Relationship Between Counter Movement Jump Performance and Extraversion Level

Introduction: Sport psychology literature has demonstrated a relationship between personality and physical ability and athletic performance. In general, individuals who exhibit a greater degree of extraversion display a greater physical ability and athletic performance than individuals who exhibit a lower degree of extraversion. The physiology literature has also demonstrated relationships between extraversion level and movement time and electrophysiological mechanisms (i.e., muscle activity) during a fine movement task. However to date, no study has investigated if these physiological relationships manifest themselves during a gross movement task. If a relationship exists, it may provide mechanistic reasoning behind the previously observed relationships between personality and physical ability and athletic performance. As such, the primary purpose of this study was to investigate the relationship between counter movement jump (CMJ) performance and personality. The secondary purpose was to investigate possible electrophysiological mechanisms (i.e., peak muscle activity) to further explain the relationship between CMJ performance and personality. Methods: This study examined the relationship between peak height, peak power output, peak force output, and peak velocity during the CMJ of 25 participants. Performance of the CMJ was examined through the use of a Myotest Sport unit. Peak muscle activity during the CMJ was also examined through the use of surface electromyography (EMG). EMG was utilized to determine if a relationship existed between extraversion level and agonist (quadriceps) and/or antagonist (hamstrings) muscle activity during the CMJ. All measures of personality were assessed via the Eysenck Personality Inventory (EPI). Bivariate Pearson correlations were used to examine the relationships among all tested variables. Results: Extraversion and neuroticism level were not significantly correlated to any of the CMJ performance measures. Extraversion level was not significantly correlated to any of the peak muscle activity in the right or left legs during the CMJ. Neuroticism level was only significantly related to peak muscle activity of the right semitendinosus (ST) during the CMJ. All other muscle activity correlations were not statistically significant. Conclusions: Personality does not appear to be significantly related to CMJ performance. However, a relationship between neuroticism level and peak muscle activity during the CMJ may exist, and further investigation is warranted

Assessment Of Neck And Shoulder Muscle Coactivations And The Effect On The Musculoskeletal System

Musculoskeletal disorders (MSDs) constitute one of the most important occupational health issues in healthcare workers who are susceptible to upper extremity disorders. Yet MSDs in the healthcare professions have not been studied extensively beyond the lower back. The focus population for this research is the field of dentistry where neck and shoulder disorders have been documented to have a high prevalence. Though quantitative data has been collected, many prior studies have focused on self-reported information. The goal of this research is to provide insight into the inter-relationship of muscles in the upper extremities. One way to accomplish this is to understand the muscle coactivation patterns in the neck and shoulders. A comprehensive profile of eleven superficial muscles is developed using electromyography (EMG): two in the neck (the sternocleidomastoid and upper trapezius), five that cross the shoulder joint (latissimus dorsi, infraspinatus, supraspinatus, anterior, lateral, and posterior deltoid, the pectoralis major), and two that stabilize the shoulder joint (triceps and biceps); providing objective and quantitative data. Multivariate multiple regression, correlation, the muscle coactivation indicator (MCI), and stochastic modeling, using conditional histograms, are used to better understand muscle coactivation patterns and muscle responses to independent variables. While the MCI showed relative coactivation level and correlation disclosed a dependency among dependent variables, regression was inconsistent in predicting muscle activity. Conditional histograms provided a means of coactivation assessment. Data gathered and knowledge gained is essential for the development of interventions to minimize MSDs and to understand muscle coactivation patterns in workers who maintain static postures

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

Motor patterns evaluation of people with neuromuscular disorders for biomechanical risk management and job integration/reintegration

Neurological diseases are now the most common pathological condition and the leading cause of disability, progressively worsening the quality of life of those affected. Because of their high prevalence, they are also a social issue, burdening both the national health service and the working environment. It is therefore crucial to be able to characterize altered motor patterns in order to develop appropriate rehabilitation treatments with the primary goal of restoring patients' daily lives and optimizing their working abilities. In this thesis, I present a collection of published scientific articles I co-authored as well as two in progress in which we looked for appropriate indices for characterizing motor patterns of people with neuromuscular disorders that could be used to plan rehabilitation and job accommodation programs. We used instrumentation for motion analysis and wearable inertial sensors to compute kinematic, kinetic and electromyographic indices. These indices proved to be a useful tool for not only developing and validating a clinical and ergonomic rehabilitation pathway, but also for designing more ergonomic prosthetic and orthotic devices and controlling collaborative robots

Analysis of the Interlimb similarity of motor patterns for improving stroke assessment and neurorehabilitation

