Motor Modules are Impacted by the Number of Reaching Directions Included in the Analysis.

Area of Science:

• Biomechanics
• Neuroscience
• Motor Control

Background:

• Muscle synergy analysis is a key method for understanding neural control of human movement.
• This analysis relies on dimensionality reduction techniques to extract muscle synergies from activation data.
• Current methods often assume a limited set of movements adequately represents all possible movements.

Purpose of the Study:

• To investigate the impact of the number and selection of reaching directions on the validity of extracted muscle synergies.
• To determine the minimum number of reaching directions required for reliable muscle synergy analysis.

Main Methods:

• A musculoskeletal model was used to simulate muscle activations for 36 planar reaches.
• Nonnegative matrix factorization (NMF) and principal component analysis (PCA) were applied to extract muscle synergies.
• Subsets of reaches were analyzed to assess the representativeness of extracted synergies.

Main Results:

• A minimum of 6 reaching directions were found to be necessary for extracting valid muscle synergies.
• Reducing the number of reaches below 6 altered the composition of the extracted synergies.
• The specific choice of reaching directions, even with sufficient numbers, influenced synergy validity.

Conclusions:

• Both the quantity and selection of reaching directions are critical factors in muscle synergy analysis.
• The findings highlight the importance of carefully choosing movement data for accurate neural coordination studies.
• This research provides crucial insights for optimizing experimental design in motor control research.