Kinematics Flashcards
What is biomechanics?
The study of the mechanical laws or principles relating to movement or structure of living organisms.
Provides conceptual and mathematical tools necessary for kinesiology professionals to improve performance or reduce injury risk.
Vectors
- have a magnitude and a direction
- vertical/horizontal components (relative to the ground)
- anatomical planes
- along a segment and perpendicular to it
What is a QUANtitate analysis?
Analysis of measurement of movement
- Involves quantification of movement
- Measurement (motion capture, forces, muscle activity)
- Modeling and simulation
- Common in research (becoming common in practice)
e.g. mathematical, SD, mean, linear regression
Advantages to QUANtitative analysis
- Accurate measurements
- Required for research
- Numerical comparisons
- Between individuals
- Across time
- across skill levels
- Databasing
- Allows data visualisation
Disadvantages of QUANtitative analysis
- Expensive
- Steep learning curve
- No single skill set
- Many different systems
- Difficult to summaries data
- Time consuming
- Lacks ecological validity
- Isolated skill
- Lab-based
Biofeedback
Giving them information instantly about them while they are doing the activity e.g. 80degree threshold and learn where it is once we hit it (during the movement)
What is QUALitative analysis?
Visual analysis of the form of the movement
- Judgment of the quality of the movement
- Based on observation (video)
- Can involve qualitative analysis of video or of quantitative data
- Structured approach and knowledge of mechanics are important
Should be done in natural environment whenever possible
e.g. video, case study, analysis, theories
Advantages of QUALitative analysis
- Can be done in natural setting
- Inexpensive, faster, convenient
- Less technical skill needed
- Can be more intuitive
- Coach and client friendly
Disadvantages of QUALitative analysis
- Observer bias
- Appearance of being easy to do and unsophisticated
- Findings aren’t quantified
- Reliability often overlooked (how consistent is set up)
- Appears to be easy and unsophisticated
QUALitative analysis approach
- Preparation stage - client needs, understand movement, build model
- Observation stage - Reviewing video, considering location and number of observations
- Evaluation and Diagnosis stage - strengths/weakness, validity/reliability, decide how intervene
- Intervention - feedback, review analysis in context of needs analysis
3 components of exposure
- Aperture
- Shutter
- ISO
Aperture
‘whole that lets the light in’
Size of opening in lens, larger allows more light but reduces depth of field
Shutter
Opens and closes to expose sensor to light
Slower shutter, more light (can cause motion blur)
Fast movements need fast shutter (and lots of light)
ISO
Sensitivity to light
increasing dark image = grainy
best image quality at low ISO levels, but need lots of light
perspective error
- plane of motion (camera perpendicular to plane)
- out of plane movement is a problem
- wide lens makes nearer objects larger and ones that arent centred distorted
- position camera far away, zoom in using telephoto lens, focus, zoom out so size of performer is maximised
*effects quality of analysis
Video calibration
allows a motion capture system to determine the position and orientation of its cameras relative to each other
- needed to make linear adjustments
- must be known size and in plane of motion
- relates pixels to real world units
- ruined by camera movement
What four factors influence the amount of available light when video recording a sports movement?
- Shutter speed
- ISO
- Apeture
- Frame rate ( frames per second)
What are two reasons that the accurate identification of anatomical landmarks is important?
Validity: accurately reflect the true position and movement of the anatomical structures being studied
Reliability: consistent and repeatable measurements across different studies
Generally, in empirical science what are the dependent variables?
Variables measured by the researcher to address a hypothesis.
What is the purpose of a calibration tool?
Allows for the video coordinates to be converted to the real world scale. That is, a conversion factor (e.g., pixels to meters) is generated.
What is the purpose of biomechanical measurement?
to answer a question about the performers movement.
