Relationship between stretch reflex thresholds and voluntary arm muscle activation in patients with spasticity

Abstract

Previous studies have shown that deficits in agonist-antagonist muscle activation in the single-joint elbow system in patients with spastic hemiparesis are directly related to limitations in the range of regulation of the thresholds of muscle activation. We extended these findings to the double-joint, shoulder-elbow system in these patients. Ten non-disabled individuals and 11 stroke survivors with spasticity in upper limb muscles participated. Stroke survivors had sustained a single unilateral stroke 6-36 months previously, had full pain-free passive range of motion of the affected shoulder and elbow and had some voluntary control of the arm. EMG activity from four elbow and two shoulder muscles was recorded during quasi-static (<5 degrees /s) stretching of elbow flexors/extensors and during slow voluntary elbow flexion/extension movement through full range. Stretches and active movements were initiated from full elbow flexion or extension with the shoulder in three different initial positions (60 degrees , 90 degrees , 145 degrees horizontal abduction). SRTs were defined as the elbow angle at which EMG signals began to exceed 2SD of background noise. SRT angles obtained by passive muscle stretch were compared with the angles at which the respective muscles became activated during voluntary elbow movements. SRTs in elbow flexors were correlated with clinical spasticity scores. SRTs of elbow flexors and extensors were within the biomechanical range of the joint and varied with changes in the shoulder angle in all subjects with hemiparesis but could not be reached in this range in all healthy subjects when muscles were initially relaxed. In patients, limitations in the regulation of SRTs resulted in a subdivision of all-possible shoulder-elbow arm configurations into two areas, one in which spasticity was present ("spatial spasticity zone") and another in which it was absent. Spatial spasticity zones were different for different muscles in different patients but, taken together, for all elbow muscles, the zones occupied a large part of elbow-shoulder joint space in each patient. The shape of the boundary between the spasticity and no-spasticity zones depended on the state of reflex inter-joint interaction. SRTs in single- and double-joint flexor muscles correlated with the positions at which muscles were activated during voluntary movements, for all shoulder angles, and this effect was greater in elbow flexor muscles (brachioradialis, biceps brachii). Flexor SRTs correlated with clinical spasticity in elbow flexors only when elbow muscles were at mid-length (90 degrees ). These findings support the notion that motor impairments after CNS damage are related to deficits in the specification and regulation of SRTs, resulting in the occurrence of spasticity zones in the space of elbow-shoulder configurations. It is suggested that the presence of spatial spasticity zones might be a major cause of motor impairments in general and deficits in inter-joint coordination in particular in patients with spasticity.

Diagnostic accuracy of common clinical tests for assessing abdominal muscle function after motor-complete spinal cord injury above T6

“…14,15 For both EMG and ultrasound data, if the average root mean square amplitude or muscle thickness of the two contraction trials for a given muscle and task exceeded 2 s. d. above the mean resting value (calculated from all trials), the value was defined as 'present' for the given technique and was included in the frequency analysis. [18][19][20] For each task, only the appropriate muscles were included to determine presence of response (flexion: bilateral RA; rotation: ipsilateral TrA/OI and contralateral OE; lateral bending: ipsilateral OE; hollowing: bilateral TrA/OI and Valsalva: all muscles).…”

Effects of Integrated Volitional Control Electrical Stimulation (IVES) on Upper Extremity Function in Chronic Stroke

“…The root mean square (RMS) of the EMG signal was calculated over the entire duration of the signal (duration of contraction and voltage time wave of the EMG signal) from the onset to the termination. As a measure of hypertonicity, the coactivation ratio, defined as the ratio of the RMS of the antagonist muscles to that of the antagonist plus agonist muscles, 14 was calculated by measuring the RMS from 10 EMG recordings during active palmar or dorsal flexion movements.…”

Avaliação eletromiográfica dos músculos do membro superior de indivíduos hemiparéticos com uso da Terapia do Espelho.

“…Musampa et al 18 demonstraram, em um estudo com 10 indivíduos saudáveis e 11 indivíduos pós-AVE, através da EMG de superfície, alteração na regulação do reflexo de estiramento entre agonistas/antagonistas dos grupos musculares flexores e extensores do cotovelo, devido à hipertonia dos flexores dos pacientes com espasticidade e, visto que a regulação do reflexo de estiramento tem sido descrita como mecanismo principal de controle da postura e do movimento em indivíduos saudáveis, sugeriram a avaliação de ambos os membros superiores de indivíduos pós-AVE, e não somente no hemicorpo acometido pela hemiparesia. Os resultados encontrados em nosso estudo corroboram os achados de Musampa et al 18 e de Gerachshenko et al 19 , nos quais constatou-se atividade muscular antagonista (extensora) durante o repouso no membro superior de indivíduos hemiparéticos.…”