Biomechanical Measurement and Modelling

Question 1

How do we measure kinematics

Answer 1

-motion capture

Question 2

Characteristics of motion capture

Answer 2

-accuracy
-capture rate
-measure volume
-easy use

Question 3

Motion capture accuracy

Answer 3

-how accurately position can be estimated

Question 4

Motion capture rate

Answer 4

-number of still frames captured per unit time

Question 5

Motion capture measure volume

Answer 5

-volume of space in which marker position can be accurately determined

Question 6

Motion capture easy use

Answer 6

-fast to instrument

Question 7

Motion capture non-optical systems

Answer 7

-mechanical
-inertial
-magnetic

Question 8

Mechanical motion capture

Answer 8

-electronic goniometers/exoskeletons that sense joint angle
-inexpensive, unlimited capture volume
-cumbersome, few angles possible

Question 9

Inertial motion capture

Answer 9

-accelerometer and rate gyro signals to determine position
-untethered, unlimited capture volume
-accuracy not always great because of drift

Question 10

Magnetic motion capture

Answer 10

-sensors that detect position with respect to a source magnetic field
-no optical occulsion
-wires, complex

Question 11

Motion capture optical systems

Answer 11

-passive marker
-active marker
-markerless

Question 12

Passive marker motion capture

Answer 12

-light is reflected off markers and captured by cameras
-no wires required
-marker overlap and occlusion can happen

Question 13

Active marker motion capture

Answer 13

-LED markers emit light in a sequence capture by cameras
-no marker confusion
-wires required and occlusion

Question 14

Markerless motion capture

Answer 14

-automatically identify body landmarks from images
-no markers, no overlap or occlusion
-early stages

Question 15

How many cameras are needed for a 2D image

Answer 15

-1 camera

Question 16

How many cameras are needed for a 3D image

Answer 16

-2 or more cameras with appropriate calibration

Question 17

How do we measure kinetics?

Answer 17

-strain gauge
-force plates

Question 18

Strain gauge

Answer 18

-measures strain (change in length) under tension and compression

Question 19

How does a strain gauge work

Answer 19

-there is a wire inside that can increase (stretched wire) or decrease (compressed wire) resistance
-to estimate level of force you measure the voltage drop across strain gauge

Question 20

Force plates

Answer 20

-used to measure forces and torques under foot
-uses a network of strain gauges

Question 21

What measures do we get out of force plates

Answer 21

-3 forces: Fx, Fy, Fz
-3 torques: Mx, My, Mz

Question 22

How do we measure muscle activation

Answer 22

-electromyography

Question 23

Electromyography

Answer 23

-measures current generated by ionic flow across membrane of muscle fibres

Question 24

Types of EMG electrodes

Answer 24

-surface
-fine wire
-needle

Question 25

Sources of noise from EMG signal

Answer 25

-noise in electronics components in detection and recording equipment -ambient noise from sources of electromagnetic radiation (radio, TV etc) -soft tissue artifact -electric voltage from heart

Question 26

Forward dynamics

Answer 26

-measure: kinetics -calculate/estimate: kinematics

Question 27

Inverse dynamics

Answer 27

-measure: kinematics -calculate/estimate: kinetics

Question 28

System identification

Answer 28

-measure: kinematics and kinetics -calculate/estimate: inertial properties (mass, mass distribution)

Question 29

Reasons why foot length may change between frames

Answer 29

-soft tissue artifact -out of plane movement -body as a non-rigid object

Question 30

Soft tissue artifact

Answer 30

-the markers are sitting on the skin and fat -therefore the markers may move during movement

Question 31

Out of plane movement

Answer 31

-if you are recording in a 2D direction and are walking in a motion falling outside of the sagittal plane it would fall out of range and therefore the length of the foot would be changing

Question 32

Body as a non-rigid object

Answer 32

-foot length may change because there is different amount of stress being applied to the foot and it an be strained in different ways -the body is not a rigid object