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What is 3D reconstruction?
The reconstruction of three dimensional coordinates of the images is usually achieved through the use of an algorithm.
What is the most POPULAR method for 3D reconstruction?
Direct Linear Transformation (DLT)
What does DLT require knowledge of?
- DLT requires knowledge of the x, y, z coordinates of known points in the field of view.
- This is provided by a calibration object (frame).
What is a limititation of DLT?
DLT coordinate reconstruction can only be guaranteed within the calibration volume.
What is important when setting up equipment? (reference frame)
You must ensure to know the distances between the points
Make sure the reference frame is level and the poles are aligned
What point is best in SIMI to set the point of origin?
What are the four things to set on a camera?
- Manual focus (not auto-focus)
- Shutter speed – the faster the better (reduces blurring) although the image will be darker.
- F-ratio – controls the amount of light entering the camera iris. Remember a low ƒ stop means a narrow range of focus.
- White balance – you can use automatic but it’s best to be certain by choosing either the indoor or outdoor setting.
What is filtering?
Filtering is the extraction of certain components of the signal, i.e. the noise.
What are the most common low-pass filters?
Why are butterworth filters low-pass?
- The highest frequency of the movement is entered into the computer program, which then removes all frequencies higher than the chosen frequency (which is why they are called low-pass).
- As a result, only the low (and presumably human movement) frequencies are left for analysis.
How are smooth curves calculated?
- Splines use complicated mathematical equations to calculate a smooth curve.
- We use cross-validated quintic splines.
What did Dempster do in 1955?
Dempster (1955) was one of the first studies to measure body segment parameters. He measured the dimensions of eight male Caucasian cadavers (age 52 – 83).
What did Hanavan do in 1964?
Hanavan (1964) used this data to create geometric modelling of the body (although his model does not include hands).
What did Clauser do in 1969?
Clauser (1969) followed Dempster’s procedures on 13 male Caucasian cadavers (age 24 – 78). He added in some new points.
What did Gubitz do in 1978?
Gubitz (1978) also used Dempster’s data but Gubitz omitted the feet and hands, while de Leva (1996) used Zatsiorsky’s gamma ray data on men and women.
What frames do you not use in analysis?
Don’t use the first or last 5 frames in analysis!
When must the resultant value be found?
Steps are rarely unidirectional so the resultant must be found.
How do you calculate cadence?
calculate cadence: velocity is divided by step length.
adding the step time to the flight time.
How do you calculate the distance of the centre of mass in front of or behind the supporting foot?
The distance of the centre of mass either in front of or behind the supporting foot is measured using the difference in their x-coordinates.
Why can't SIMI give any kinetic values?
It requires a force plate to.
Suggest 8 possible errors in reference to kinematics (motion anaylisis)?
- Equipment selection – 2 Canon DM-XL1 camcorders
- Camera positioning – adjusted for the race / course
- Camera synchronisation – manually after the event
- Calibration – possible to get all markers the correct distance apart?
- Performer preparation – must wear competitive clothing
- Skin markers – not possible
- Frame rate – 50 fields per second
- Digitising errors – possible to find joint centres accurately?
What is kinematics?
Kinematics is the branch of classical mechanics that describes the motion of points, bodies (objects) and systems of bodies (groups of objects) without consideration of the forces that cause it
Who discovered the Three Laws of Motion?
Who discovered Forces and the biological system?
Who attempted to measure GRF?
1872, 1873 Carlet, Marey.
Discovery of the piezoelectric effect?
Who made the First commercial gauge?
Who created the first commercial piezoelectric force plate?
Who invented the first commercial strain gauge force plate?
Who invented pressure distribution devices?
Nicol & Henning, 1976
MAREY’S FORCE PLATE (1882) was made from what?
9 sensors of rubber tube spirals leading to recording lever drum
MAREY’S RECORD OF VERTICAL JUMP
What is the pricipal of force tranducers?
An external force causes a strain within the transducer which sequentially generates an electrical signal proportional to the external force.
What are the 3 types of Force tranducers?
- Strain gauge
- Conductive piezoelectric transducers
What are other uses for force tranducers?
