Myoelectric interface training enables targeted reduction in abnormal muscle co-activation

Abstract

Background Abnormal patterns of muscle co-activation contribute to impaired movement after stroke. Previously, we developed a myoelectric computer interface (MyoCI) training paradigm to improve stroke-induced arm motor impairment by reducing the abnormal co-activation of arm muscle pairs. However, it is unclear to what extent the paradigm induced changes in the overall intermuscular coordination in the arm, as opposed to changing just the muscles trained with the MyoCI. This study examined the intermuscular coordination patterns of thirty-two stroke survivors who participated in 6 weeks of MyoCI training. Methods We used non-negative matrix factorization to identify the arm muscle synergies (coordinated patterns of muscle activity) during a reaching task before and after the training. We examined the extent to which synergies changed as the training reduced motor impairment. In addition, we introduced a new synergy analysis metric, disparity index (DI), to capture the changes in the individual muscle weights within a synergy. Results There was no consistent pattern of change in the number of synergies across the subjects after the training. The composition of muscle synergies, calculated using a traditional synergy similarity metric, also did not change after the training. However, the disparity of muscle weights within synergies increased after the training in the participants who responded to MyoCI training—that is, the specific muscles that the MyoCI was targeting became less correlated within a synergy. This trend was not observed in participants who did not respond to the training. Conclusions These findings suggest that MyoCI training reduced arm impairment by decoupling only the muscles trained while leaving other muscles relatively unaffected. This suggests that, even after injury, the nervous system is capable of motor learning on a highly fractionated level. It also suggests that MyoCI training can do what it was designed to do—enable stroke survivors to reduce abnormal co-activation in targeted muscles. Trial registration This study was registered at ClinicalTrials.gov (NCT03579992, Registered 09 July 2018—Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT03579992?term=NCT03579992&draw=2&rank=1)

Muscle synergies for evaluating upper limb in clinical applications: A systematic review

“…Stroke-related studies had the largest number of participants, including in total of 850 individuals, and 609 of them were patients. Seven studies recruited over 30 patients [ 43 , [86] , [87] , [88] , [89] , [90] , [91] ]. The number of patients and healthy subjects in each study is shown in Fig.…”

“…However, considering the limitation of practical applications, especially for patients, MVC is often difficult to measure. In this review, twenty-one studies reported the employment of alternative normalization methods, which were classified into five types: MVC (9.52%, percentage of the studies) [ 99 , 102 ], maximum value (MAX, 38.1%) [ 60 , 89 , 90 , 92 , 93 , 98 , 119 , 131 ], average value (AVE, 9.52%) [ 101 , 127 ], or median value (MED, 14.29%) [ 104 , 110 , 115 ] of the amplitude of the recorded EMG signals, and unit variance (UVA, 28.57%) [ 75 , 91 , 95 , 108 , 124 , 125 ].…”

Developing new intermuscular coordination patterns through an electromyographic signal-guided training in the upper extremity

“…The signi cance of the similarity score of the muscle synergies in comparison was tested by computing the similarity score of all possible pairs of a random synergy set, 1000 synergies randomly selected from the entire synergy sets identi ed in this study. The 95th percentile level of the similarity scores computed from the random synergy sets was used as a similarity threshold (Th sim = 0.78) [30,36,50,52] to determine the signi cance of a similarity score of muscle synergies.…”

Muscle Synergies In Joystick Manipulate Task : Evaluation Of Inter-Group Variability

“…This suggests that muscle synergies may be formed by adaptive processes in relationship to the experiences of each individual. Long-term training can target abnormal coactivation, particularly of the most abnormally co-activating muscle pair 42 . Consequently, the relatively concentrated similarity of muscle synergies observed between the group A (Fig 8)…”