AMC Sem 2 Flashcards
Describe the double pendulum chaos theory
The dbl pendulum has high sensitivity to initial conditions
Low speed start - get stable inphase or anti phase
High speed start - behaves chaotically in an unstable state
What is a fractal
Infinitely complex pattern that is self similar across different scales
Describe dimensions of a fractal
Dimension is not equal to the space it resides in.
Eg Koch snowflake - length measured depends on the size on the measuring stick
Types of self similarity in fractals
Spatial self similarity- shape is repeated at arbitrarily smaller and smaller scales
Temporal self similarity- shape is repeated over time course eg graph has same pattern if over 3 min, over 30 min or over 300 min
Describe physiological fractal example
Lungs
Follow simple rule of go certain distance then divide in 2
Causes surface area to be much bigger than if a traditional geometric structure was followed
More efficient gas exchange
Impact of fatigue and age on self similarity
Likely to go from self similarity to brownian noise
Types of noise + their predictability
White noise - completely unpredictable
1/f noise (pink noise) - some predictability
Brownian noise - more predictable only small variations can occur at any time point
What is standard deviation
Measures how far individual data points are dispersed from the mean of that data set
Can measure magnitude of variation but takes no account of data order
Can’t identify self similar behaviour
What is coefficient of variation
Ratio of the standard deviation to the mean
Higher coefficient of variation = higher variation
Can measure magnitude of variation but takes no account of data order
Can’t identify self similar behaviours
What is entropy
Measure of level of uncertainty or disorder in a given data set
Higher entropy = more uncertainty
It increases as freedom of choice increases
Helps quantify signal regularity
Entropy values
0 = completely predictable
2 = white noise
What is detrended fluctuation analysis
Analyses statistical properties of time series data
Can detect self similarity
Separate data into boxes, make best fit of each box, calculate deviation of each box. Repeat with smaller and smaller boxes
What is plotted on detrended fluctuation analysis graph
Log of root mean square error vs Log of corresponding box size
Detrended fluctuation analysis alpha exponent values
0.5 = white noise
1 = pink noise
1.5 = brownian noise
Heart rate complexity analysis results
Compared young and old
Both had resting HR 65 but ApEn young 1.09 old 0.48
Young - more unpredictable- good as it means it responds better to environment + stressors
Why do we fluctuate
Interactions of lots of different signals
Motor unit recruitment
Motor unit firing
Muscle tendon interactions
Entropy in older and younger females strength based task
Lower SampEn and ApEn in older - decreased complexity
Strength training made no difference
Why get loss of complexity with aging
Denervation renervation process leads to larger, slower motor units
Older people have 20-40% fewer muscle fibres
Define fatigue
Process that can lead to exhaustion
Neuromuscular fatigue = loss in the capacity for delivering force + or velocity of a muscle resulting from muscle activity under load. This is reversible by rest
Define critical power
Maximum rate a muscle can keep up for a long period of time without fatigue
What happens when exercising above critical power threshold
Fatigue occurs, fixed energy reserve is used which determines exercise duration
What happens when exercising at or below critical power
Task is fatigueless
Energy reserves are not used up
What happens during sub maximal exercise (fatigue)
Compensation for fatigue is possible allowing task to be continued but at the expense of maximal force/power generation
Describe loss of complexity with age hypothesis
The down regulation of systems or less good integration reduces complexity of processes/outputs
Isometric force production variation
If told to hold a set force typically remain in right area with some slight fluctuations
Describe task failure experiment
Complete intermittent contractions until task failure
Perform MVC every 1 min
The fall in the MVC is a measure of fatigue
Describe central fatigue
Exercise induced processes reducing force proximal to NMJ - Brain/CNS/PNS effected
Describe peripheral fatigue
Exercise induced processes reducing force at or distal to NMJ
- muscle fatigue
Describe a superimposed twitch
Apply stimulus during contraction
If maximally activated the twitch shouldn’t increase output
Describe potentiated resting twitch
Stimulus is applied at rest - no input from CNS
Gives idea of muscle capacity
Peripheral fatigue results in reduced resting twitch
How to measure central fatigue
Voluntary activation = (1-a/b x 100)
a = superimposed twitch
b = resting twitch
How to assess central and peripheral fatigue
Use muscle stimulator
Can be per cutaneous or femoral nerve (better but less comfortable)
Effect of central fatigue on EMG
EMG is reduced
Submaximal EMG is increased to compensate for peripheral fatigue
Neuromuscular fatigue and critical torque
If above critical torque get progressive neuromuscular fatigue
Describe experiment re neuromuscular fatigue + critical torque
2 bouts exercise below torque + 2 bouts above torque
Below showed some progressive fatigue but able to continue for whole hour
Above - v significant fatigue, task failure within 15-20 min, had to use MVC to achieve desired force by the end
What is critical torque
Key fatigue threshold for peripheral fatigue
Does fatigue induced loss of complexity occur below the critical torque
No, metabolic rate cannot be stabilised above the CT therefore progressive reductions in torque complexity should only occur above CT
What is complexity driven by
Peripheral body eg muscles as no loss of complexity occurs below CT
Experiment to confirm complexity is driven by peripherals
- Exercise to task failure
- Group 1 allowed 3 min recovery, group 2 use cuff to occlude + prevent recovery