- Automobile engineering
- Aircraft engineering and rocketry
- Material testing
What are Strain gauge platforms made of, suited for and sensitive to?
- Strain gauge platforms are made of a material whose resistance changes with applied strain.
- They are mostly suited to static recordings (e.g. in standing posture control).
- They are sensitive to temperature changes.
What is the most popular Strain gauge brand?
The most popular make is AMTI.
What do Piezoelectric platforms rely on, and what is their weakness?
Piezoelectric platforms rely on the development of an electrical charge on certain crystals (such as quartz) when subjected to an applied force.
Their weakness is that they suffer from drift.
What is the most popular type of Piezoelectric platforms?
Kistler are the most famous type.
What are the 7 experimental proceducers setting up a transducer (force plate)?
- • Amplifier preparation (warm-up time).
- • Calibration (periodic calibration needed).
- • Set Sampling rate (sampling theorem*). Recommended rates: 500 Hz – 1000 Hz.
- • Set range / sensitivity.
- • Record subject’s weight.
- • Set collection time.
- • Ensure segment contact with the platform.
What should the sampling rate be set to?
What are the 7 measured variables of force platforms?
- Ground reaction forces (3 components) and resultant GRF
- • CG (centre of gravity) acceleration (F = ma)
- • CG velocity, displacement, momentum, angular momentum (integration)
- • Work, Power
- • Centre of Pressure
- • Moment of the GRFs
- • Friction
What are useful applications of force plates in biomechanics?
- Biomechanics of walking (gait analysis) and running
- • Biomechanics of other sports e.g. Long jump, high jump, gymnastics, cricket.
- • Biomechanics of injury
- • Evaluation and construction of different surfaces and shoes.
What is Impulse (momentum)?
How would you find the resultant of all 3 vectors?
How do you normalize the data?
- Subject’s body weight = 805 N;
- Force / 805 = Bodyweights
How do we find the net acceleration of the centre of mass from the force trace?
- 1. First need to remove the effect of acceleration due to gravity (weight) to find net forc
- 2. Next, we use the equation F = ma to find the net acceleration of the centre of mass
- 3. Use the centre of mass velocity to calculate both impulse (Impulse = mass x velocity) and power (Power = force x velocity).
What are the force accelerations?
DIRECTION OF GRF COMPONENT
- -------> Direction of motion
PERFORMANCE VARIABLES of CMJ
- • Impulse (y)
- • Take-off velocity (y)
- • Power (y)
- • Height of the jump (CG)
What are the further CMJ calculations?
What are determining factors to Increase Impulse in CMJ?
- • By increasing the size of the force
- • By increasing the duration of the force
- • By increasing both
- • How? (practical implications)
How to increase Impulse? (practical implications
- • Improve strength/power of hip, knee and ankle extensor muscles
- • Types of training
- • Exercise selection
What is this a graph of?
Standing long jump
What are the determining factors of long jump?
Generation of large impulses (x,y) in order to achieve high take-off velocities (x,y) and consequently great range (R=v2sin2θ/g
What are the practical implications of long jump?
- • Improve leg strength/power
- • Improve arm strength/power
- • Segmental coordination (technique)
What is this a graph of?
What are the determining factors of a somersault?
- • Avoidance of excessive braking impulses during landing
- • Generation of large impulses (especially y) in order to achieve high take-off velocities (x,y) and consequently adequate clearance to perform the rotation
What are the practical implications of a somersault?
- • Improve leg and arm strength/power (eccentric-concentric)
- • Segmental coordination (technique)
- • Velocity (integration) → Displacement
- • Force × Velocity → Power
- • Force × Displacement → Work
- Net Impulse graph(FR- FW) * t
- after working out the area
GENERATION OF THE EMG SIGNAL: MUSCLE LEVEL
GENERATION OF THE EMG SIGNAL: OVERVIEW
FACTORS AFFECTING THE EMG SIGNAL: OVERVIEW
What are the CAUSATIVE INTRINSIC FACTOR - Physiological?
- • the number of active motor units
- • the firing rates of the motor units
- • the fibre type composition of the muscle
- • blood flow in the muscle
What are the CAUSATIVE INTRINSIC FACTOR - Anatomical?
