Investigation of Power Specific Motor Primitives in an Upper Limb Rotational Motion

Area of Science:

• Biomechanics
• Motor Control
• Neuroscience

Background:

• Muscle synergies (MS) are fundamental to understanding how the nervous system controls complex human movements.
• Investigating MS during cyclical tasks like cycling provides insights into motor planning and execution.

Purpose of the Study:

• To examine muscle synergies (MS) in the upper limb during hand-cycling across a range of power outputs (20-120 watts).
• To determine if the number and structure of muscle synergies change with varying cycling intensities.

Main Methods:

• Electromyographic (EMG) signals from 7 upper limb muscles were recorded during hand-cycling.
• Non-Negative Matrix Factorization (NNMF) was employed to extract muscle synergies.
• Cosine similarity and cross-correlation analyzed synergy structure and activation patterns.

Main Results:

• A consistent set of three muscle synergies explained over 95% of the variance across all tested power levels.
• The fundamental structure of these synergies, representing push and pull mechanisms, remained stable.
• Modulation was observed in the activation coefficients of these synergies, indicating adaptability.

Conclusions:

• Upper limb cycling relies on a stable set of muscle synergies regardless of power output.
• Motor adaptation to different cycling intensities is achieved through adjustments in synergy activation, not by altering synergy composition.