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.
"The decreased amplitude reflected the decrease in force production capacity of the upper extremity muscles normally observed after stroke
. Stroke-induced damages in the corticospinal system
 and muscle atrophy caused by long-term disuse
 may account for the reduced amplitude of force production and the decreased accuracy displayed by the subjects after stroke. Previous study reported that subjects after stroke and healthy participants performed tasks at 10%, 20%, and 30% of maximal voluntary contraction
[Show abstract][Hide abstract] ABSTRACT: Background
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.
A customized dynamometer with force sensors was used to measure grip force and calculate rotation torque during the sub-maximal grip control tasks. The paretic and nonpartic sides of eleven subjects after stroke and the dominant sides of ten healthy persons were tested. Their maximal voluntary grip force was measured and used to set sub-maximal grip control tasks at three different target force levels. Force control ability was characterized by the maximal grip force, mean force percentage, coefficient of variation (CV), target deviation ratio (TDR), and rotation torque ratio (RTR). The motor impairments of subjects after stroke were also evaluated using the Fugl-Meyer assessment for upper extremity (FMA-UE) and Wolf Motor Function Test (WMFT).
Maximal grip force of the paretic side was significantly reduced as compared to the nonparetic side and the healthy group, while the difference of maximal grip force between the nonparetic side and the healthy group was not significant. TDR and RTR increased for all three groups with increasing target force level. There were significant differences of CV, TDR and RTR between the paretic side and the healthy group at all the force levels. CV, TDR and RTR showed significant negative correlations with FMA-UE and WMFT at 50% of maximum grip force.
This study designed a customized dynamometer together with an innovative measurement, RTR, to investigate the hand motor performance of subjects after mild to moderate stroke during force control tasks. And stroke-induced abnormal flexion synergy of wrist and finger muscles could be characterized by RTR. This study also identified a set of kinetic parameters which can be applied to quantitatively assess the hand motor function of subjects after mild to moderate stroke.
Journal of NeuroEngineering and Rehabilitation 05/2014; 11(1):84. DOI:10.1186/1743-0003-11-84 · 2.74 Impact Factor
"As widely described in literature, a cerebrovascular accident affects the ability of patients to effectively control their arms during complex motor tasks. Specifically, subjects who experienced a stroke usually show weakness and slowness while moving their arm, difficulty while generating and sustaining force, and delayed muscle contraction [1-3]. Moreover, a cerebrovascular accident alters the ability to selectively recruit muscle groups during upper limb related motor tasks [4-7], and involves strong torque coupling among muscles crossing elbow and shoulder joints [8-10]. "
[Show abstract][Hide abstract] 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. DOI:10.1186/1743-0003-10-103 · 2.74 Impact Factor
"Hemiparesis is a common motor impairment in individuals who sustained a cerebrovascular accident (CVA) (National Stroke Association , 2006), and is characterized by changes on motor control including muscle weakness and tonus alterations (Colebatch et al., 1986; Bourbonnais and Vanden-Noven, 1989; National Stroke Association, 2006; Lindquist et al., 2007). Upper limb impairments in the paretic and in the non-paretic sides lead to voluntary reaching deficits and hence to restrictions on the ability to perform activities of daily living which directly affects the autonomy of these individuals (Zackowski et al., 2004; Schaefer et al., 2007; Smania et al., 2009). "
[Show abstract][Hide abstract] ABSTRACT: OBJECTIVE: To analyze electromyographic (EMG) patterns and isokinetic muscle performance of shoulder abduction movement in individuals who sustained a cerebrovascular accident (CVA). DESIGN: Twenty-two individuals who sustained a CVA and 22 healthy subjects volunteered for EMG activity and isokinetic shoulder abduction assessments. EMG onset time, root mean square (RMS) for upper trapezius and deltoid muscles, as well as the isokinetic variables of peak torque, total work, average power and acceleration time were compared between limbs and groups. RESULTS: The paretic side showed a different onset activation pattern in shoulder abduction, along with a lower RMS for both muscles (21.8±13.4% of the maximal voluntary isometric contraction (MVIC) for the deltoid and 25.9±15.3% MVIC for the upper trapezius, about 50% lower than the control group). The non-paretic side showed a delay in both muscles activation and a lower RMS for the deltoid (32.2±13.7% MVIC, about 25% lower than the control group). Both sides of the group of individuals who sustained a CVA presented a significantly lower isokinetic performance compared to the control group (paretic side ∼60% lower; non-paretic side ∼35% lower). CONCLUSIONS: Shoulder abduction muscle performance is impaired in both paretic and non-paretic limbs of individuals who sustained a CVA.
Journal of electromyography and kinesiology: official journal of the International Society of Electrophysiological Kinesiology 01/2013; 23(3). DOI:10.1016/j.jelekin.2012.12.001 · 1.65 Impact Factor
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