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

Sex comparisons of agonist and antagonist muscle electromyographic parameters during two different submaximal isometric fatiguing tasks

© 2019 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society. To examine the task failure time of the force- and position-based submaximal elbow flexion fatiguing tasks for both sexes, twelve men and eight women visited the laboratory for two separate experimental occasions. During the experiment, they pulled against a rigid restraint for the force task and maintained a constant elbow joint angle to support an equivalent inertial load for the position task. For both fatiguing tasks (50% of the isometric strength at the elbow joint angle of 135 degree), the task failure time, along with the surface electromyographic (EMG) amplitude and mean frequency (MNF) were measured. The average failure time was longer for the force task than that for the position task (sexes combined: 39.6 ± 16.6 sec vs. 33.9 ± 14.9 sec, P = 0.033). In addition, men were overall less fatigable than women (tasks combined: 42.0 ± 14.7 sec vs. 28.7 ± 10.3 sec, P = 0.020). The multiple regression analyses showed that the task failure time in women was solely predicted by the rate of change of the triceps EMG MNF. Thus, more fatigability of women in this study was likely due to the quicker fatiguing rate of the antagonist triceps brachii muscle. Different from most previous studies that have used 90-degree elbow joint angle, the current 135-degree joint angle setup might have created a situation where greater muscle activity from the related muscles (e.g., the antagonist) were required for women than for men to stabilize the joint, thereby resulting in a shorter task failure time

Examining error detection capabilities in a novel force production task as a function of athletic experience.

The purpose of this experiment is to determine whether having previous athletic experience in a routine sport (ie. Cheerleading) will affect the participant’s ability to self-report superior error-detection, motor performance, time on target, confidence, and agonist and antagonist co-activation patterns while learning a novel skill compared to non-routine athletes. Participants were required to perform proportions of their maximal isometric elbow flexion (46%) and extension (38%) forces for 5 seconds over 30 acquisition trials on an elbow flexion and extension device. Following each trial, participants will be required to estimate how much force they think they exerted on that trial as well as their confidence on that trial. A feedback screen was provided regarding what their task goal was, their actual performance, and their estimated performance. A no-KR (Knowledge of Results) retention and transfer test was conducted approximately 48-hours after the acquisition period. Meanwhile, we examined the co-activation patterns in the EMG (electromyography) of their biceps and triceps as they performed their isometric contractions. During the acquisition, retention, and transfer periods there were no between group differences for error detection, motor performance, time on target, confidence, nor for muscle co-activation. The present study found that skill level of the participant does not affect error-detection accuracy and decreases muscle co-activation when learning a novel skill

Effect of Age, Elbow Muscle Co-Contraction Level, and Elbow Moment Loading Charachteristics on Elbow Angle Positional Variability in Postural Tasks.

Hand positional variability during a task confounds many activities of daily living, such as inserting a key into a lock, pouring hot water into a cup, and eating with a spoon. Current dogma suggests that older adults use increased co-contraction to attenuate hand positional variability; however, this has not been proven. This thesis proposes that elbow muscle co-contraction significantly affects elbow angle positional variability (PV), which affects hand positional variability, and that older adults can reduce their PV by decreasing their co-contraction level. Variable muscle stiffness was incorporated into the Signal Dependent Noise Theory to model the effect of elbow muscle co-contraction on predicted PV during a quasistatic elbow flexion task. The results demonstrated an optimal level of co-contraction that minimized the positional variability for both variable and constant loading paradigms. The first experiment tested the effect of greater than natural elbow muscle co-contraction levels on PV. Fourteen younger and 14 older healthy adults resisted both constant and variable external elbow extension moments while co-contracting at different levels. Increasing co-contraction was found to increase positional variability for both younger and older adults (p < 0.005). Older adults naturally co-contracted at higher levels and had lower positional variability than younger adults (p < 0.005). The second experiment tested the effect of below-natural elbow muscle co-contraction levels on PV in 14 younger and 14 older healthy adults. The effect of age was not significant in predicting positional variability at the lowered co-contraction level. In the third experiment, 12 younger and 14 older healthy adults poured water through different sized container openings. Older subjects co-contracted at higher levels and had lower PV than younger adults. While co-contraction increased with decreasing target size, increased co-contraction within a pouring target size increased PV (p < 0.05) and decreased pouring accuracy (p < 0.001). We conclude that increasing elbow muscle co-contraction increases PV and hinders the performance of tasks, such as pouring, that require low positional variability. This counters the current belief that high co-contraction levels are beneficial for task performance, and suggests that people who struggle with these tasks may benefit from reduced co-contraction.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91474/1/mtgordon_1.pd

