Background
Muscle
synergies analysis can provide a deep understanding of motor impairment
after stroke and of changes after rehabilitation. In this study, the
neuro-mechanical analysis of leg cycling was used to longitudinally
investigate the motor recovery process coupled with cycling training
augmented by Functional Electrical Stimulation (FES) in subacute stroke
survivors.
Methods
Subjects
with ischemic subacute stroke participated in a 3-week training of
FES-cycling with visual biofeedback plus usual care. Participants were
evaluated before and after the intervention through clinical scales,
gait spatio-temporal parameters derived from an instrumented mat, and a
voluntary pedaling test. Biomechanical metrics (work produced by the two
legs, mechanical effectiveness and symmetry indexes) and bilateral
electromyography from 9 leg muscles were acquired during the voluntary
pedaling test. To extract muscles synergies, the Weighted Nonnegative
Matrix Factorization algorithm was applied to the normalized EMG
envelopes. Synergy complexity was measured by the number of synergies
required to explain more than 90% of the total variance of the
normalized EMG envelopes and variance accounted for by one synergy.
Regardless the inter-subject differences in the number of extracted
synergies, 4 synergies were extracted from each patient and the
cosine-similarity between patients and healthy weight vectors was
computed.
Results
Nine
patients (median age of 75 years and median time post-stroke of
2 weeks) were recruited. Significant improvements in terms of clinical
scales, gait parameters and work produced by the affected leg were
obtained after training. Synergy complexity well correlated to the level
of motor impairment at baseline, but it did not change after training.
We found a significant improvement in the similarity of the synergy
responsible of the knee flexion during the pulling phase of the pedaling
cycle, which was the mostly compromised at baseline. This improvement
may indicate the re-learning of a more physiological motor strategy.
Conclusions
Our
findings support the use of the neuromechanical analysis of cycling as
a method to assess motor recovery after stroke, mainly in an early
phase, when gait evaluation is not yet possible. The improvement in the
modular coordination of pedaling correlated with the improvement in
motor functions and walking ability achieved at the end of the
intervention support the role of FES cycling in enhancing motor
re-learning after stroke but
need to be confirmed in a controlled study
with a larger sample size.
Trial registration
ClinicalTrial.gov,
NCT02439515. Registered on May 8, 2015, .
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