BMEG 230 MT2

Question 1

3D tracking methods

Answer 1

Passive relective markers
Active Markers
Markerless

Question 2

Pros and Cons of Passive Reflective Markers

Answer 2

Pros:
* Accurate
* Capable of large frame rates
* Complex 3D motions
* No wires
Cons:
* Need multiple cameras
* Manual marker identification or need software
* Mis-identified markers
* Usually constrained to a lab setting, struggles
in uncontrolled lighting

Question 3

Pros and Cons of Active Marker

Answer 3

Pros:
* Accurate (especially in uncontrolled lighting)
* High resolution
* Greater capture volume
* Complex 3D motions
* No need to identify markers
* Less likely to loss sight of marker
Cons:
* Wires can be intrusive
* May need multiple cameras
* Complex to setup
* “bit of a pain” – Pawel

Question 4

Pros and Cons to Markerless tracking

Answer 4

Pros:
* Cheap and easy
* Unconstrained motion
* In the field data collection
* Can have various modalities of video
Cons:
* Not very accurate (yet)
* Mostly still in the research phase
* Usually need large training data sets
(i.e. machine learning)
* Can be constrained to single-plane and
simple motions
* Takes time/computing power to
process data

Question 5

What do force plates measure?

Answer 5

GRFs - Fx,Fy,Fz
CoP
momets of forces
impulse

Question 6

how do they measure this

Answer 6

• Convert energy from one form to another
• In our case: mechanical to electrical
• We cannot “measure” force, but we can measure strain as a
  change in electrical resistance

Question 7

Strain Gauge

Answer 7

• change their resistance as they are stretched or compressed
• to measure a desired change, there is a velocity drop acroos the strain gauge for a given level of force.
• uses differing sensors in different locations to determine CoP

Question 8

Pizoelectric in force plates

Answer 8

*Deformation to cause charge is very
small (usually a few microns)
* High frequency response
* Can not measure static loads
* Excellent for dynamic and impact loads

Question 9

CoP

Answer 9

All ground reaction forces
can be replaced by a single force acting
at a single point. This point is called
the center of pressure.

Question 10

how is voltage used to determine CoP in force plates

Answer 10

the force plates outputs the voltages proportional to forces, then coverted while accounting for amplifier gains and plate sensitivites. The forces are then used to calculate where the CoP is

Question 11

Degree of Freedom

Answer 11

an expression that describes the ability of an object to move in space.

Question 12

How many degrees of freedom are there for:
human finger
human shoulder

Answer 12

2
3

Question 13

why are degrees of freedom important

Answer 13

1. Understanding Movement: Knowing the degrees of freedom helps us understand how joints and bodily systems move and what
   limitations they may have.

2.Modeling and Simulation: In computational biomechanics, degrees of freedom are essential parameters for creating accurate
models of human movement.

3.Injury Prevention: By understanding the limitations of a joint’s degrees of freedom, healthcare professionals can better prescribe
treatments or preventative measures for potential injuries.

4.Prosthesis Design: Engineers use the concept to design more efficient and functional prosthetic limbs that mimic the natural degrees of freedom as closely as possible.

Question 14

Global vs Local coordinate system

Answer 14

• For global the rotation is performed concerning the global coordinate system whilst local concerns the local.
• in global, the axes of rotation are fixed and do not change as the object rotates, in local the axes is fixed to the object.
• A global Z-axis rotation means that no matter the current orientation of the object, the rotation will be around the fixed global Z-axis. In local it will rotate around its own z axis

.

Question 15

Definition of Inertia

Answer 15

the tendency of an object to maintain its state of rest or uniform motion, the resistance to change in motion of an object. The more mass the more inertia, the more resistance

Question 16

moment of inertia

Answer 16

depends not only on the masses, but also on how far they are from the axis of rotation

Question 17

Parallel axis theorem

Answer 17

if the mass moment of inertia about an axis passing through the center of gravity is known, the moment of inertia about a second, parallel axis is given by

I_pat = I_cg +M_t(R_cg)^2

I_cg = MOI about axis through cg
m_t = total mass of the object
R_cg = perpendicular distance between the axes

Question 18

Momentum

Answer 18

tendency to resist changes in the existing state of motion, only applies to moving ibjects, while inertia applies to moving and stationary

force is a change in momentum and time

p=mv
L=Iw

Question 19

impulse momentum principle

Answer 19

F * delta(t) = delta(p)

Question 20

Energy

Answer 20

kinetic = (1/2)mv^2
potential = mgh

Question 21

work energy principle

Answer 21

SUM(Fd)=(1/2)mv^2b-(1/2)mv^2a

Question 22

What is the instantaneous centre of zero velocity

Answer 22

when a body is moving there is a point where its velocity is zero for a moment, that point is not always attached to the body, seems to spin about that point

Question 23

how to find IC

Answer 23

velocity mag is proportional to relative distance, therefore we can use velocity being perp to relative distance. Draw lines perp to velocity, where they intersect is the IC.

v_a/r_a,ic = v_b/r_b,ic

Question 24

Instrumented Treadmills

Answer 24

• Force Platforms are built either into (AMTI) or under (Bertec) the treadmill
• Use strain gage platforms
• Measure Plate Forces and Moments (Center of Pressure and Free Moment computed
  from output)

Question 24

types of force plates

Answer 24

Strain Gage: * AMTI * Bertec * Kyowa-Dengyo Piezo-Electric: * Kistler

Question 25

Standing Balance Control

Answer 25

1. Muscle Stretch Reflex - Role in balance - Muscle tension adjustment 2.Vestibular System - Location and function - Orientation in space 3. Proprioceptive Feedback - Sources (muscles, tendons, joints) - Role in balance and posture 4.Teleceptive Inputs - Vision - Vision in spatial navigation - Environmental perception

Question 26

Kinetic energy equation for rotation

Answer 26

E = (1/2)mv^2 + (1/2)Iw^2

Question 27

rigid body force equations

Answer 27

F = ma sum(Fx) = ma_x sum(Fy) = ma_y sum(Fn) = (w^2r)m sum(Ft) = (alphar)m

Question 28

angular momentum about the COM

Answer 28

sum(M)=I(alpha)

Question 29

a body's trajectory can be determined if

Answer 29

the applied forces and moments are known

Question 30

if the moments is taken about a point different to COM

Answer 30

apply parallel axis theorem (I//) to determine the new I

Question 31

If COM is accelerating

Answer 31

sum(M_newpoint) = I//alpha +m(R_new/com x a_com)

Question 32

Definition of Dynamics

Answer 32

the study of how forces affect motion

Question 33

Definition of Kinematics

Answer 33

the study of motion in isolation

Question 34

2D planar video adavntages and disadvantages

Answer 34

Pros: * Cheap and easy * Various speeds * Can see the video after Cons: * Only in one plane * Can take a long time to process data * Hard to align properly and distortion correction is often required

Question 35

Distance Callibration

Answer 35

s = actual length / digitized length

Question 36

frame rate

Answer 36

- Fast Movements (e.g., running, jumping): Use a high frame rate, typically 120 fps or higher. This ensures fine-grained detail, reducing motion blur - Slower Movements (e.g., walking, stretching): A lower frame rate like 60 fps may suffice, but higher frame rates provide more detailed data

Question 37

Data triangulation

Answer 37

Enhanced Accuracy and Validation Minimization of Occlusion and Blind Spots Improved Depth of Analysis through Multidimensional Data Enhanced Reliability and Reproducibility Broader Context and Environmental Factors Reduction of Measurement Bias and Artifacts

Question 38

2D marker placement

Answer 38

3 DOFs X, Y of the COM and one angle describing its orientation

Question 39

3D marker placement

Answer 39

6 DOFs X, Y, Z of COM and 3 angles describing its orientation

Question 40

equations for attached bodies

Answer 40

R_b = R_a + R_b/a V_b = V_a + W_ab x R_b/a A_b = A_a + alpha_ab x R_b/a - W^2*R_b/a

Question 41

unit vector

Question 42

Acceleration

Answer 42

A_b = A_a + A_b/a A_b = A_a + (A_b/a)t + (A_b/a)n

Question 43

when would V_a = 0

Answer 43

when there is rolling without slipping