stretch reflexes
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2021 ◽  
Author(s):  
Zoe Villamar ◽  
Daniel Ludvig ◽  
Eric J Perreault

AbstractThe spinal stretch reflex is a fundamental building block of motor function, modulating sensitivity across tasks to augment volitional control. Stretch reflex sensitivity can vary continuously during movement and changes between movement and posture. While there have been many demonstrations of reflex modulation and investigations into the underlying mechanisms, there have been few attempts to provide simple, quantitative descriptions of the relationship between the volitional control and stretch reflex sensitivity throughout tasks that require the coordinated activity of several muscles. Here we develop such a description and use it to test the hypothesis that the modulation of stretch reflex sensitivity during movement can be explained by the balance of activity within the relevant agonist and antagonist muscles better than by the activity only in the muscle homonymous with the elicited reflex. We applied continuous pseudo-random perturbations of elbow angle as subjects completed approximately 500 movements in elbow flexion and extension. Measurements were averaged across the repeated movements to obtain continuous estimates of stretch reflex amplitude and background muscle activity. We also ran a control experiment on a subset of subjects performing postural tasks at muscle activity levels matched to those measured in the movement task. For both experiments, we assessed the relationship between background activity in the agonist and antagonist muscles controlling elbow movement and the stretch reflexes elicited in them. We found that modulation in the stretch reflexes during movement can be described by modulation of the background activity in the agonist and antagonist muscles, and that models incorporating agonists and antagonists are significantly better than those considering only the homonymous muscle. Increases in agonist muscle activity enhanced stretch reflex sensitivity whereas increases in antagonist activity suppressed reflex activity. Surprisingly, the magnitude of these effects was similar, suggesting a balance of control between agonists and antagonist that is very different than the dominance of sensitivity to agonist activity during postural tasks. This greater relative sensitivity to antagonist background activity during movement is due to a large decrease in sensitivity to homonymous muscle activity during movement rather than substantial changes in the influence of antagonist muscle activity.


Author(s):  
Eline Flux ◽  
Marjolein M. van der Krogt ◽  
Jaap Harlaar ◽  
Annemieke I. Buizer ◽  
Lizeth H. Sloot

Abstract Background As hyperactive muscle stretch reflexes hinder movement in patients with central nervous system disorders, they are a common target of treatment. To improve treatment evaluation, hyperactive reflexes should be assessed during activities as walking rather than passively. This study systematically explores the feasibility, reliability and validity of sudden treadmill perturbations to evoke and quantify calf muscle stretch reflexes during walking in children with neurological disorders. Methods We performed an observational cross-sectional study including 24 children with cerebral palsy (CP; 6–16 years) and 14 typically developing children (TD; 6–15 years). Short belt accelerations were applied at three different intensities while children walked at comfortable speed. Lower leg kinematics, musculo-tendon lengthening and velocity, muscle activity and spatiotemporal parameters were measured to analyze perturbation responses. Results We first demonstrated protocol feasibility: the protocol was completed by all but three children who ceased participation due to fatigue. All remaining children were able to maintain their gait pattern during perturbation trials without anticipatory adaptations in ankle kinematics, spatiotemporal parameters and muscle activity. Second, we showed the protocol’s reliability: there was no systematic change in muscle response over time (P = 0.21–0.54) and a bootstrapping procedure indicated sufficient number of perturbations, as the last perturbation repetition only reduced variability by ~ 2%. Third, we evaluated construct validity by showing that responses comply with neurophysiological criteria for stretch reflexes: perturbations superimposed calf muscle lengthening (P < 0.001 for both CP and TD) in all but one participant. This elicited increased calf muscle activity (359 ± 190% for CP and 231 ± 68% for TD, both P < 0.001) in the gastrocnemius medialis muscle, which increased with perturbation intensity (P < 0.001), according to the velocity-dependent nature of stretch reflexes. Finally, construct validity was shown from a clinical perspective: stretch reflexes were 1.7 times higher for CP than TD for the gastrocnemius medialis muscle (P = 0.017). Conclusions The feasibility and reliability of the protocol, as well as the construct validity—shown by the exaggerated velocity-dependent nature of the measured responses—strongly support the use of treadmill perturbations to quantify stretch hyperreflexia during gait. We therefore provided a framework which can be used to inform clinical decision making and treatment evaluation.


