Functional Implications of Impaired Control of Submaximal Hip Flexion Following Stroke

Introduction: We quantified sub-maximal torque regulation during low to moderate intensity isometric hip flexion contractions in individuals with stroke and the associations with leg function. Methods: 10 participants with chronic stroke and 10 controls performed isometric hip flexion contractions at 5%, 10%, 15%, 20%, and 40% of maximal voluntary contraction (MVC) in paretic, non-paretic, and control legs. Results: Participants with stroke had larger torque fluctuations (coefficient of variation, CV), for both the paretic and non-paretic legs, than controls (Pr2 =0.45) and Berg Balance Score (r2=0.38). At 5% MVC, there were larger torque fluctuations in the contralateral leg during paretic contractions compared with the control leg. Conclusions: Impaired low-force regulation of paretic leg hip flexion can be functionally relevant and related to control versus strength deficits post stroke

The effects of notch filtering on electrically evoked myoelectric signals and associated motor unit index estimates

<p>Abstract</p> <p>Background</p> <p>Notch filtering is the most commonly used technique for suppression of power line and harmonic interference that often contaminate surface electromyogram (EMG) signals. Notch filters are routinely included in EMG recording instrumentation, and are used very often during clinical recording sessions. The objective of this study was to quantitatively assess the effects of notch filtering on electrically evoked myoelectric signals and on the related motor unit index measurements.</p> <p>Methods</p> <p>The study was primarily based on an experimental comparison of M wave recordings and index estimates of motor unit number and size, with the notch filter function of the EMG machine (Sierra Wave EMG system, Cadwell Lab Inc, Kennewick, WA, USA) turned on and off, respectively. The comparison was implemented in the first dorsal interosseous (FDI) muscle from the dominant hand of 15 neurologically intact subjects and bilaterally in 15 hemiparetic stroke subjects.</p> <p>Results</p> <p>On average, for intact subjects, the maximum M wave amplitude and the motor unit number index (MUNIX) estimate were reduced by approximately 22% and 18%, respectively, with application of the built-in notch filter function in the EMG machine. This trend held true when examining the paretic and contralateral muscles of the stroke subjects. With the notch filter on vs. off, across stroke subjects, we observed a significant decrease in both maximum M wave amplitude and MUNIX values in the paretic muscles, as compared with the contralateral muscles. However, similar reduction ratios were obtained for both maximum M wave amplitude and MUNIX estimate. Across muscles of both intact and stroke subjects, it was observed that notch filtering does not have significant effects on motor unit size index (MUSIX) estimate. No significant difference was found in MUSIX values between the paretic and contralateral muscles of the stroke subjects.</p> <p>Conclusions</p> <p>The notch filter function built in the EMG machine may significantly reduce the M wave amplitude and the MUNIX measurement. However, the notch filtering does not jeopardize the evaluation of the reduction ratio in maximum M wave amplitude and MUNIX estimate of the paretic muscles of stroke subjects when compared with the contralateral muscles.</p

Extracorporeal Shock Wave Stimulation as Alternative Treatment Modality for Wrist and Fingers Spasticity in Poststroke Patients: A Prospective, Open-Label, Preliminary Clinical Trial

Objective. To evaluate the effectiveness of radial shock waves (rESW) for wrist and fingers flexors spasticity in stroke patients. Methods. Twenty patients with upper limb muscle spasticity were enrolled in the study and treated with a single session of rESW. The spasticity level of the radio carpal (RC) and finger (FF) joints was assessed using Modified Ashworth Scale (MAS). The resting bioelectrical activity of the flexor carpi radialis (FCR) and flexor carpi ulnaris (FCU) was examined using surface electromyography (sEMG). Trophic conditions were measured using infrared thermal (IRT) imaging. All measurements were conducted at baseline (t0), immediately after rESW (t1), and 1 (t2) and 24 (t3) hours following rESW. Results. Significant reduction in MAS was observed for the RC joint in t1, as well as for the FF joints in t1, t2, and t3. A significant decrease in sEMG was shown for the FCR muscle in t1 and t2, as well as for the FCU muscle in t1 and t3. Also, a significant increase in IRT value was observed in t3 only. Conclusions. A single session of rESW could be an effective alternative treatment for reduction of limb spasticity and could lead to improvement of trophic conditions of the spastic muscles

Motor Unit Properties of the First Dorsal Interosseous in Chronic Stroke Subjects: Concentric Needle and Single Fiber EMG Analysis