Stroke is the leading cause of adult disability, with upper limb hemiparesis being one of the most common consequences. Regaining voluntary arm movement is one of the major goals of rehabilitation. However, even with intensive rehabilitation, approximately 30% of patients remain permanently disabled and only 5 to 20% of them recover full independence. Hence, there is an increasing interest in incorporating the latest advances in neuroscience, medicine and engineering to improve the efficacy of conventional therapies. In the last years, a variety of promising targets have been identified to improve rehabilitation. However, there is no consensus on which measure should be applied as a gold standard to study functional recovery. This fact dramatically hinders the development of new interventions since it turns difficult to compare different clinical trials and draw consistent conclusions about therapeutic efficiency. In addition, available scales are subjective, qualitative and often lead to incongruent outcomes. Indeed, there is increasing suspicion that the lack of optimal assessment measures hampers the detection of benefits of new therapies. Moreover, existing scales totally ignore the neuromuscular state of the patient masking the ongoing recovery processes. In consequence, making appropriate clinical decisions in such environment is almost impossible. In light of all these facts, the need for new objective biomarkers to develop effective therapies is undeniable. To give response to these demands we have organized this thesis into two main branches. On the one hand, we have developed an innovative physiological scale that reveals the neuromuscular state of the patient and is able to discriminate between motor impairment levels. The innovation here resides in the concept of interlimb similarity (ILS). Based on the latest findings about the modular organization of the motor system and taking into account that stroke provokes unilateral motor damage, we propose comparing the control structure of the unaffected arm with the control structure of the paretic arm to quantify motor impairment. We have defined the control structure as the set of muscle synergies and activation coefficients needed to complete a task. The advantage of this approach is not only its capacity to provide neuromuscular information about the patient, but also that the ILS is personalized to each patient and can purposely guide rehabilitation based on the patient¿s own physiological patterns. This supposes a huge advance taking into account the heterogeneity of stroke pathogenesis. On other hand, we have characterized the therapeutic potential of Visual Feedback (VF) as a tool to purposely induce neuroplastic changes. We have chosen VF among the various interventions proven to improve motor performance, because VF is a cheap strategy that can be implemented in almost any rehabilitation center. We demonstrate that VF is able to modulate the human control structure. In healthy subjects, it seems that VF makes accessible the refined dominant motor programs for the nondominant hemisphere giving rise to an increased interlimb similarity of the control structure. Interestingly, in stroke patients VF is able to manipulate the ILS of upper-limb kinematics in favor of finer motor control but a single training session seems not to be enough to fix those changes in the neuromuscular system of a damaged brain. Overall, these findings offer a new promising framework to develop and assess an effective intervention to guide the restoration of the original neuromuscular patterns and avoid unwanted maladaptive neuroplasticity. In conclusion, this thesis seeks moving forward in the understanding of human motor recovery processes and their relationship with neuroplasticity. In this sense, it provides important advances in the design of a new biomarker of motor impairment and tests the power of VF to modulate the neuromuscular control of patients with stroke.L'ictus és la principal causa de discapacitat en adults, essent l'hemiparèsia del membre superior una de les conseqüències més comunes. Els programes de rehabilitació tenen com a objectiu fonamental restituir la mobilitat del braç afectat. No obstant això, es calcula que només entre el 5 i el 20% dels pacients aconsegueixen recuperar la seva independència mentre que el 30% queden incapacitats permanentment. En front d'aquest escenari es fa necessari incorporar els últims avenços de la neurociència, la medicina i l'enginyeria en aquesta àrea. En els darrers anys s'han identificat diversos aspectes clau per intentar millorar la rehabilitació. El problema, però, és que no hi ha consens per definir una mesura com a "gold estàndard" per avaluar la recuperació funcional, motiu pel qual, el desenvolupament de noves teràpies queda profundament afectat, ja que esdevé impossible poder comparar diferents assajos clínics i extreure conclusions consistents sobre la seva eficiència terapèutica. A més, les diverses mesures que s'utilitzen són subjectives, qualitatives i sovint donen resultats incongruents. De fet, se sospita que la manca de mesures d'avaluació òptimes dificulta la detecció dels beneficis de noves teràpies. A tot això se li ha d'afegir que les mesures actuals no consideren l'estat neuromuscular del pacient, emmascarant els processos reparadors subjacents. Així doncs, prendre les decisions clíniques adequades sota aquestes condicions esdevé pràcticament impossible. En aquestes circumstàncies, no es pot ignorar el requeriment de nous biomarcadors que proporcionin dades objectives per catalitzar el disseny de teràpies efectives. Per donar resposta a aquesta situació, la tesi s'ha estructurat en dues parts. Per una banda, s'ha desenvolupat una innovadora escala fisiològica que revela l'estat neuromuscular del pacient i és capaç de discriminar entre diferents nivells d'incapacitat motora. La innovació rau en el concepte de similitud entre membres (ILS, en anglès). Així, basant-nos en els darrers descobriments sobre l'organització modular del sistema motor, i en el fet que l'ictus provoca dany unilateral, proposem comparar l'estructura de control del braç no-afectat amb l'estructura de control del braç parètic per quantificar la incapacitat motora. L'estructura de control l'hem definida com el conjunt de sinergies musculars i coeficients d'activació que es necessiten per a dur a terme una tasca. L'avantatge d'aquesta proposta és doble, ja que proporciona informació sobre l'estat neuromuscular del pacient i en ser personalitzable, pot guiar la rehabilitació d'acord amb els patrons fisiològics propis de cada pacient. Això suposa un enorme avenç en aquesta àrea, donada la immensa heterogeneïtat de la patogènesi d'aquest trastorn. D'altra banda, s'ha caracteritzat el potencial terapèutic del feedback visual (VF) per induir canvis neuroplàstics. Aquesta és una eina molt interessant perquè a més de millorar el control motor, és assequible per gairebé qualsevol centre de rehabilitació. S'ha demostrat que el VF és capaç de modular l'estructura de control. Concretament, el VF sembla transferir els programes motors de l'hemisferi dominant al costat no dominant augmentant així el ILS dels subjectes sans. En pacients amb ictus, el VF és capaç d'augmentar el ILS cinemàtic afavorint patrons de control més fins. En conclusió, l'objectiu d'aquesta tesi és aprofundir en la comprensió dels processos de recuperació motora i la seva relació amb la neuroplasticitat. La tesi ofereix un nou i prometedor marc per desenvolupar i avaluar procediments efectius per guiar la restauració dels patrons neuromusculars originals i evitar que el cervell pateixi canvis neuroplàstics indesitjables. Així, la tesi proporciona avanços importants en el disseny d'un biomarcador per quantificar la incapacitat motora i avaluar el potencial del VF per modular el control neuromuscular de pacients amb ictus.Postprint (published version

