L16 synergy

Synergy in Kinesiology

• Definition of Synergy
  • Originates from Greek, meaning "work together", implying coordinated effort.
  • In kinesiology, refers to the highly coordinated and often subconscious actions of multiple limbs, joints, and muscles working synchronously to produce efficient and stable movement.
  • Terminology is often inconsistent across different fields and researchers, leading to multiple interpretations and ongoing scientific debate about its precise meaning and measurement.

Historical Context

• Early conceptions linked synergy with movement disorders, notably observed by neurologists like Hughlings Jackson, Babinski, and physiotherapists like Bobath.
  • Hughlings Jackson's work described how neurological lesions could lead to "release phenomena" where the nervous system defaulted to fixed, inflexible patterns of movement.
  • Babinski identified involuntary associated movements, or synergistic reactions, in patients with neurological damage.
  • Bobath developed rehabilitation techniques based on inhibiting abnormal reflex activity and breaking up stereotypical synergistic patterns often seen post-stroke.
• These patterns of muscle activation observed post-stroke or other neurological conditions are often obligatory, fixed, and can significantly interfere with normal, voluntary, and fractionated movement.

Terminology

• "Synergy" has diverse meanings depending on the context and theoretical framework:
  • Synergy-A:
  • Refers to stereotypical muscle activation patterns that are often pathological and related to neurological disorders (e.g., flexion or extension synergies in stroke patients).
  • Characterized by limited modulation: the activation is non-task-specific, meaning the same pattern is elicited regardless of the specific demands of the movement, impeding fine motor control.
  • Synergy-B:
  • Describes groups of variables (e.g., muscle modes, joint angles) that tend to scale together in a coordinated fashion during movement.
  • These are non-obligatory and allow for task-dependent adjustments, providing a flexible framework for motor control where elements are functionally linked but not rigidly fixed.
  • Synergy-C:
  • Denotes task-specific stability patterns, typically identified through the analytical framework of the Uncontrolled Manifold (UCM) concept.
  • These synergies represent the nervous system's ability to exploit motor redundancy by organizing joint and muscle variability to stabilize a critical performance variable, ensuring consistent task outcomes even with internal noise.

Uncontrolled Manifold (UCM) Concept

• A key principle of UCM is that variance within the UCM (variability that does not affect task performance, $V ext{<em>}{UCM}$) must significantly exceed variance orthogonal to the UCM (variability that negatively impacts task performance, $V ext{</em>}{Orth}$) for synergy to be established ($V ext{<em>}{UCM} > V ext{</em>}{Orth}$).
• V ext{_}{UCM} represents inter-trial variance and flexibility that is