Modular control of muscle coordination patterns during various stride time and stride length combinations

Area of Science:

• Biomechanics
• Motor Control
• Neuroscience

Background:

• Muscular control is typically organized into synergistic muscle groups hierarchically.
• Conflicting views exist on whether this modular organization is consistent across different walking speeds.
• Variations in stride time and stride length may explain these discrepancies.

Purpose of the Study:

• To investigate if the regulation of modular muscle organization during walking depends on stride time and stride length combinations.
• To explore the adaptability of muscle synergies across different gait parameters.

Main Methods:

• Ten healthy men walked at a moderate speed (0.4 nondimensional speed) employing five distinct stride time-length combinations.
• Surface electromyograms (EMG) were recorded from 16 trunk and lower limb muscles.
• Muscle synergies were extracted using a decomposition technique, and the number and duration of synergy activations were analyzed.

Main Results:

• The number of muscle synergies was consistent for preferred and quasi-preferred walking conditions (median: 4.5-5 synergies).
• Synergy numbers varied significantly at extreme stride conditions (very short: 4, very long: 6 synergies).
• Gait parameters differed significantly between preferred and quasi-preferred conditions (p < 0.03).

Conclusions:

• Modular control during walking exhibits flexibility, with synergy activations fine-tuned even at a single walking speed.
• Consistent muscle synergies can produce a variety of walking patterns, except for extreme gait variations.
• This suggests that the central nervous system can adapt muscle activation patterns to achieve different gait parameters.