When no recovery occurs complexity remains low but complexity increases during recovery
Effect of caffeine on fatigue
Ingest either 6mg/kg caffeine or placebo
Caffeine prevented fall in neuromuscular complexity but no change in fatigue level
Suggests complexity plays a small but significant role in complexity
Define balance
Active control of physical shape of limbs to provide varying degrees of passive stability + muscular actions to provide compensatory active stability for passive insufficiencies
Define stability
Tendency for body to remain in or return to its initial position following application of force. Can be passive or dynamic
Why do we have postural sway
Impossible for body to remain completely still
- passive instability
- muscle errors
-sensory errors
-feedback delays
-control strategies
What happens in stable equilibrium
Likely to return to stable state following small perturbations
What happens in unstable equilibrium
Small perturbation cause centre of gravity to move more easily
4factors passive stability depends on
Weight - more mass = harder to accelerate/ be knocked
Area of base - more area = more stable
Horizontal distance of centre of gravity to pivot point
Height of centre of gravity above base - higher = less stable as the more of CoG moves for each 1 degree of movement
Why do humans have passive instability
Small base of support
High CoG above base
Describe dynamic stability in humans
Have passive instability so need active muscle contractions to maintain stability
Use muscles that cross joints to maintain or regain balance
CoG must remain in base of support
Describe muscle errors
Muscles cannot produce perfectly constant force due to variation/error or over/underwhelming force
Muscles act across multiple joints and in multiple planes/axis - need to use synergists or other muscles to control/stabilise other body parts
What proportion of sensory information does each part provide
Vision 10%
Vestibular apparatus 20%
Somatosensory proprioception (Golgi tendon organ/ muscle spindle etc) 70%
Why do we get sensory errors
Different inputs may cause sensory conflict (what makes you motion sick)
Require some movement to work
Describe sensory threshold
How much movement is needed for sensory system to say you have moved
Really slow movement can’t be detected
Really fast movement detected all the time
Proprioception has the lowest threshold
Vestibule highest threshold need to move quite quick, quite a lot to detect movement
Describe feedback delays
Input - delay- processing- delay output - delay - feedback
What is sensory delay
Time taken to detect movement
Varies based on movement- larger movement = smaller delay
Describe neurological delay
65-130ms
Afferent signal transmission - 50ms
Descion time - varies
Efferent signal transmission- 50ms
Describe electromechanical delay
13-55ms
Time taken from muscle activation til force is produced
List 5 control strategies
Ankle strategy
Hip strategy
Mixed strategy
Arm swing
Stepping
Describe ankle strategy
Sway about the ankle
Controls CoM via ankle torque
Most commonly used in quiet stance
Fixed hip angle
Bad on narrow surface, good with low friction
Describe hip strategy
Use when need to respond quickly
Uses more energy but requires less effort
Controls CoM by horizontal force
Hip angle is opposite to ankle angle
Good on narrow surface, bad with low friction
Describe mixed strategy
Uses hip and ankle together
Often done in practice as allows head to remain up so can still see
When are arm swing and stepping used
Arm swing - when can’t step eg in gymnastics
Stepping- to prevent falling
What is a control strategy tolerance reigon
Along where the CoG is in the same position in relation to the ground
Benefits of staying within control strategy tolerance reigon
Mechanically efficient
Easier to control
Uses less energy
Describe the control model
Expansion of information processing model from engineering
Involves model with assumptions- simplification of true system
Any variation = unwanted error
Add random error to try to simulate humans
Describe proportional (PID controller)
Present state of system (position)
Quick to correct but leads to overshoot
Describe integral (PID controller)
Past state of system (average over time)
Corrects for drift but is slow
Describe derivative (PID controller)
Future state of system (current velocity)
Prevents overshooting and is similar t dampening
Describe an example of PID controller
Peterka 2002 used numerous sensory perturbations to determine weights for sensory input - vision 10%, vestibular 20%, proprioception 70%
PID problems
Simulation output = too good - need to add error or would be perfectly still
Relies on excessive noise to reproduce typical postural sway
Struggles with latrge delays
Can use intermittent control models
Describe isolating 1 part of a non linear system
It changes the way the whole system evolves, and changes how components in the system are used
So may need to use an alternative method to assess the system in its entirety
Balance alternative approaches important bits
Variability is a fundamental part of the system not just unwanted noise
Movement is integral to perception
Sway magnitude is less important
Pattern of sway is more important
What is information entropy
Loss of information due to reduced order
Lower entropy = less loss of information ( easier to predict future)
Describe signals and information entropy
Periodic signal = low entropy
Complex signal = med - high entropy
Random signal = high entropy
What is the lyapunov exponent
Measure of local stability of a system
Low stability leads to exponential divergence in signal trajectories
Signals and lyapunov exponent
Periodic signals - high stability, zero divergence of trajectories
Complex signals - some instability, trajectories diverge as time progresses
What is used in non linear signal analysis
Entropy and Lyapunov exponent
Describe Harbourne + stergiou 2003 postural control in infants study
As child progresses from stage 1 (sitting with support) to stage 3 (independent sitting).