Analysis of the Interlimb similarity of motor patterns for improving stroke assessment and neurorehabilitation

Stroke is the leading cause of adult disability, with upper limb hemiparesis being one of the most common consequences. Regaining voluntary arm movement is one of the major goals of rehabilitation. However, even with intensive rehabilitation, approximately 30% of patients remain permanently disabled and only 5 to 20% of them recover full independence. Hence, there is an increasing interest in incorporating the latest advances in neuroscience, medicine and engineering to improve the efficacy of conventional therapies. In the last years, a variety of promising targets have been identified to improve rehabilitation. However, there is no consensus on which measure should be applied as a gold standard to study functional recovery. This fact dramatically hinders the development of new interventions since it turns difficult to compare different clinical trials and draw consistent conclusions about therapeutic efficiency. In addition, available scales are subjective, qualitative and often lead to incongruent outcomes. Indeed, there is increasing suspicion that the lack of optimal assessment measures hampers the detection of benefits of new therapies. Moreover, existing scales totally ignore the neuromuscular state of the patient masking the ongoing recovery processes. In consequence, making appropriate clinical decisions in such environment is almost impossible. In light of all these facts, the need for new objective biomarkers to develop effective therapies is undeniable. To give response to these demands we have organized this thesis into two main branches. On the one hand, we have developed an innovative physiological scale that reveals the neuromuscular state of the patient and is able to discriminate between motor impairment levels. The innovation here resides in the concept of interlimb similarity (ILS). Based on the latest findings about the modular organization of the motor system and taking into account that stroke provokes unilateral motor damage, we propose comparing the control structure of the unaffected arm with the control structure of the paretic arm to quantify motor impairment. We have defined the control structure as the set of muscle synergies and activation coefficients needed to complete a task. The advantage of this approach is not only its capacity to provide neuromuscular information about the patient, but also that the ILS is personalized to each patient and can purposely guide rehabilitation based on the patient¿s own physiological patterns. This supposes a huge advance taking into account the heterogeneity of stroke pathogenesis. On other hand, we have characterized the therapeutic potential of Visual Feedback (VF) as a tool to purposely induce neuroplastic changes. We have chosen VF among the various interventions proven to improve motor performance, because VF is a cheap strategy that can be implemented in almost any rehabilitation center. We demonstrate that VF is able to modulate the human control structure. In healthy subjects, it seems that VF makes accessible the refined dominant motor programs for the nondominant hemisphere giving rise to an increased interlimb similarity of the control structure. Interestingly, in stroke patients VF is able to manipulate the ILS of upper-limb kinematics in favor of finer motor control but a single training session seems not to be enough to fix those changes in the neuromuscular system of a damaged brain. Overall, these findings offer a new promising framework to develop and assess an effective intervention to guide the restoration of the original neuromuscular patterns and avoid unwanted maladaptive neuroplasticity. In conclusion, this thesis seeks moving forward in the understanding of human motor recovery processes and their relationship with neuroplasticity. In this sense, it provides important advances in the design of a new biomarker of motor impairment and tests the power of VF to modulate the neuromuscular control of patients with stroke.L'ictus és la principal causa de discapacitat en adults, essent l'hemiparèsia del membre superior una de les conseqüències més comunes. Els programes de rehabilitació tenen com a objectiu fonamental restituir la mobilitat del braç afectat. No obstant això, es calcula que només entre el 5 i el 20% dels pacients aconsegueixen recuperar la seva independència mentre que el 30% queden incapacitats permanentment. En front d'aquest escenari es fa necessari incorporar