Evaluation of Muscle Synergy Flexibility Induced by a Muscle Nerve Block in Chronic Stroke Patients

Background: Drug treatments for gait disorders in post-stroke patients aim to reduce muscular hyperactivity. The analysis of muscle activity is essential to help clinicians understand these disorders. This study aimed to quantify changes in muscle synergies before (PRE) and after (POST) a rectus femoris nerve block. Methods: Gait analysis of 8 post-stroke patients before and immediately after nerve block. Muscle synergies were quantified from electromyographic signals. We have selected the account for variance, which indicates the effectiveness of the synergies, the recruitment selectivity index, which indicates the degree of multiplexing of the synergies, and the recruitment consistency index, which indicates the variability of the synergy activations across gait cycles. Results: A decrease in Variance Account For (VAF) is observed, showing a lack of robustness of the underlying muscle synergies between PRE and POST. We also note that spatial and temporal primitives result in different Index of Recruitment Selectivity (IRS) but similar Index of Recruitment Consistency (IRC) for PRE vs. POST. This shows that the synergies’ activations remain consistent across cycles but are more distributed in POST than in PRE. Conclusions: The motor nerve block has not created new muscle synergies of the paretic limb during gait but indicates that there is flexibility in motor organization. This method of quantification may enable clinicians to assess the motor adaptation potential of their post-stroke patients.