- to modify an aspect of tecnique to improve performance
- gain further understandig of how the movement is performed (generally or under certian conditions e.g. post injury/surgery)
- modify movement to reduce risk of injury (or decrease pain)
Force plate applications
- Landing/take off forces
- force - time trace
- peak, mean forces , loading rates
- joint loads
- inverse dynamics using forces and kinematics
force plates
- strain guages detect changes in electrical resistance
- volts (V) converted to newtons (N)
- output 3D forces and touques, 2D centre of pressure
Internal measurment units (IMUs) ‘Sensor systems’
Accelerometer: Linear motion/kinematics, velocity from displacement
Gyroscope: Rotational velocity, displacements and accelerations
Magnetometer: Polarity of earth to figure out where you are heading
Accelerometer
IMU
- detect static (gravity) and dynamic (movement) forces
- can measure linear kinematics
Gyroscope
IMU
- detect rate of angular motion
- can measure angular kinematics
- 3 sensors
Magnetometer
IMU
- detects heading according to magnetic south/north
- can orientate acceleration and gyro readings
Kinematic quantities
- Position
- Distance and displacement
- Rate of change
- Speed and velocity
- acceleration
Position
- need a reference frame
- vector (written in bold)
- Symbol: S (bold)
What is a coordinate system?
allows us to determine an objects position
- usually one axis per measurement dimension
- E.g. looking at COM at take off (x 0, y 0)
Then looking at COM during trick (x1, y1)
Absolute (global) reference frames
- describe a landmark e.g. COM or segment positions
- Describe segment angles
- Describe relative to the world e.g. floor, gravity
example: orientation changes (e.g. flipping or driving car) when doing a flip (absolute/segment frame is not relevant)
Therefore relative is better (orientation of one segment, relative to another)
Relative reference frames
determines relative segment position e.g. stance width and joint angles
- Describes limb orientation relative to another
- Angles normalize body size and absolute location
Coordinate system orinetation
X-axis: mediolateral
Y-axis: anterioposterio
Z-axis: longnitudal
+ve directions: right, anterior, up
-ve directions: left, posterior, down
Position (s)
-where relative to origin
-need reference frame
-Vector (written in bold)
Distance (d)
Length of path
*no direction reference
- scalar (d)
Displacement (bold d)
Change in position (final - initial)
*has a reference to direction
Rate of change
Slop of graph = Y rate of change in relation to X
X: time
Y: e.g. displacement
Displacement / time = velocity
If slope - it’s the average (rate of change)
Speed
Rate of change of distance
*no direction - how fast
distance / time = s
Velocity
Rate of change in position
distance / time = v
Scalar
no direction indicated
e.g. Distance, speed, position, acceleration
- Measure of magnitude (how big, fast, long or wide)
- Measure of a scale of some sort
Distance (sum of all movements in whatever direction)
Vector
Direction indicated
e.g. Displacement, velocity
*when direction, position and acceleration also
- Magnitude and direction (north, 22 degrees, left/right)
- Need to provide more than just the scale or magnitude of the quantity
Displacement (end result of a movement, magnitude and direction)
What factors affect the path of a projectile motion?
Factors effecting projectile
- Angle
- velocity Vector: horizontal (Vx) & vertical (Vy) component
- Vertical (Vy) decreases at the rate of 9.81m/s every second during flight phase
- Vertical (Vy) determines the change in height and flight time
- Horizontal (x2) is constant and is needed to determine range
- Height: affects range of projection
- To increase range, lower launch angle with +ve projection height
- Higher launch angle with -ve projection height (bottom)
What is the importance of projectile motion?
- To understand the flight phase in sport, CoM follows projectile motion
- Optimizing / predicating flight
E.g. running, shooting ball
- Optimizing / predicating flight
Average velocity
Between two time points
Instantaneous velocity
calculated over a small (close to 0) time period.
Projectile motion
Projection speed
Projection angle
What is gait anaysis?
