8. Biomechanical Analysis

Question 1

What is Analysis?

Answer 1

Analysis involves breaking something into smaller parts and then examining those parts

Question 2

What is Quantitative biomechanical analysis?

Answer 2

● If human movement or any of its aspects is described with numbers, the resulting analysis is quantitative

● Quantitative biomechanical analysis of human movement involves actual measurements of human movement and the underlying causes of movement

● Quantitative biomechanical analysis is often performed by coaches at the elite or professional level, by ergonomists looking at workplace safety issues, or by clinicians working with patients

Question 3

Pros and Cons of Laboratory Data Collection:

Answer 3

Pros
Carefully controlled environment
Predictable environment
Easy to study the skill in question

Cons
Not a real-world setting
Novel environment
Equipment may intimidate performer

Question 4

Pros and Cons of In-the-Field Data Collection:

Answer 4

Pros
Measure skills during competition
Athlete is minimally affected

Cons
Measurement tools not very portable
Restricted to non-invasive techniques
Environment is constantly changing

Question 5

What things do you need to be concerned with when measuring perfomance?

Answer 5

1. As objective as possible, eliminate bias
2. Relaibility, Repeatable Results
3. Validity, measure things you want to test

Question 6

Video provides limited quantitative data
Need the ability to look at individual frames

What type of camera should be used for analysis?

Answer 6

The camera must generate pictures with a lot detail (resolution)
The camera must be able to to take multiple pictures every second (capture rate)

Human eyes (24 Hz)
Commercial Cameras (30 Hz)
High speed cameras (500 to 10,000 Hz)

Question 7

What is Motion Capture?

Answer 7

Motion capture is the process of using video or picture cameras to gather images and study a moving system (and its constituent parts)

Question 8

What are Reflective markers?

Answer 8

Reflective markers are fixed to the body and indicate segment or joint position

Question 9

What is the best perspective for a camera for analysis. (3)

Answer 9

The camera should always be:

• 90° to plane of motion
• Placed on a tripod (camera not moving)
• Far enough away to capture the entire movement but close enough to see the body

Question 10

Answer 10

Camera needs to be alligned with the axis of rotation.

Saggital Plane: Medial-Lateral Axis
Frontal Plane: Anterior-Posterior Axis
Horizontal Plane: Superior-Inferior Axis (longitudinal)

Question 11

How do we record three-dimensional actions.?

Answer 11

One camera will record two-dimensional or planar motion.

2+ cameras are used to record three-dimensional actions.

Question 12

Why do Performers often wear spandex suits?

Answer 12

Performers often wear spandex suits or tight fitted clothing. Reflective markers attached to the suit will move as the limb or body segments move (so that the markers do not sway with clothing movement)

Question 13

What is the importance of Lighting?

Answer 13

High speed analysis requires good lighting for clear pictures (if you can’t see the markers, you lose data points). Light sources or sun blockers are helpful

Question 14

What do we need to know to Analyze Movement? (4)

Answer 14

First, we need to know when things happened in time

Next, we need to determine the positions of the body in space

Next, we need to know how “big” things are in the picture

Lastly, the performer is turned into a digital image

Question 15

On sheet paper

The video camera sampled the data at 15 Hz

• 15 pictures were taken every second
• Each picture represents 1/15th of a second

What is the time stamp?

Answer 15

The time stamp is the time interval between pictures

• The time between each picture is 0.0667 s

To calculate movement time:

• Multiply the frame number by the time stamp (0.0667)
• OR divide your frame number by 15 (sampling rate)

Question 16

How do we determine the positions of the body in space?

Answer 16

Fixed Reference
Describes the movement relative to the environment or space

Moving Reference
Examines the movement of a body segment

Question 17

How do we determine how “big” things are in the picture?

Answer 17

We need to convert distances in the pictures to real world distances - Conversion ratio or scaling factor

You need to place an object of known length in the picture

• The object must not move between frames
• The object should be clearly visible to the camera

This process is known as calibration

• Finding a relationship between two variables

Question 18

Calculating Scalar Factor

Answer 18

Scaling factor = 1000nm / 22 nm

unitless

Question 19

What is Digitization?

Answer 19

Digitization is the representation of an object by a series of discrete points (markers)

● Markers are typically placed on the body before the pictures are taken
● Markers are used to indicate the joint center of rotation
● Markers can reflect the position of skeletal landmarks