Neuromechanical Tuning for Arm Motor Control

Movement is a fundamental behavior that allows us to interact with the external world. Its importance to human health is most evident when it becomes impaired due to disease or injury. Physical and occupational rehabilitation remains the most common treatment for these types of disorders. Although therapeutic interventions may improve motor function, residual deficits are common for many pathologies, such as stroke. The development of novel therapeutics is dependent upon a better understanding of the underlying mechanisms that govern movement. Movement of the human body adheres to the principles of classic Newtonian mechanics. However, due to the inherent complexity of the body and the highly variable repertoire of environmental contexts in which it operates, the musculoskeletal system presents a challenging control problem and the onus is on the central nervous system to reliably solve this problem. The neural motor system is comprised of numerous efferent and afferent pathways with a hierarchical organization which create a complex arrangement of feedforward and feedback circuits. However, the strategy that the neural motor system employs to reliably control these complex mechanics is still unknown. This dissertation will investigate the neural control of mechanics employing a “bottom-up” approach. It is organized into three research chapters with an additional introductory chapter and a chapter addressing final conclusions. Chapter 1 provides a brief description of the anatomical and physiological principles of the human motor system and the challenges and strategies that may be employed to control it. Chapter 2 describes a computational study where we developed a musculoskeletal model of the upper limb to investigate the complex mechanical interactions due to muscle geometry. Muscle lengths and moment arms contribute to force and torque generation, but the inherent redundancy of these actuators create a high-dimensional control problem. By characterizing these relationships, we found mechanical coupling of muscle lengths which the nervous system could exploit. Chapter 3 describes a study of muscle spindle contribution to muscle coactivation using a computational model of primary afferent activity. We investigated whether these afferents could contribute to motoneuron recruitment during voluntary reaching tasks in humans and found that afferent activity was orthogonal to that of muscle activity. Chapter 4 describes a study of the role of the descending corticospinal tract in the compensation of limb dynamics during arm reaching movements. We found evidence that corticospinal excitability is modulated in proportion to muscle activity and that the coefficients of proportionality vary in the course of these movements. Finally, further questions and future directions for this work are discussed in the Chapter 5

Muscle fatigue and other factors influencing forearm muscle activity

The wrist extensor muscles of the forearm exhibit relatively greater muscle activity than the wrist flexors during most hand/wrist tasks. Since the extensors operate at a greater percentage of maximum to balance wrist joint moments, this could contribute to their higher incidence of overuse injury. However, current knowledge of forearm muscle function comes primarily from isometric research or from studies examining isolated motor tasks. Conclusions derived from this work may not translate to tasks of daily living, which are typically dynamic and performed by multiple muscle actions simultaneously. Additionally, while fatigue develops more rapidly in the extensors than the flexors, the consequences of fatigue between these two muscle groups are presently unclear. The objectives of this thesis were broken into two parts. Part 1: Quantify forearm muscle recruitment during the simultaneous execution of various handgrip and wrist forces (Chapter 3) and during dynamic wrist exertions (Chapter 4). Part 2: Characterize the effects of sustained isometric wrist flexion and wrist extension contractions on hand-tracking accuracy (Chapter 5) and investigate the underlying central mechanisms that may contribute to accuracy impairments (Chapter 6). In Part 1, we identified that the muscle activity of the wrist flexors was highly sensitive to changes in dual-task parameters (grip and wrist exertions), while the activity of the extensors was consistently greater than the flexors during both dual-task and dynamic contractions. In some conditions, the wrist extensors exceeded flexor activity even during pure wrist flexion contractions. In Part 2, it was found that inducing fatigue separately through sustained wrist extension and wrist flexion contractions significantly impaired hand-tracking accuracy. However, there were no differences in hand-tracking accuracy between the two methods of inducing fatigue. This was surprising, given that follow-up work demonstrated both muscle activity and corticospinal differences between the muscle groups following sustained contractions. This thesis provides a robust examination of the factors that can influence forearm muscle recruitment. It is also the first work to document the consequences of fatigue in opposing muscle groups of the forearm. The conclusions drawn from this research are essential in furthering our understanding of overuse injury development in the distal upper-limb

