Two-muscle coordination versus natural treadmill locomotion.

Area of Science:

• Neuroscience
• Motor Control
• Human Locomotion

Background:

• Previous research demonstrated single-muscle learned behaviors acted as independent units during treadmill locomotion.
• Learned behaviors can influence existing motor patterns, prompting investigation into how muscle ensembles coordinate.
• Understanding muscle synergy is crucial for deciphering complex human movement patterns.

Purpose of the Study:

• To investigate if a learned double-muscle behavior harmoniously integrates with or competes against natural human treadmill locomotion.
• To explore the neural mechanisms underlying the coordination of learned and natural motor patterns.
• To assess the capacity of operant conditioning in shaping complex, multi-muscle motor ensembles.

Main Methods:

• Developed a novel double-muscle learned behavior requiring in-phase bilateral rectus femoris (RF) activity.
• Utilized computer-assisted operant conditioning, triggered by a visual cue post-left heel strike, to train the new motor pattern.
• Assessed the integration of the learned behavior with natural treadmill locomotion in four adult participants.

Main Results:

• The double-muscle learned behavior was acquired rapidly (1-6 days) by all participants.
• Participants largely maintained harmonious stepping with minimal changes in step cycle timing.
• Significant modifications in leg positioning were observed, indicating complex neural adaptations.
• The learned behavior integrated effectively with natural locomotion, rather than competing with it.

Conclusions:

• Operant conditioning is a powerful tool for constructing complex, fine-grained motor behaviors.
• Learned multi-muscle ensembles can integrate harmoniously with natural human locomotion.
• Complex neural mechanisms govern the coordination of learned and innate motor patterns, influencing interlimb coordination.