2021 ◽  
Vol 126 (4) ◽  
pp. 1015-1029
Author(s):  
Ronald C. van ’t Veld ◽  
Edwin H. F. van Asseldonk ◽  
Herman van der Kooij ◽  
Alfred C. Schouten

Previous research and definitions of the stretch reflex and spasticity have focused on velocity dependence. We showed that perturbation acceleration, velocity, and duration all shape the M1 and M2 response, often via nonlinear or interacting dependencies. Consequently, systematic execution and reporting of stretch reflex and spasticity studies, avoiding uncontrolled parameter interdependence, is essential for proper understanding of the reflex neurophysiology.


Author(s):  
Philipp Maurus ◽  
Isaac L. Kurtzer ◽  
Ryan Antonawich ◽  
Tyler Cluff

Limb dominance is evident in many daily activities leading to the prominent idea that each hemisphere of the brain specializes in controlling different aspects of movement. Past studies suggest the dominant arm is primarily controlled via an internal model of limb dynamics that enables the nervous system to produce efficient movements. In contrast, the non-dominant arm may be primarily controlled via impedance mechanisms that rely on the strong modulation of sensory feedback from individual joints to control limb posture. We tested whether such differences are evident in behavioral responses and stretch reflexes following sudden displacement of the arm during posture control. Experiment 1 applied specific combinations of elbow-shoulder torque perturbations (the same for all participants). Peak joint displacements, return times, endpoint accuracy, and the directional tuning and amplitude of stretch reflexes in nearly all muscles were not statistically different between the two arms. Experiment 2 induced specific combinations of joint motion (the same for all participants). Again, peak joint displacements, return times, endpoint accuracy, and the directional tuning and amplitude of stretch reflexes in nearly all muscles did not differ statistically when countering the imposed loads with each arm. Moderate to strong correlations were found between stretch reflexes and behavioral responses to the perturbations with the two arms across both experiments. Collectively, the results do not support the idea that the dominant arm specializes in exploiting internal models and the non-dominant arm in impedance control by increasing reflex gains to counter sudden loads imposed on the arms during posture control.


2021 ◽  
Vol 125 (4) ◽  
pp. 1339-1347
Author(s):  
Jeffrey Weiler ◽  
Paul L. Gribble ◽  
J. Andrew Pruszynski

We have previously shown that spinal circuits can rapidly generate reflex responses that efficiently engage multiple joints to support postural hand control of the upper limb. Here, we show that spinal circuits can also rapidly generate such efficient responses during reaching actions.


2021 ◽  
Vol Publish Ahead of Print ◽  
Author(s):  
Luisa Marilena Schäck ◽  
Thomas Schöttker-Königer ◽  
Christian Sturm ◽  
Christoph Gutenbrunner ◽  
Alexander Ranker

2020 ◽  
Vol 124 (3) ◽  
pp. 985-993
Author(s):  
Litsa Nikitidou Ledri ◽  
Jessica Pingel ◽  
Hans Hultborn ◽  
Eva Rudjord Therkildsen ◽  
Jacob Wienecke ◽  
...  

Immobilization leads to multiple simultaneous adaptive changes in muscle, connective tissue, and central nervous system.


2020 ◽  
Vol 30 (18) ◽  
pp. R1025-R1030 ◽  
Author(s):  
Sasha Reschechtko ◽  
J. Andrew Pruszynski
Keyword(s):  

2020 ◽  
Vol 81 ◽  
pp. 99-100
Author(s):  
E. Flux ◽  
R.C. van ’t Veld ◽  
M.M. van der Krogt ◽  
E.H.F. van Asseldonk

2020 ◽  
Vol 238 (7-8) ◽  
pp. 1627-1636
Author(s):  
Jens Bo Nielsen ◽  
Mark Schram Christensen ◽  
Simon Francis Farmer ◽  
Jakob Lorentzen

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