Rehabilitation Outcome Following Acute Stroke: Considering Ideomotor Apraxia

Stroke is a leading cause of death and the leading cause of adult disability in the United States affecting approximately 795,000 people yearly. Stroke sequelae often span multiple domains, including motor, cognitive, and sensory subsystems. Impairments can contribute to difficulty participating in activities of daily living (ADLs) and translate into disability - a concern for patients and occupational therapists alike. The role of ideomotor apraxia (IMA) in stroke rehabilitation is unclear. Thus, the purpose of these two studies is to investigate stroke rehabilitation outcome while considering the presence of ideomotor apraxia. Stroke causes dysfunctional movement patterns arising from an array of potential etiologies. Agreement exists that understanding the patient's functioning serves as the basis for the rehabilitation process and it is insufficient for clinicians simply to determine functional movement problems without knowing how underlying impairments contribute. Stroke-induced paresis is a prevalent impairment and frequent target of traditional rehabilitation. Stroke rehabilitation often addresses paresis narrowly with little consideration for other stroke consequences. Ideomotor apraxia is one such disorder after stroke that could conceivably limit rehabilitation benefit of otherwise efficacious treatment interventions aimed at remediating paresis. This led us to an initial study of a subject who experienced a single left, ischemic stroke with paresis of his right upper extremity and comorbid ideomotor apraxia. The subject participated in combined physical and mental practice for six consecutive weeks to improve use of his right arm. After intervention, the subject demonstrated clinically significant improvements in functional performance of his more-affected right upper extremity and reported greater self-perception of performance. The subject continued to demonstrate improvements after four weeks with no intervention and despite persistent IMA. This single case report highlights the importance of recognizing that ideomotor apraxia does present after stroke, and traditional stroke rehabilitation efforts directed at paresis can be efficacious for subjects with IMA. Traditional beliefs suggested that ideomotor apraxia does not translate to disability in everyday life and that IMA resolves spontaneously. Despite accumulating evidence of the influence of IMA on functional ability, this topic remains relatively neglected. It is unclear how ideomotor apraxia affects the rehabilitation process. The second study reports rehabilitation outcomes of a group of subjects following acute stroke. The Florida Apraxia Battery gesture-to-verbal command test was used to detect IMA in subjects. Level of independence with a set of ADLs and motor impairment of the more-affected upper extremity was documented at admission and discharge. Study subjects participated in standard of care stroke rehabilitation in the inpatient rehabilitation units. A total of fifteen subjects who sustained a left hemisphere stroke participated in this study - ten with IMA and five without IMA. After rehabilitation, subjects with IMA improved ADL independence and displayed decreased motor impairment of their right upper extremity. Subjects with and without IMA exhibited comparable improvements in ADL independence, but subjects with IMA exhibited less ADL independence upon when compared to subjects without IMA. Additional findings suggested that subjects with IMA were not different with respect to motor impairments and length of stay; however, additional studies with larger sample sizes are needed. In summary, these two studies aid to elucidate the implications of ideomotor apraxia on traditional stroke rehabilitation efforts. Study subjects with ideomotor apraxia after acute stroke still derive benefit from traditional rehabilitation. Because traditional rehabilitation interventions narrowly target motor impairment, these findings support the need for considering IMA as a factor in developing interventions tailored to patients with IMA and possibly as a specific focus for interventions. A step toward addressing this need is to assess whether IMA is present after stroke on a regular basis. This work provides a framework for researchers and clinicians to investigate further how ideomotor apraxia translates into disability. These findings are important since consideration of ideomotor apraxia could influence selection and design of rehabilitation interventions to optimize patient daily functioning after stroke

Evaluation of Concavity Compression Mechanism as a Possible Predictor of Shoulder Muscle Fatigue

This study examined the lived experiences of American Muslim principals who serve in public schools post-9/11 to determine whether global events, political discourse, and the media coverage of Islam and Muslims have affected their leadership and spirituality. The aim of the study was to allow researchers and educators to gain an understanding of the adversities that American Muslims principals have experienced post-9/11 and to determine how to address these adversities, particularly through decisions about educational policy and district leadership. A total of 14 American Muslim school leaders who work in public schools post-9/11 across the United States participated in the study, and a phenomenological methodology was used to direct the data collection and coding. Edelman\u27s political spectacle theory served as the theoretical framework for the research. The findings yielded six themes of political climate, role of the media, inferior and foreign: being seen as the other, unconscious fear, spirituality, and education and communication over spectacle. Further, collective guilt and social responsibility emerged as two additional findings. The research suggests that political spectacle and its effects have a large impact on the lives of American Muslim principals, particularly in regard to their leadership and spirituality

Changes in the corticospinal excitability underlying voluntary wrist movement investigated with the TMS method

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal