Effects of early and intensive neuro-rehabilitative treatment on muscle synergies in acute post-stroke patients: a pilot study

Abstract

BackgroundAfter a stroke, patients show significant modifications of neural control of movement, such as abnormal muscle co-activation, and reduced selectivity and modulation of muscle activity. Nonetheless, results reported in literature do not allow to unequivocally explain whether and, in case, how a cerebrovascular accident affects muscle synergies underlying the control of the upper limb. These discrepancies suggest that a complete understanding of the modular re-organization of muscle activity due to a stroke is still lacking. This pilot study aimed at investigating the effects of the conjunction between the natural ongoing of the pathology and the intense robot-mediated treatment on muscle synergies of the paretic upper limb of subacute post-stroke patients.MethodsSix subacute patients, homogenous with respect to the age and the time elapsed from the trauma, and ten healthy age-matched subjects were enrolled. The protocol consisted in achieving planar movement of the upper limb while handling the end-effector of a robotic platform. Patients underwent 6 weeks long treatment while clinical scores, kinematics of the end-effector and muscle activity were recorded. Then we verified whether muscle coordination underlying the motor task was significantly affected by the cerebrovascular accident and how muscle synergies were modified along the treatment.ResultsResults show that although muscle synergies in subacute stroke patients were qualitatively comparable to those of healthy subjects, those underlying the movement of the shoulder can reflect the functional deficit induced by the pathology. Moreover, the improvement of motor performance due to the treatment was achieved in conjunction with slight modifications of muscle synergies. In this regard, modifications of muscle synergies appeared to be influenced by the different recovering mechanisms across patients presumably due to the heterogeneity of lesions, sides and location of the accident.ConclusionsThe results support the hypothesis that muscle synergies reflect the injury of the cerebrovascular accident and could document the effects of the functional recovery due to a suitable and customized treatment. Therefore, they open up new possibilities for the development of more effective neuro-rehabilitation protocols.

Synergy analysis as a tool to design and assess an effective stroke rehabilitation

“…It is remarkable that the number of synergies extracted is low compared to other studies carried out in the upper limb [7,9,10]. We speculate this may be due to the relative simplicity of the tested movements (involving 1 -2 DOFs) and the selected VAF threshold.…”

“…Thus, VAF could constitute a simple neuromuscular measure of movement control accuracy. It has to be noted that in this study, all subjects were right handed to ensure a homogeneous population similar to most stroke patients studied in literature [10]. However, results are discussed in terms of dominant and nondominant limbs, thus it is logical that the same apply to left-handed subjects but in the opposite arm.…”

“…However, little is known about how rehabilitation impacts SA. Results suggest that rehabilitation-guided motor improvement is accompanied by slight changes in synergy structure [10]. Similarly, authors described a synergy-based impairment index that got closer to healthy values after training [11].…”

“…In contrast, withinsubject interlimb SA remains considerably conserved showing important structural similarities. In [7,8,10], authors compare stroke and healthy populations and report that the greatest SA alteration corresponds to synergy activation. Here, we show that interlimb activation patterns in healthy subjects are very similar (~80%).…”

“…However, it is sill to be proven that SA similarity between the affected and unaffected limbs indicates physiological recovery. In fact a pilot study in acute patients reports that similarity of muscle synergies between healthy and stroke patients did not increase after recovery [10], although interlimb comparisons were not considered.…”