Stability of reaching during standing in stroke

Area of Science:

• Neuroscience
• Biomechanics
• Motor Control

Background:

• Reaching from a standing position requires complex coordination of focal (arm movement) and postural (body stability) systems.
• Individuals with stroke often exhibit deficits in motor control, affecting their ability to perform multi-joint movements like reaching.

Purpose of the Study:

• To investigate the ability of individuals with stroke to stabilize both the endpoint trajectory and the center-of-mass (COM) during standing reaches.
• To analyze how kinematic redundancy is utilized to manage multiple task goals in stroke survivors during reaching.

Main Methods:

• Utilized the uncontrolled manifold (UCM) approach to analyze endpoint and COM trajectories during voluntary reaches in 19 stroke survivors and 11 healthy controls.
• Segment angles were used as elemental variables, and a synergy index (SI) quantified the stability of endpoint and COM trajectories (SI_END and SI_COM).

Main Results:

• Both groups maintained a stable COM synergy index (SI_COM) throughout the reaching movement.
• Stroke survivors demonstrated significantly greater variability in endpoint trajectory stabilization (lower SI_END) compared to healthy individuals, particularly at peak movement velocity.
• Despite reduced endpoint stability, stroke survivors effectively utilized kinematic redundancy to maintain COM stability.

Conclusions:

• Individuals with stroke prioritize COM stability over endpoint trajectory control during reaching from standing.
• The findings highlight that motor deficits after stroke involve difficulties in coordinating focal and postural adjustments.
• Therapeutic strategies for stroke recovery should address the simultaneous stabilization of both endpoint and postural elements to improve reaching performance.