Analysing body segments through space and time during locomotion
Walking: monitor rehab, detect motor (dys)function, evaluate equipment
Running: avoid potential injury, improve comfort and performance, evaluate equipment
Phase division of gait
One gait cycle, stance phase, swing phase, double stance (walk) / flight phase (run)
One gait cycle
ground contact to next ground contact of same foot
stance phase
ground contact -> to off
1. Ground strike (initial heel contact)
2. foot flat (Foot eversion/pronation)
3. mid-stance (Foot under pelvis, end of loading response, propulsion begin)
4. heel off (Knee flexion with toe extension)
5. Toe off (foot leave ground)
swing phase
toe off -> ground contact
1. Early swing (hip & knee flexion) - 40 deg to allow ground clearance
2. Mid-swing (foot swing under pelvis, max knee flexion, hip still flexing)
3. Late-swing (knee extending, hip stops flexing and rotates laterally)
double stance
both feet on ground (walking)
*interchanged with flight phase when running
flight phase
no feet on ground (running)
*interchanged with double stance when walking
Differences between walking and running
- balance more important in running - no double stance
- greater vertical displacement - flight phase
- muscles must generate and absorb more energy
- greater hip extension before ground strike, knee extended at toe off (40 deg)
Spacial paramaters (gait cycle)
- STEP length (distance between consecutive ground strikes - between feet)
- STRIDE length ( distance between consecutive ground strikes of SAME LEG)
- foot angle (foot orientation in long axis relative to line of progression. influences amount of pronation & windlass mechanism)
- base (step) width (between ground strikes - heel, of each foot. can increase with motor impairment
Windlass mechanism
describes how the heel supports the foot during weight- bearing activities and provides information regarding the biomechanical stresses placed on the plantar fascia (heel)
Temporal paramaters (gait cycle)
- step/stride time: time between ground strikes
- single or double suppourt time: time body is suppourted by one or two legs
- swing or flight time: time one or two legs not in contact with ground
- stride frequency: stides per second
Hierarchal model of running
running speed -> stride length and stride time
stride time -> time of stance and time of flight
What determines running and walking velocity?
Stride LENGTH and stride RATE
V = Rate of change in position
distance / time = v
*relationship is not linear at higher velocities. At high velocities, increasing stride rate more than stride length.
stride
one locomotor cycle and is usually defined from one foot contact until the
subsequent contact of the SAME foot.
Stride length
The distance between consecutive steps of the same foot.
Step length
The distance between consecutive steps, which can expose left-right
asymmetry
Stride frequency
Number of strides per unit of time (typically seconds).
Joint angles
Angle between proximal and distal segment in the relevant plane of
motion.
What is the formula provided by Cavanagh and Kram (1989) for calculating stride length during treadmill running?
SL = 2sTV
Where;
SL = Stride length
sT = Step time
V = Treadmill velocity
Frequency
Inverted pendulum model of walking
stance limb - is the inverted pendulum
swing limb - is double pendulum
*both pinned at hip
Froude number
standardizing walking speed according to body size
V^2 / gravity (9.81) x leg length
*when greater than 1 (>), suppourt limb comes off ground
Angular motion in human movement
muscles contract creating joint tourques / moments and cause segment rotation
Linear movement can only be achieved through multi-joint coordination
e.g. :
-Com following a path = linear (even tho not straight line)
-Can be no linear movement without having angular movement
e.g. moving hand in straight line, coordinating shoulder and elbow and wrist rotation
Radian
SI unit for angle
the degree created when moved from perimeter of radius around the perimeter the length of the radius (arc length)
1 radius
- 2 radiuns in a circle (360 deg)
Radiuns = degrees / pi / 180
degrees = radiuns x (pi / 180)
Pi (3.141592)
The ratio of a circles circumference to it’s diameter.
(diameter is radius x2)
1 pi = 180 degrees
2 pi = 360 degrees
Radians and arc length
The longer the radius, the greater the arc length
- arc length = change in angle (radiuns) x radius
*coversion of deg to radians
(pi radians / 180 )
Muscle insertions close to joints
Short change in muscle length, produces a larger movement at the end limb
sports with implements
increase speed of object by increasing radius
- all have same angular velocity BUT linear speeds at the end of segment are faster (and go through larger distance)
Angular velocity and linear speed
Angular velocity can produce linear velocity at the END OF THE LIMB
What plane does the knee move in
during gait (flexion/extension)?
Sagittal plane (0-70deg)
What is Kinematics?
The study of motion (patterns)
Kinematic variables describe the motion of the object / system