- • fibre diameter
- • depth and location of the active fibres
- • the amount of tissue between the surface of the muscle and the electrodes
What are the CAUSATIVE EXTRINSIC FACTOR?
- • Electrode types: surface and indwelling
- • Surface Electrodes: active and passive
CAUSATIVE EXTRINSIC FACTOR...continued?
- Placement of Electrodes
- • Location: over the mid-point of the muscle belly (not on or near the tendon; not on the motor end-plate; not at the outside edges of the muscle/cross-talk)
- .• Orientation: the line between the two electrodes should be parallel to the direction of the muscle fibres
- • Inter-electrode distance: 1-2 cm (up to 5 cm?).
- • Reference electrode: over an inactive/unrelated site.
- • Skin preparation.
CAUSATIVE EXTRINSIC FACTOR...continued?
- • Cross-talk: signal/noise from neighbouring muscles (left figure)
- .• Inter-electrode distance: the effects of inter-electrode distance on EMG amplitude (right figure: the distance between each electrode is 10mm)
What are sources of noise?
- • Inherent noise within the detection/recording equipment
- • Ambient noise (50 or 60 Hz)
- • Motion artifacts (0-10 Hz)
- • Background noise: it has to be estimated in order to determine the ON-OFF times of the muscle activation
What are possible solutions of noise?
- • Careful taping should be performed.
- • High quality shielded cables (reduction of movement artifacts: 0-10 Hz).
- • Use of pre-amplifiers.
- • High quality electronic components.
- • Bipolar configuration – differential amplifier (bandpass filters/elimination of ambient noise).
- • Computer processing: further filtering (example: adjacent graph).Uncontrolled Filtering
- • Tissues: low-pass filter.
- • Electrode to electrolyte interface: high pass filter.
- • Muscle Length: The amplitude and the frequency decline as muscle length increases
What cables should be used in EMG?
- • High quality shielded cables (reduction of movement artifacts: 0-10 Hz)
- • Use of pre-amplifiers (reduction of movement artifacts)
In EMG what level should sampling be at?
What are the 4 characteristics for amplifiers in EMG?
- • Gain: the ratio of the amplifier output voltage to its input voltage. The gain should be high:100-10000.
- • Input Impedance: this should be high so the input signal is not attenuated (recommended value: 100 times the impedance to the source electrodes)
- • Frequency Response: reproducibility of the original physiological signal by including all the original frequencies (10-1000 Hz)
- • Common Mode Rejection:the CMRR (common mode rejection ratio) should ≥10000 in order to reduce substantially the ambient nois
What is AREMG?
average rectified value over a time period (affected by both intrinsic and extrinsic factors).
What is RMS?
the square root of the average power of the signal in a given time (provides a measure of the number of recruited motor units).
What is IEM?
the area under the rectified EMG signal.
What is normalisation in relation to EMG?
Normalisation: Expression of muscle activity in relative terms.
What is MVC?
Reference values: Maximum voluntary contraction (MVC); peak/mean EMG from the same task
What are the advantages and disadvantages of MVC normalisation?
- Advantages: allows comparisons with other muscles, other subjects and between studies.
- Disadvantages: eliciting an MVC, repeatability, mechanics of movement
WHAT IS FREQUENCY-DOMAIN ANALYSIS?
- • Analysis of the frequency spectrum of the raw EMG signal
- • Parameters mainly used: mean and median frequency
- • Frequency analysis provides information in terms of muscle fatigue.
- • The examination of the power spectrum during sustained contractions can reveal the onset of muscle fatigue.
- • A noticeable shift in the power spectrum towards lower frequencies as shown by a reduction in the median and mean frequencies indicates the onset of fatigue.
WHAT IS THE TIME-DOMAIN ANALYSIS?
- • Full-wave rectification and then…
- • AREMG: average rectified value over a time period (affected by both intrinsic and extrinsic factors).
- • RMS: the square root of the average power of the signal in a given time (provides a measure of the number of recruited motor units).
- • IEMG: the area under the rectified EMG signal