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- Modulation of ankle antagonist co-activation during the transition from upright standing to gait and to sit in post-stroke subjectsPublication . Ribeiro, Edgar; Silva, Augusta; Pinho, Liliana; Santos, Rubim; Pinho, Francisco; Pinheiro De Sousa, Andreia SofiaAntagonist co-activation represents a neuronal command for the modulation of muscle synergies with postural control purposes, probably assuming a key role in the characterisation of tonus dysfunction in post-stroke subjects. This study aims to evaluate the ankle antagonist co-activation during different functional tasks in post-stroke subjects. The CONTRA limb presented decreased values in TA/SOL pair during upright standing and increased values in both muscle pairs during gait initiation compared to the IPSI limb (Table 1). No significant differences were found between tasks (Table 1). he IPSI and CONTRA limbs presented increased antagonist co-activation when an adequate antigravity function and the coordination of the tibia forward rotation are required, respectively. The comparison of these values with that obtained by healthy subjects seems to point to a bilateral postural control dysfunction in post-stroke subjects related to tonus modulation deficits that should be addressed in neurorehabilitation. Future studies with a higher sample are required to extend the results.
- Intrinsic and functional stiffness vs. antagonist co-activation: a correlational analysis in stroke patientsPublication . Ribeiro, Edgar; Silva, Augusta; Pinho, Liliana; Rubim, Santos; Pinho, Francisco; Pinheiro De Sousa, Andreia SofiaTonus has been considered the basis of central nervous system (CNS) functional adaptation to fulfill the dual purpose of movement and postural control [1]. Among the multiple pathologies of CNS, stroke has been the most investigated in the context of tonus dysfunction, typically through measures involving the evaluation of muscle resistance against stretching at rest [2]. However, the recent evidence demonstrating that the increased muscle resistance obtained under these conditions is more related to intrinsic compo- nents, being not associated to movement dysfunction [3], turn relevant the assessment of biomechanical variables that could reflect tonus dysfunction in a highly demanding postural control functional context, like upright standing [4] and postural phases of gait initiation and stand-to-sit [5, 6]. By representing muscle synergies organization within postural tone to increase joint stiffness and postural stability, antagonist co- activation at the ankle level would reflect tonus dysfunction in poststroke subjects [7]. Furthermore, the evaluation of ankle stiffness through the analysis of stabilometric data obtained by a force platform during a functional task such as upright standing [8], here called functional stiffness, may also be used as a func- tional alternative to intrinsic stiffness assessment. Based on the previously exposed, it can be hypothe- sized that functional stiffness, rather than intrinsic stiffness, would best reflect the muscle synergies in- volved in the maintenance of postural stability during functional tasks. The main aim of the present study was to evaluate the level of correlation between intrinsic stiffness at rest, functional stiffness in upright standing and antagonist co-activation in upright standing and postural phases of gait initiation and stand-to-sit, at the ankle joint of post-stroke subjects.
- Correlation between ankle stiffness and antagonist co-activation in post-stroke subjectsPublication . Ribeiro, Edgar; Silva, Augusta; Pinho, Liliana; Santos, Rubim; Pinho, Francisco; Sousa, Andreia S. P.Tonus dysfunction has been broadly investigated in post-stroke subjects through the evaluation of muscle resistance against stretching, however, its characterisation in functional context is challenging. This study aims to analyse the correlation between intrinsic stiffness, functional stiffness and antagonist co-activation at the ankle joint of post-stroke subjects. Both lower limbs of eight post-stroke participants were evaluated. Intrinsic stiffness was assessed during passive dorsiflexion by an isokinetic dynamometer, functional stiffness during upright standing on a force platform and antagonist co-activation was obtained in upright standing and postural phases of gait initiation and stand-to-sit through the electromyographic signal of ankle muscles.