Altered multijoint reflex coordination is indicative of motor impairment level following stroke

Abstract

Following stroke, individuals often are unable to activate their elbow and shoulder muscles independently. There is growing evidence that altered reflex pathways may contribute to these abnormal patterns of activation or muscle synergies. Most studies investigating reflex function following stroke have examined only individual joints at rest. Thus, the purpose of this study was to quantify multijoint reflex contributions to the stereotyped muscle synergies commonly observed following stroke. We hypothesized that the patterns of reflex coordination mirror the abnormal muscle coactivity patterns previously reported for voluntary activation. 10 chronic stroke and 8 agematched control subjects participated. Reflexes were elicited by perturbing the arm with a 3 degree of freedom robot while subjects exerted voluntary forces at the elbow and shoulder. The force conditions tested were selected to assess the influence of gravity and the influence of joint torque generation without gravity on reflex coordination. Reflex magnitude was quantified by the average rectified electromyogram, recorded from 8 muscles that span the elbow and shoulder. Patterns of reflex coordination were quantified using independent components analysis. Results show significant reflex coupling between elbow flexor and shoulder abductor-extensor muscles in stroke patients during isolated elbow and shoulder torque generation and during active arm support against gravity. Identified patterns of stretch reflex coordination were consistent with the stereotyped voluntary flexion synergy, suggesting reflex pathways contribute to abnormal muscle coordination following stroke.

The ACT-4D: A novel rehabilitation robot for the quantification of upper limb motor impairments following brain injury

“…In most, subjects where asked to maintain a constant amount of biceps activation [10], [19]- [24] with 1-DOF devices. In [25], investigators used a 3-DOF robot to quantify multi-joint reflex contributions to abnormal muscle synergies. However, none of the devices used have the degrees of freedom and performance characteristics necessary to investigated the influence of the volitional drive, high movement speeds and high amounts of shoulder loading on the flexion synergy and stretch reflexes.…”

Potential of robots as next-generation technology for clinical assessment of neurological disorders and upper-limb therapy

“…The capability of robots to apply discrete perturbations make them ideal for quantifying reflexive behavior and, notably, exploring more complex long-latency responses that cannot be elicited with a hammer tap [55]. For example, a recent study using robots to apply multijoint perturbations of the arm highlighted how patterns of muscle activity tend to generate multijoint flexor synergies in subjects with stroke [56].…”

Towards evidence-based classification for paralympic running and throwing events

“…Hypertonia results in: the inability to isolate movement; perform movements consistently; an increase in the presence of involuntary contractions (spasm); and an impaired ability to sequence muscle activity to avoid undesirable muscle synergies (Sanger et al 2003, Trumbower et al 2008.…”

“…Evidence suggests that during reaching tasks, people presented with significant reflex coupling of the elbow flexor and shoulder abductor-extensor muscles when attempting to produce isolated elbow and shoulder activities (Trumbower et al 2008). This suggests that hypertonia contributes to abnormal muscle coordination in functional reaching tasks (Trumbower et al 2008). In sport, the ability to isolate joints or produce a sequential movement is important for throwing.…”