The purpose of this study was to better understand changes in motor unit electrophysiological properties in people with chronic stroke based on concentric needle electromyography (EMG) and single fiber EMG recordings. The first dorsal interosseous (FDI) muscle was studied bilaterally in eleven hemiparetic stroke subjects. A significant increase in mean fiber density (FD) was found in the paretic muscle compared with the contralateral side based on single fiber EMG (1.6 ± 0.2 vs. 1.3 ± 0.1, respectively, P = 0.003). There was no statistically significant difference between the paretic and contralateral sides in most concentric needle motor unit action potential (MUAP) parameters, such as amplitude (768.7 ± 441.7 vs. 855.0 ± 289.9 μV), duration (8.9 ± 1.8 vs. 8.68 ± 0.9 ms) and size index (1.2 ± 0.5 vs. 1.1 ± 0.3) (P &gt; 0.18), nor was there a significant difference in single fiber EMG recorded jitter (37.0 ± 9.6 vs. 39.9 ± 10.6 μs, P = 0.45). The increase in FD suggests motor units of the paretic FDI have enlarged due to collateral reinnervation. However, sprouting might be insufficient to result in a statistically significant change in the concentric needle MUAP parameters. Single fiber EMG appears more sensitive than concentric needle EMG to reflect electrophysiological changes in motor units after stroke. Both single fiber and concentric needle EMG recordings may be necessary to better understand muscle changes after stroke, which is important for development of appropriate rehabilitation strategies. The results provide further evidence that motor units are remodeled after stroke, possibly in response to a loss of motoneurons

Assessing Side-Differences in the Organization of Biceps Brachii Motor Units in Healthy Subjects and Stroke Patients. An Evaluation from Surface EMG and Incremental Electrical Stimulation

Studies have suggested a degeneration of lower motoneurons in muscles affected after stroke, with a possible collateral reinnervation from the surviving motoneurons to the denervated muscle fibers. If this assumption holds, each surviving motoneuron would innervate a greater amount of muscle fibers following stroke, i.e., motor units’ size would increase in muscles affected after stroke. By combining neuromuscular electrical stimulation with surface electromyography, the present PhD thesis aimed at investigating whether muscle reinnervation following stroke leads to greater variations in the amplitude of M waves elicited in muscles of the affected side of stroke patients, with respect to the contralateral, unaffected side. This issue was verified by applying current pulses at progressively greater intensities in the motoneurons that supply the biceps brachii muscle. Then, the size of increases in the amplitude of M waves elicited consecutively, hereafter defined as increments, was considered to evaluate structural adaptations in biceps brachii motor units following stroke. Changes in the amplitude of M waves evoked in a muscle is usually assumed to reflect changes in the number of motoneurons and, consequently, of muscle fibers activated. Hence, we hypothesized that for similar, relative increases in current intensity, greater increments in the M-waves amplitude would be observed in muscles of the affected than unaffected side of stroke patients. Before verifying this hypothesis, however, we investigated whether the size of increments in biceps brachii M waves differ between arms of healthy subjects. This question was motivated by the fact that, usually, humans tend to control more finely the muscle force production in dominant than non-dominant upper limbs. Once it is well established the recruitment of motor units is a key mechanism for which muscle force is controlled, we hypothesized that a relatively smaller number of motor units maybe recruited in muscles of dominant than nondominant limbs, for any given increase in synaptic input. Hence, we expected to observe smaller increments in the amplitude of M waves evoked in biceps brachii of dominant than non-dominant arms. This PhD thesis was, therefore, based on two main researches, entitled: (1) “Does the biceps brachii muscle respond similarly in both limbs during staircase, electrically elicited contractions?” and (2) “Assessing structural adaptation of biceps brachii motor units after stroke”. Both studies were investigated with the same methodological approach mentioned above. Our main findings showed that: (1) increments were significantly smaller in biceps brachii of dominant than non-dominant arms. These results suggest there was a more gradual motor units’ recruitment and, therefore, a broader spectrum of motor units’ recruitment thresholds in muscles of dominant than non-dominant arms, which may contribute for a finer regulation of force production; (2) there was a clear trend towards greater increments in the amplitude of M waves elicited in biceps brachii of the affected than unaffected arms of most of the stroke patients evaluated. Although for few of these patients it was not clear whether side-differences in the increments magnitude were an outcome of dominance or stroke, the results found corroborate with the notion that collateral reinnervation takes place after stroke, increasing the number of muscle fibers per unit and, therefore, the magnitude of the muscle responses. Overall, the findings of this PhD thesis strengthen the idea that the organization of the neuromuscular system may contribute to accounting for upper limb dominance and that stroke may lead to structural adaptations in motor units of affected muscles

Flexor Dysfunction Following Unilateral Transient Ischemic Brain Injury Is Associated with Impaired Locomotor Rhythmicity

