Merging and Fractionation of Muscle Synergy Indicate the Recovery Process in Patients with Hemiplegia: The First Study of Patients after Subacute Stroke

Abstract

Loss of motor coordination is one of the main problems for patients after stroke. Muscle synergy is widely accepted as an indicator of motor coordination. Recently, the characteristics of muscle synergy were quantitatively evaluated using nonnegative matrix factorization (NNMF) with surface electromyography. Previous studies have identified that the number and structure of synergies were associated with motor function in patients after stroke. However, most of these studies had a cross-sectional design, and the changes in muscle synergy during recovery process are not clear. In present study, two consecutive measurements were conducted for subacute patients after stroke and the change of number and structure of muscle synergies during gait were determined using NNMF. Results showed that functional change did not rely on number of synergies in patients after subacute stroke. However, the extent of merging of the synergies was negatively associated with an increase in muscle strength and the range of angle at ankle joint. Our results suggest that the neural changes represented by NNMF were related to the longitudinal change of function and gait pattern and that the merging of synergy is an important marker in patients after subacute stroke.

Changes in leg cycling muscle synergies after training augmented by functional electrical stimulation in subacute stroke survivors: a pilot study

“…However, these changes were not reflected in an increase of synergy complexity, neither in terms of number of synergies extracted nor in terms of VAF 1 . These results confirmed that synergy complexity during cycling did not consistently change with the recovery of function soon after stroke as already observed by Hashigushi et al when analyzing muscle synergies during walking [24]. Possible explanations could be that in our sample, a number of synergies comparable with that of healthy subjects was obtained by all subjects at baseline, differently from [11], or the limited duration of the training, lasting only 3 weeks.…”

“…Indeed, a better timing of the ankle plantar flexor module and an increased number of modules were found which overall improved the walking performance of chronic stroke patients. Conversely, in another study evaluating longitudinal changes in modular motor coordination during locomotion in subacute stroke survivors, no substantial changes in the number of motor synergies were found after 1 month of conventional therapy [24]. Finally, in the most recent study on subacute stroke survivors an increased lateral symmetry in muscle synergies while walking, associated with improvements in gait kinematics measurements, was found after 3 weeks of walking training supported by a lower limb exoskeleton [25].…”

“…Few studies explored the changes of muscle synergies after a rehabilitative intervention [20][21][22][23][24][25]. Two of them were focused on upper limb motor recovery in chronic stroke patients [20,21].…”

“…One study investigated muscle synergies changes during walking in children with Cerebral Palsy [22]. The remaining three studies observed longitudinal changes in stroke survivors during locomotion [23][24][25]. Routson and colleagues [23] observed that 12 weeks of treadmill training with body weight support were able to influence module composition and timing.…”

Peer Review #2 of "Not all brawn, but some brain. Strength gains after training alters kinematic motor abundance in hopping (v0.2)"

“…In contrast, prospective resistance training studies of the upper limb demonstrated that greater wrist and finger strength was associated with greater abundance in finger force coordination tasks (Olafsdottir et al 2008;Park et al 2015;Shim et al 2008). Resistance training may augment motor abundance via several mechanisms: (1) by increasing reciprocal inhibition of covarying muscle groups via heteronomous spinal pathways (Geertsen et al 2008), (2) increasing the role of bi-articular muscles in inter-segmental kinematic co-variation (Cleather et al 2015), and (3) increasing the number of muscle modes available for co-variation (Hashiguchi et al 2016).…”