Coordinaiton S2W5 Flashcards
definition of coordination (Oxford English Dictionary)
“The organisation of the different elements of a complex body or activity so as to enable them to work together effectively”
definition of coordination (van Emmerick et al. quoting Turvey, 1990)
“Coordination involves bringing together the degrees of freedom at each level (e.g. motor units, muscles, segment, joints) into proper relations”
initiating movement: pulling on desk
- leg muscles (gastrocnemius( switches on first to fixate the body - need solid base to pull against
- biceps can’t work effectively unless we coordinate the legs to create a stable base
anticipatory postural adjustments
- putting the body in a good position to be able to carry out the task
reaction time tests to look at anticipatory postural adjustments
Method:
- various reaction time tests whilst measuring EMG in muscles involved
Results
- we have a proximal to distal sequencing of the muscles switching on - due to transmission time of the signal but goes beyond this
- but when we don’t need to stabilise the joints (e.g. sensor we have to press and arm are resting on table), we don’t see the proximal to distal sequencing
angle during single joint movement
- joint angles changing follow an S-shaped curve
- initially not moving, then quick movement, then not moving again
velocity during single joint movement
- velocity is the speed of an object in a particular direction
- if starting still, initial velocity = 0, and velocity = 0 at the end, but speed up and slow down in the middle
- steepest part of curve = highest velocity
acceleration during single joint movement
- acceleration is the rate of change of velocity
- acceleration = force x mass
- force = mass x acceleration so forces we are producing will follow a similar pattern
- acceleration to speed arm up (+) and deceleration to slow the arm down (-)
agonist-antagonist patterning with elbow extension
- triceps (agonist) switch on to move the arm
- then biceps (antagonist) switch on to slow the arm down
- then some combination of the two at the end
- this is called a triphasic pattern of activity
- remember EMG patterns show when muscles switch on and how active they are - takes time to produce force
agonist-antagonist patterning when throwing a heavy medicine ball
- when throwing a light ball arm moves fast so would need lots of biceps activity to slow arm down
- medicine ball is heavy so arm moving slowly so only need small amount of biceps activity to slow arm down
(Chowdhary and Challis, 1999) study on release time: Method
- task: throw tents ball at 20cm target 8m away
- arm resting on table so can only extend elbow and wrist
- they created the simulation model which is a mathematical representation of two segments: mass and inertia, and a segment for the wrist
- at each joint had a torque generator
- can determine when to turn elbow on and off and same for wrist
- can look at timing required between those two events and when you need to release ball to still hit target
- carried out twice: 1. to determine fastest and most accurate throw and 2. to determine most robust to 4ms errors (still hits target despite not being timed perfectly)
- trying to determine optimum release time
(Chowdhary and Challis, 1999) study on release time: Results
- there was a 49ms delay from switching on elbow to switching on wrist (56ms when robust)
- release time 84.3ms (89.4ms when robust)
- release window - time where ball could have been released and still hit target = 1.2 ms (2.4 ms when robust)
- very small window to be successful
define robustness
measurement of tolerance to change in parameters
tapping study
Method
- a pressure sensor under each index finger
- 3 conditions:
- left and right simultaneous
- left then right (smallest time we can get between the two?)
- right then left
- 3 groups:
- control
- practice group
- instructed practice
Results
- when we think we’re touching sensors simultaneously there is a mean inter-tapping interval of 5ms
- left then right, best group managed just over 10ms
- right then left best score was 7ms
- can’t time movements very precisely
bimanual coordination
brain must simultaneously control multiple movements, such as when we use our two hands to perform a task
bimanual coordination task - 2 pens
- 2 pens on table, 1 close, 1 further away
- say go and pick up as fast as possible
- speed-accuracy trade off - if we have to move limb further it will take more time to pick the pen up
based on Fitt’s law:
- pen far away has largest index of difficulty
- pen far away should have largest movement time
- when you try to pick up both pens at the same time the closer hand slows down
- typically when the two arms are working together, they don’t have exactly the same movement pattern (pens may not be picked up at exactly the same time) but the time at which both hands reach their peak height is coordinated
explain how bimanual coordination can be an advantage
- motor equivalence - e.g. when writing forwards with dominant hand and mirroring with other hand, it makes writing with other hand easier due to bimanual coordination
- bimanual coordination makes some tasks easier so can be an advantage
explain how bimanual coordination can be a disadvantage
- e.g. moving foot clockwise and then with hand write number 6 in air
- foot then starts moving anti-clockwise
- easier to move them in the same way
- bimanual coordination is a disadvantage for some tasks when you want to move each limb independently e.g. drumming
define variability
“Every time we replicate the same movement, a certain amount of change may be recorded between its subsequent repetitions” (Preatoni et al., 2012)
variability - noise - writing name example
- if you write your name
- then put pen back on paper exactly where you started, and write name again
- do this 10 times
- there won’t be a single one that lies exactly on top of the others
- always going to be a small deviation as there is noise in the signals we produce in the motor system
two types of variability: 1) increasing the degrees of freedom
- beginner –> freeze the degrees of freedom to simplify it and control the movement with one joint
- expert –> unfreeze the joint = more variability in movement
two types of variability: 2) kinematic movement variations
- If we’ve got a certain technique we use and do lots of trials we find none of those trials look identical - always some variation which can be due to these things:
- there is always some noise from the motor system
- conscious feedback corrections
- planning error - sometimes our movements look different because we plan them slightly differently
