Weakness in patients with hemiparesis.
ABSTRACT Clinical and experimental results are reviewed concerning muscle weakness in patients with hemiparesis after a stroke. The discussion includes the important role that alterations in the physiology of motor units, notably changes in firing rates and muscle fiber atrophy, play in the manifestation of muscle weakness. This role is compared with the lesser role that spasticity (defined as hyperactive stretch reflexes) of the antagonist muscle group appears to play in determining the weakness of agonist muscles. The contribution of other factors that result in mechanical restraint of the agonist by the antagonist (e.g., passive mechanical properties and inappropriate cocontraction) is discussed relative to muscle weakness in patients with hemiparesis.
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ABSTRACT: After 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. Six 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. Results 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. The 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.Journal of NeuroEngineering and Rehabilitation 10/2013; 10(1):103. · 2.57 Impact Factor
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ABSTRACT: The purpose of this study was to analyze the change in antagonist co-activation ratio of upper-limb muscle pairs, during the reaching movement, of both ipsilesional and contralesional limbs of post-stroke subjects, comparing, respectively, to dominant and non-dominant limbs of healthy subjects. Nine healthy and nine post-stroke subjects were instructed to reach and grasp a target, placed in the sagittal and scapular planes of movement. Surface EMG was recorded from postural control and movement related muscles: latissimus dorsi (LD), sternal head of pectoralis major (PM), anterior (AD) and posterior (PD) segments of deltoid, biceps brachii (BB), brachioradialis (BR), and triceps lateral (TRIlat). Reaching movement was divided in two sub-phases, according to proximal postural control versus movement control demands, during which antagonist co-activation ratios were calculated for the muscle pairs LD/PM, PD/AD, TRIlat/BB and TRIlat/BR. Post-stroke’s ipsilesional limb presented lower co-activation in muscles with an important role in postural control (LD/PM), comparing to the dominant limb of healthy subjects during the first sub-phase, when the movement was performed in the sagittal plane (p<0.05). Conversely, the post-stroke’s contralesional limb showed in general an increased co-activation ratio in muscles related to movement control, comparing to the non-dominant limb of healthy subjects. Statistical differences were found for the muscle pair TRllat/BB during the first sub-phase of the reaching movement, when the movement was performed in the sagittal plane (p<0.05), and during the second sub-phase, for the muscle pairs LD/PM (p<0.05, in the sagittal plane of movement, and PD/AD, in both sagittal (p<0.05) and scapular (p<0.05) planes of movement. Our findings demonstrate that, in post-stroke subjects, the reaching movement performed with the ipsilesional upper limb seems to show co-activation impairments in muscle pairs associated to postural control, whereas the contralesional upper limb seems to have signs of impairment of muscle pairs related to movement.Journal of Electromyography and Kinesiology. 01/2014;
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ABSTRACT: The aim of this study is to investigate quantitative outcome measurements of hand motor performance for subjects after mild to moderate stroke using grip control tasks and characterize abnormal flexion synergy of upper extremities after stroke.Journal of NeuroEngineering and Rehabilitation 05/2014; 11(1):84. · 2.57 Impact Factor