NEURO-MECHANICS OF RECUMBENT LEG CYCLING IN POST-ACUTE STROKE PATIENTS

Introduction: Cycling training is widely used in post-stroke rehabilitation to improve motor function and aerobic capacity. However, the specific alterations in the modular control of cycling soon after a stroke have not been fully analyzed. This study aims to explore these alterations by examining electromyography (EMG) signals from nine leg muscles and pedal forces during recumbent pedaling in post-acute stroke patients. The findings could provide valuable insights into the potential use of cycling as both a rehabilitation method and an assessment tool for post-stroke patients.

Key Findings: The study involved 16 post-acute stroke patients and 12 age-matched healthy controls. EMG signals and pedal forces were measured bilaterally during recumbent pedaling. Patients also walked over a GaitRite mat to compute standard gait parameters. Four muscle synergies were extracted through nonnegative matrix factorization (NNMF) from healthy subjects and the unaffected legs of patients. In the affected sides of patients, two to four synergies were identified, with the number of synergies significantly correlating with the Motricity Index (Spearman’s coefficient = 0.521). The reduction in coordination complexity resulted in reduced biomechanical performance, particularly in patients with only two muscle synergies, who exhibited the lowest work production and mechanical effectiveness in the affected leg. These patients also showed locomotor impairments, such as reduced gait speed, asymmetrical stance time, and prolonged double support time. Significant correlations were found between cycling-based metrics and gait parameters, suggesting that neuro-mechanical quantities of pedaling can inform walking dysfunctions. These findings support the use of pedaling in stroke rehabilitation, especially in the early phase when patients may be unable to perform safe and active gait training.

Muscle Synergies and EMG Analysis: The study used surface EMG signals recorded bilaterally from nine leg muscles during recumbent pedaling. These signals were analyzed to extract muscle synergies, which are patterns of muscle co-activation. Four muscle synergies were consistently identified in healthy subjects and the unaffected legs of patients. However, in the affected sides of patients, the number of synergies varied from two to four, with fewer synergies correlating with higher motor impairment. This reduction in synergies indicates a loss of complexity in muscle coordination, which impacts biomechanical performance. Patients with fewer synergies showed significantly lower work production and mechanical effectiveness in the affected leg, emphasizing the importance of coordination complexity for motor function.

Biomechanical Performance and Gait Parameters: The study also examined the biomechanical performance of patients during pedaling and their gait parameters during walking. Patients with fewer muscle synergies in the affected leg exhibited lower work production and mechanical effectiveness during pedaling. These patients also demonstrated significant locomotor impairments, including reduced gait speed, asymmetrical stance time, and prolonged double support time. The correlation between cycling-based metrics and gait parameters suggests that the neuro-mechanical aspects of pedaling can provide valuable insights into walking dysfunctions. This finding underscores the potential of using cycling not only as a rehabilitation method but also as an assessment tool to evaluate motor impairment and recovery in post-stroke patients.

Cycling-Based Metrics: Several cycling-based metrics were extracted from the pedal force profiles and reconstructed synergy activation coefficients. These metrics included work production, index of effectiveness, area symmetry index, and shape symmetry index. The work produced by the affected leg increased with the number of muscle synergies but remained lower than that of the unaffected leg and healthy subjects. The index of effectiveness showed significant unbalance between the two sides for all subjects, with the lowest effectiveness observed in the two-module sub-group of patients. The area symmetry index and shape symmetry index revealed that patients with fewer synergies had less superposition and similarity in force profiles and synergy activation patterns compared to healthy subjects. These metrics provide a quantitative analysis of lower limb motor impairment and can be used to monitor recovery and guide rehabilitation strategies.

Conclusion: This study provides a detailed analysis of the modular control of cycling in post-acute stroke patients, revealing a reduction in muscle coordination complexity in the affected leg. The findings support the use of cycling as a rehabilitation method and an assessment tool for post-stroke patients, particularly in the early phase of recovery. By examining muscle synergies and biomechanical performance, clinicians can gain valuable insights into motor impairment and develop targeted interventions to enhance motor function and recovery. The proposed cycling-based metrics offer a comprehensive and quantitative approach to evaluating lower limb motor impairment and guiding rehabilitation efforts for stroke patients.

Join the Discussion: We invite you to share your thoughts on the implications of these findings for stroke rehabilitation. Do you think cycling-based assessments could revolutionize the way we approach post-stroke recovery? How do you see the integration of muscle synergy analysis in clinical practice? Join the conversation in the comments below and share your insights on how these discoveries could shape future rehabilitation strategies.

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Original Research: The original research, "Neuro-Mechanics of Recumbent Leg Cycling in Post-Acute Stroke Patients," can be found on PubMed here.