Muscle Control Analysis of Human Walking and Cycling in Speed and Load Variations With Time-Varying Synergy

Walking and cycling are vital motor activities in rehabilitation and athletic training. Its in-depth movement analysis is essential in understanding muscle control because it provides insight into how muscles are coordinated during daily activities. Electromyography (EMG) offers measures regarding multiple muscles’ spatiotemporal activity patterns. However, it is a challenging task to capture small changes in muscle coordination that may occur, especially when the same motion task is given with different mechanical conditions since the overall muscle usage is similar but with minor modulations. The muscle synergy hypothesis, prominent within this domain, proposes that our central nervous system simplifies motor controls by coordinating sets of muscles as cohesive units, addressing the complexity of human movement. While earlier studies illuminated the spatial coordination aspects via spatial synergy, they often overlooked the common temporal dynamics over repeated trials. In our research, we employed time-varying synergy to elucidate distinct spatiotemporal muscle modulations in walking and cycling across a range of speeds and loads. Specifically, we identified two muscle synergy patterns in walking and cycling, each with unique characteristics. Importantly, these muscle synergies exhibited adaptive properties, fine-tuning both the amplitude and temporal onset of synergy activation for speed variation conditions, but not for load conditions. In the case of cycling, the synergy during the extension demonstrated a more important role than the flexion. In addition, there was a striking correlation between synergy attributes and pedaling roughness. The results indicate that pedaling is more efficient for those who can maintain constant timing of synergy application.