Human Movement variability

Question 1

Define Motor skill:

Provide an example of a motor skill study

Answer 1

“The ability to bring about some end result with maximum certainty and minimum outlay(cost) of energy” (Schmidt)
- Best performance is the greatest likelihood of the outcome being successful
- Nikolai Bernstein, 1930 studied blacksmiths(career in hitting a nail with a hammer. People were able to hit the hammer on the nail every time(with a different path each time) - execution(the trajectory of the joint angles and the hammer), determines the result

Question 2

What are the causes of variability?

Answer 2

• Increasing degrees of freedom e.g.: lock wrist and elbow to find an acceptable movement solution, increasing axis increases the number of ways to gain the same outcome
• Kinematic movement variations
  ○ motor system noise - calcium binding, neuron pathway noise
  ○ planning errors /variability - 10x of the same thing, would you actually try to achieve it in the same way each time
  ○ feedback corrections - things that can be compensated
  ○ abundance/redundancy and covariation - interrelated, more DF than needed, can be made redundant if not needed.
  Covariation - things vary in a correlated way, relationship between 2 or more variables

Question 3

Describe the study of abundance, redundancy and covariation

Answer 3

e.g.: using 1 hand to press a button = needs to be 5 otherwise is wrong
If you use 2 hands there are different ways that 5 can be achieved (2+3, 4+1)
- But the second hand can be made redundant as it’s not really needed

Question 4

What are the 2 types of variability?

Answer 4

• outcome variability: variability in the result - result of human movement
• execution variability: kinematic variability - actual human movement

Question 5

What is the traditional approach to variability?

Answer 5

• we want outcome variability to be low
• As we learn we want to achieve a more consistent movement pattern → consistent outcome
• motor learning involves reduction of variability - best way to achieve the same outcome is to have the same execution
  
  • Baseball study (Fleisig et al., 2009)
  • 11 kinematic parameters (Fleisig et al., 2009)
    Quantified the (SD)variation in each of the 11 parameters - youth players had more variation than the pros

Question 6

Name the 2 sources of noise:

Answer 6

• motor commands (centrally) - motor commands, decision making
• sensorimotor systems (periphery) - muscle carrying out command
  As a skill is learnt there is an aim to reduce noise

Question 7

What was the aim of the Beers 2004 study?

How was it achieved?

Answer 7

to measure execution error

Had to touch a different target with their finger 30x, then randomised
To a different target(returning back to start each time)
- Tries to isolate execution error
- Small circles around each point shows execution variation as the same place isn’t touched each time
- 3 types of noise : signal-independent, signal-dependent, temporal

Question 8

Define:
- signal-independent
- signal-dependent
- temporal

Answer 8

• Signal-independent is constant noise from background activity of motoneurons
• Signal-dependent is the size of the noise, size of error was related to the noise and movement, in relation to firing of motor neurons and force production
• Temporal is timing variability, time of start to movement. Optimal level of temporal noise is almost identical to the coefficient of movement time variation shows that noise is moderately needed

Question 9

What is the dynamic approach to movement variability?

Answer 9

○ dynamical systems: variation has functional role ‘the bliss of motor abundance’ (Latash, 2012)
– adapt to external variables (solution space?)
– covariation
– feedback corrections
– reduce loading during repetitive activities - e.g.: variation of were the load is on a tissue during a marathon
‘the bliss of motor abundance’ (Latash, 2012

Question 10

Explain the solution space, Cohen 2008

Answer 10

Angle and speed of projectile can vary in the solution space
Different combinations of the 2 the success zone is the white zone
Trial 2 has a larger margin of error as there is a wider zone of success compared to trial 3
- Solution manifolds areas with greater sensitivity/tolerance to error are surrounded by larger areas in light grey shades
- aiming at more tolerant regions of the execution space reduces the effect of variability in execution on the result

Question 11

Name the 3 costs quantified by Muller 2003:

Answer 11

• tolerance cost: deviation from tolerant region
• noise cost: dispersion in execution variables
• covariation cost: not exploiting redundancy

Question 12

What is the:
- continuous relative phase
- state space

Answer 12

• Continuous relative phase - relative phase throughout the entire movement cycle is obtained, the difference between the phase angles of the two segments or joints
• State Space - made up from the relative system variables, and these are often times unknown, phase-plane in which the angular position is plotted against angular velocity

Question 13

Describe functional variability:

Answer 13

• variability can serve a functional purpose
• establish the effect on the task
• coaches should be aware of adjustments
• what perceptual information is used?
• provide specifying information in training