vector (b) (subtract knee marker from hip marker)
2. Fight Lengths of A and B (pythagorean theorem)
3. divide each coordinate of the thigh vector by the length of the thigh vector to get unit vector
   4 multiply vectors and take the inverse cosine of the quantity
   theta = cos^-1(AxBx+AyBy)