kin 216 class 12 quantitative analysis

Technical setup when analyzing human movement

1. High-speed cameras: capable of high resolution and capture rate (30-10000hz)

2. Camera placement: always 90 degree to the plane of motion or line up camera axis of rotation

3. No of cameras: 2+ cameras for 3D

4. A controlled env with good lighting

5. Reflective markers: attached to anatomical landmarks to represent joint centers and segments

6. Calibration object: of known length for scaling factor

7. Computer software: to digitize markers and compute kinematics

What movements occur in sagittal, frontal and transverse plane

Sagittal (Pitch): Mediolateral

Flexion and extension

Frontal (Roll): Anteroposterior

Ab/Adduction

Transverse (Yaw): Longitudinal

medial + lateral rotation

Steps to analyze human movement?

1. Collect temporal data: (when things happen)

   1. Use camera sampling rate to determine timing

   2. Identify frame number and time stamp

2. Establish spatial reference (where is body in space)

   1. Draw an X-Y coordinate system thru a fixed marker in each frame

   2. Use fixed reference or moving reference depending on goal

3. Calibrate using scaling factor (how big things are)

   1. Place an object of known length in the field of view

   2. Compute scaling factor:

      1. real world distance/measured distance

4. Digitize points:

   1. using computer software

What is time stamp?

The time interval between frames

e.g. if a camera has 15 Hz. each picture represents 1/15th of a second. so the time between each picture is 0.0667s.

to calculate movement time, multiply frame number by the time stamp or divide frame number by 15 (sampling rate)

e.g.

camera 15 Hz

when does frame 9 happen

1/15 = 0.0667.

9 x 0.0667 = ..... s

Scaling factor

Converts pixel distances → real world distances

Must include known-length calibration object that tays visible and unmoved

Formula:

SF = real distance / measured distance

What kind of variables can be measured?

temporal (looking at time), kinematic (position of body, how far you move) or kinetic (measure forces)

what makes quantitative analysis good

objectivity (free from bias)

reliability (same results every time)

validity (measuring the things you want to study)

Describe motion capture

Motion capture is the process of using video or picture cameras to gather images and study moving system

camera should always be

90 degrees to plane of motion and stationary

Aligned with the axis of rotation

analyzing movement can be with simple tools like ________ instead of expensive and time consuming motion analysis

camera, calculator, ruler

after calculating time, next we need to determine

position in space. require spatial reference system

spatial reference system can be

fixed or moving

fixed reference

describes movement relative to the environment or space

important when comparing different participants

moving reference

examines the movement of a body segment

example,

how can we measure scaling factor for a video of person running

have a meter stick in the video (1000mm). then measure the meter stick from the video (20 mm).

real value / video value = scaling factor = 50

now if we want to measure if the participant ran 60mm in the video, how much she ran in real life,

we calculate 60 x 50 = 3000 mm = 3 m

the last step is

digitization. representation of an object by a series of discrete points (markers),

markers indicate joint centre of rotation (instant centre) and position of skeletal landmarks

how to find displacement from a video

●Look for body pos in picture – measure how far from x and y axis. Determine body position.

●Change in position = difference btwn those two values, btwn one picture and the next.

how to find velocity from video

find displacement, then divide it by time between the two frames (sampling rate)

horizontal and vertical are separate. then can be combined to get resultant velocity of a particular joint of interest

can determine magnitude and direction since it is a vector

how to find acceleration from video

get velocity and divide by sampling rate

can get horizontal and vertical and combine for resultant acceleration

analyzing angular movements begins with

joining markers to form linear segments.

need at least 3 markers and 2 segments to find an angle

relative angle needs

3 markers and 2 segments

absolute angle needs

two markers and one segment and one line of reference

pressure pads

measure timing of perfomance

force plates

using transducers to measure forces involved in motion

electromyography

measure muscle activity during movement

who uses motion analysis

athletes, coaches, speech therapists, filmmakers, video game designers, clinical therapists,

Why are reflective markers placed on the body during motion capture analysis?

●A1: Reflective markers are placed on body during motion capture analysis to use as markers to track a specific body segment or joint.

Why is it important to use a fixed reference when analyzing human movement, particularly when comparing different participants?

●A2: Use fixed reference to analyze movement when you want to compare movement analysis between different participants.

What is a scaling factor, and why is it needed in motion analysis?

●A4: scaling factor  = real world distance/measured distance. A way for us to convert the measured distance in the captured picture into the real-world distance equivalent. Purpose of a  scaling factor is to know how ‘big’ things really are in real-life.