Lyapunov exponent decreases as become locally stable
Approximate entropy initially decreased and then increased slightly as baby began to explore
Describe Bardy et al 2002, 2007 experiment re control strategy and task frequency
Examined postural responses to tracking a moving target
Target frequency increased or decreased gradually
What is Newells constraints approach
Have task constraints, organism constraints and environmental constraints
Movement is the product of interaction between these constraints
What is motor learning in newells constraints approach
An ongoing dynamic process driven by constraints
It involves-
Search of perceptual motor landscape
Stabilisation and refinement of functional movement patterns
Optimisation of control by exploiting environmental and task information
Bardy et al 2002, 2007 results
Strategy used depended on task frequency
Hip strategy - anti phase coordination
Ankle strategy - in phase coordination
Different transaction points showed hysteresis in strategy selection
Are reigons of bistability where either strategy is acceptable
Pupil function
Dilated and constricts to let more or less light through
Cornea function
Protective barrier from foreign bodies and UV radiation
Initial refraction
Lens function
Uses refraction and accommodation to focus light on retina
Retina function
Cones - bright light , coloured central vision
Rods - dim light, peripheral vision
Optic nerve function
Transmits sensory info for vision to the brain in the form of electrical impulses
Describe binocular vision
Use both eyes together, the difference in the angle of light hitting each eye gives important proprioception information
Describe nasal + temporal
Nasal = nose side
Temporal = lateral side
Nasal fibres cross over at optic chiasm so info is on the same side
Name types of eye movement
Fixations
Saccades
Describe fixations
Central visual field (within 3 degrees)
100ms+ duration
Conscious processing
Describe saccades
Rapid eye movements
Between fixations
Information is suppressed.
Beneficial to work out where something will be + use 1 saccadic to move eyes there than to try + track it using multiple saccades
Describe focal vision
Aka ventral
Used for identification (what?)
Central visual field
Conscious- takes more time but gives more info
Describe ambient vision
Aka dorsal
Optical flow (Where something is)
Central and peripheral visual fields
Non-conscious - quicker
Describe pathways of vision
Optic nerve to occipital lobe
Dorsal = occipital lobe to parietal lobe to frontal lobe
Ventral = occipital lobe to temporal lobe to frontal lobe
Both frontal lobe (response planned) to pre-motor + motor cortex (sequenced and specific movement organised)
Describe optical flow
Closer objects appear bigger and take up more space on retina - size of something in visual field gives idea of how far away it is
Time to contact equation
Time to contact (Tau) = size of image/rate of expansion
How do we use vision in interceptive tasks
Use image direction on retina
Eg if both sides of a ball are on your left it will be on your left
If one side of ball is on either side, it will be hitting you.
The less the speed difference between the 2 sides = the wider it will pass
Calculation to intercept
Tau dot
Need to couple running speed with rate of change of tau
Stop just short - 0.5<tau dot <0
Hit whilst moving eg rugby tackle 1< tau dot <0.5
Interception accuracy
Typically slower = more accurate
BUT
Timing tasks have a reversal of speed accuracy trade off.
Easier to intercept at higher speeds as is easier to time
Describe cricket batting cue experiment
Compared high skilled and low skilled players
Occluded sight of ball at various points
Pre-bounce occlusion results similar to no occlusion control results
Pre-release occlusion results dropped to virtually 0 for low skilled but only 50% for high skilled.
Suggests high skilled players use pre-release cues
Describe cricket ball tracking experiment
Elite players tracked ball first 100-200ms, saccade to bounce, then tracked onto bat - allowed longer viewing before and after bounce
Low skilled tracked ball first 100-200ms but we’re unable to accurately predict bounce so struggled tracking ball to bat
Describe differences when batting v bowler/machine
Vs bowler - things that occur earlier in movement are greater
Vs machine -things that occur later in movement eg wrist flick are greater as don’t get visual cues from machine