Functional motor deficits in hemiplegia after stroke are predominately associated with flexor muscle impairments in animal models of ischemic brain injury, as well as in clinical findings. Rehabilitative interventions often employ various means of retraining a maladapted central pattern generator for locomotion. Yet, holistic modeling of the central pattern generator, as well as applications of such studies, are currently scarce. Most modeling studies rely on cellular neural models of the intrinsic spinal connectivity governing ipsilateral flexor-extensor, as well as contralateral coupling inherent in the spinal cord. Models that attempt to capture the general behavior of motor neuronal populations, as well as the different modes of driving their oscillatory function in vivo is lacking in contemporary literature. This study aims at generating a holistic model of flexor and extensor function as a whole, and seeks to evaluate the parametric coupling of ipsilateral and contralateral half-center coupling through the means of generating an ordinary differential equation representative of asymmetric central pattern generator models of varying coupling architectures. The results of this study suggest that the mathematical predictions of the locomotor centers which drive the dorsiflexion phase of locomotion are correlated with the denervation-type atrophy response of hemiparetic dorsiflexor muscles, as well as their spatiotemporal activity dysfunction during in vivo locomotion on a novel precise foot placement task. Moreover, the hemiplegic solutions were found to lie in proximity to an alternative task-space solution, by which a hemiplegic strategy could be readapted in order to produce healthy output. The results revealed that there are multiple strategies of retraining hemiplegic solutions of the CPG. This solution may modify the hemiparetic locomotor pattern into a healthy output by manipulating inter-integrator couplings which are not damaged by damage to the descending drives. Ultimately, some modeling experiments will demonstrate that the increased reliance on intrinsic connectivity increases the stability of the output, rendering it resistant to perturbations originating from extrinsic inputs to the pattern generating center

Muscle Coordination Contributes to Function after Stroke; Proprioception Contributes to Control of Posture, Movement

More than half of stroke survivors experience persistent upper extremity motor impairments that can negatively impact quality of life and independence. Effective use of the upper extremity requires coordination of agonist/antagonist muscle pairs, as well as coordination of multiple control actions for stabilizing and moving the arm. In this dissertation, I present three studies in which I recorded isometric torque production, single joint movement and stabilization, and clinical measures of function and impairments after stroke to evaluate the extent to which changes in coordination of agonist/antagonist muscles and of sequential control actions contribute to deficits after stroke. In Aim 1, I quantified the extent to which stroke-related deficits in the coordination of agonist/antagonist muscle pairs degraded the ability to generate, maintain, and relax cued torques about the elbow. Participants who survived stroke (SP) and neurologically intact participants (NI) performed pursuit tracking of step-changes in isomeric torque targets to investigate coordination of activation magnitude in elbow agonist/antagonist muscle pairs. SP had marked hypertonia of the primary flexor muscles, which led to increased compensatory activity in the primary extensor muscles. These stroke-related deficits of muscle coordination degraded ability to generate, maintain, and relax cued torque production. In Aim 2, SP and NI performed sequential combinations of elbow stabilization and movements to investigate impairments in execution and coordination of these fundamental control actions. Impaired proprioception in SP was associated with increased impairments in stabilizing the arm against a perturbation compared with SP with intact proprioception. Surprisingly, SP with intact proprioception had greater impairments when moving than did SP with impaired proprioception. These results support the supposition that deficits of somatosensation can differentially impact neural control of limb stabilization and movement. Aim 3 used correlation and forward regression to compare deficits of muscle coordination (Aim 1) and control (Aim 2) to one another in order to quantify the extent to which each could explain deficits of motor function after stroke. Taken together, the three studies revealed that stroke-related deficits in coordination timing and magnitude of muscle activation impact clinically-measured function, and that somatosensory deficits can differentially impair neuromotor stabilization and movement control

Motor Compensation During Lower Limb Pedaling After Stroke

Long-term motor dysfunction in the lower limb is common after stroke. One potential contributor is motor compensation, a behavior in which functions originally performed by the paretic limb are performed by the non-paretic limb. Compensation in chronic stroke may contribute to long-term motor dysfunction by limiting functional ability, impairing future recovery, and eliciting maladaptive neuroplasticity. The purpose of this dissertation was to describe the impact of compensation on motor function and brain activation during lower limb pedaling and identify elements that produce this behavior. To achieve this purpose, we evaluated muscle activation and motor performance when compensation was prevented. During unilateral pedaling, paretic muscle activation increased but motor performance deteriorated. During bilateral uncoupled pedaling, paretic muscle activation further increased. However, subjects were unable to coordinate movements of the legs, and motor performance further deteriorated. These results suggest that compensation improves motor performance but limits paretic motor output. Because motor performance was worse during bilateral uncoupled than unilateral pedaling, impaired interlimb coordination may be a primary factor leading to compensation. As a follow-up, we determined whether altered interlimb spinal reflex pathways contribute to impaired interlimb coordination after stroke. Interlimb cutaneous reflexes were elicited during pedaling, and we assessed whether the amplitude was altered. Interlimb reflex was altered, particularly in bifunctional muscles and at pedaling transitions. Reflex alterations were correlated with impairments in interlimb coordination and compensation. These data suggest that stroke-related changes in interlimb reflex pathways undermine interlimb coordination. Finally, we assessed whether altered motor commands and performance, such as seen with compensation, are related to decreased pedaling-related brain activation after stroke. Brain activation was measured during volitional pedaling and during passive pedaling, when between-group differences were minimized. Between-group differences in brain activation persisted during passive pedaling, suggesting that altered motor commands and pedaling performance do not account for reduced brain activation after stroke. Overall, these studies provide insight into rehabilitative interventions that may decrease long-term motor dysfunction in the lower limb after stroke. One potential strategy is to enhance paretic muscle activity by preventing compensation while simultaneously employing efforts to improve interlimb coordination, possibly by manipulating interlimb reflex pathways