Identifying representative synergy matrices for describing muscular activation patterns during multidirectional...

Area of Science:

• Neuroscience
• Biomechanics
• Motor Control

Background:

• Muscle synergies simplify movement generation by the central nervous system (CNS).
• Understanding these synergies is crucial for movement restoration technologies like functional electrical stimulation (FES).

Purpose of the Study:

• To investigate if a limited set of muscle synergies can describe multijoint upper limb reaching tasks across various directions.
• To determine if these synergies are common across multiple movement directions.

Main Methods:

• Recorded surface electromyographic (EMG) signals from 12 upper limb muscles in healthy men.
• Used nonnegative matrix factorization to extract muscle synergies from EMG envelopes during single-joint and multijoint reaching tasks.
• Analyzed movement kinematics using a motion analysis system.

Main Results:

• A multijoint reaching task in 12 directions was accurately described (R² > 0.85) by a linear combination of synergies.
• Four synergies from individual joint movements or three synergies from multijoint movements could capture task variations.
• Synergies extracted from multiple directions were common and reduced dimensionality.

Conclusions:

• A limited set of muscle synergies can generate diverse multijoint upper limb movements.
• These findings support the use of muscle synergy principles for developing effective FES-based movement restoration strategies.