Synergies Flashcards
What is a motor synergy?
- More precise definition for human movement will include:
- More than one part of neuromusculoskeletal system is involved(more than 1 segment/ muscle)
- Is controlled by CNS (not passive) and has intention (not inherent) - CNS intends to do
- Work together towards a common goal
What are the 3 views of a motor synergy?
- Anatomical synergists or agonists
- move joint in same direction e.g.: biceps and triceps working antagonistically
- Joint moment synergists
- generate moment in same direction e.g.: bicep brachaii and brachialis
- Task synergist / antagonists
- action assists or resists task performance e.g.: other muscles coming in to stop unwanted movement
What does a synergy do?
- Reduces dimensionality - making a common pathway to control the movement, reduces the number of systems from the brain = less controls
- Less controls needed for many degrees of freedom
- Potentially reduces demands on CNS
- Potentially reduces errors in performance, less inputs can lead to less errors in outputs
- Links to Uncontrolled Manifold Hypothesis
Describe the UCM hypothesis:
- Relates to task-specific stability in a redundant system (Schöner, 1995)
- System acts in multidimensional space of elemental variables (degrees of freedom = axis)
- Organises a sub-space (UCM) related to a desired performance of task-specific variable - if this requires 1 element, it creates a 1D space, 2 elements = 2D space etc
- Covariance of elemental variables to keep variance in UCM and reduced variance in task, elements work together to reduce variability
ORTH axis represents variation in our task performance
Only care about variance on ORTH line as it creates variance in our performance
What are kinematic synergies?
- Kinematic variables (i.e., joint angles) viewed as the elemental variables:
- Scholz and Schöner (1999) – sit to stand, small variance in outcome, which is tiny compared to variability in how they stand
- Scholz et al. (2000) – pistol shooting, reduced variability in shot outcome
- Both confirm multi-joint synergies (VUCM > VORT) that stabilises performance
What are kinetic variables?
- Kinetic variables (i.e., force/moment) viewed as the elemental variables - forces producing the kinematic synergies
- Latash et al. (2001) – finger forces
- Shim et al. (2005) – gripping (prehension)
- Confirm central strategies of solving tasks with common control (again VUCM > VORT) - indicates a synergy exists, all elements working together
- space has no effect on the task-specific performance variable.
Describe muscle synergies:
- Muscle activations (EMG) viewed as the elemental variables, different axis that are variable
- Difficult to create link between activations on mechanics as in previous
- Examine covariation within activations(EMG signals themselves) - if they move together, indicates central control
- Computer simulation studies
- Movement that has fewer synergies, reproduce suboptimal movement, more synergies increases skill of movement.
What is the role of the weight of a pattern?
How does changing the weight alter the movement?
Fundamental signals are the same for every muscle, they just have different weights to differentiate them
- By changing the weight of the pattern, we can create a new movement(discrete values for different controls)
- Changing the patterns without changing the weight will change the pattern of movement in each individual muscle
How do synergies change with practice?
- Adjustments to mode/muscle weights
- Adjustments to mode time series
- Reductions in variation of task performance
- Reduction then increase in variation of non-task performance (UCM)
What is the effect of
- UCM
- ORTH
variation?
Variation along the UCM = good variation
Variation along ORTH = bad variation(in task performance - can be reduced with practise(line gets thinner on a graph)