els últims avenços de la neurociència, la medicina i l'enginyeria en aquesta àrea. En els darrers anys s'han identificat diversos aspectes clau per intentar millorar la rehabilitació. El problema, però, és que no hi ha consens per definir una mesura com a "gold estàndard" per avaluar la recuperació funcional, motiu pel qual, el desenvolupament de noves teràpies queda profundament afectat, ja que esdevé impossible poder comparar diferents assajos clínics i extreure conclusions consistents sobre la seva eficiència terapèutica. A més, les diverses mesures que s'utilitzen són subjectives, qualitatives i sovint donen resultats incongruents. De fet, se sospita que la manca de mesures d'avaluació òptimes dificulta la detecció dels beneficis de noves teràpies. A tot això se li ha d'afegir que les mesures actuals no consideren l'estat neuromuscular del pacient, emmascarant els processos reparadors subjacents. Així doncs, prendre les decisions clíniques adequades sota aquestes condicions esdevé pràcticament impossible. En aquestes circumstàncies, no es pot ignorar el requeriment de nous biomarcadors que proporcionin dades objectives per catalitzar el disseny de teràpies efectives. Per donar resposta a aquesta situació, la tesi s'ha estructurat en dues parts. Per una banda, s'ha desenvolupat una innovadora escala fisiològica que revela l'estat neuromuscular del pacient i és capaç de discriminar entre diferents nivells d'incapacitat motora. La innovació rau en el concepte de similitud entre membres (ILS, en anglès). Així, basant-nos en els darrers descobriments sobre l'organització modular del sistema motor, i en el fet que l'ictus provoca dany unilateral, proposem comparar l'estructura de control del braç no-afectat amb l'estructura de control del braç parètic per quantificar la incapacitat motora. L'estructura de control l'hem definida com el conjunt de sinergies musculars i coeficients d'activació que es necessiten per a dur a terme una tasca. L'avantatge d'aquesta proposta és doble, ja que proporciona informació sobre l'estat neuromuscular del pacient i en ser personalitzable, pot guiar la rehabilitació d'acord amb els patrons fisiològics propis de cada pacient. Això suposa un enorme avenç en aquesta àrea, donada la immensa heterogeneïtat de la patogènesi d'aquest trastorn. D'altra banda, s'ha caracteritzat el potencial terapèutic del feedback visual (VF) per induir canvis neuroplàstics. Aquesta és una eina molt interessant perquè a més de millorar el control motor, és assequible per gairebé qualsevol centre de rehabilitació. S'ha demostrat que el VF és capaç de modular l'estructura de control. Concretament, el VF sembla transferir els programes motors de l'hemisferi dominant al costat no dominant augmentant així el ILS dels subjectes sans. En pacients amb ictus, el VF és capaç d'augmentar el ILS cinemàtic afavorint patrons de control més fins. En conclusió, l'objectiu d'aquesta tesi és aprofundir en la comprensió dels processos de recuperació motora i la seva relació amb la neuroplasticitat. La tesi ofereix un nou i prometedor marc per desenvolupar i avaluar procediments efectius per guiar la restauració dels patrons neuromusculars originals i evitar que el cervell pateixi canvis neuroplàstics indesitjables. Així, la tesi proporciona avanços importants en el disseny d'un biomarcador per quantificar la incapacitat motora i avaluar el potencial del VF per modular el control neuromuscular de pacients amb ictus

Neuromuscular Function Following Lengthening Contractions

Unaccustomed lengthening contractions have been shown to impair muscle function - however little is known regarding this impairment on muscle power - specifically, the velocity component of power during voluntary contractions in humans. The four studies presented in my thesis investigated power-loss following lengthening contractions in healthy young and old women and young men. The purpose of Study 1 was to determine reliability of velocity-dependent power of the dorsiflexors using the isotonic mode of the Biodex Dynamometer. I determined the isotonic mode is reliable and can be used to track changes in velocity and power following fatigue and lengthening contractions. The purpose of Study 2 was to investigate changes in neuromuscular properties of the ankle dorsiflexors during and following repetitive lengthening contractions and throughout recovery in 21 (10 men, and, 11 women) recreationally active young adults (25.8 ± 2.3 y). The protocol for the following 3 studies involves subjects performing 5 sets of 30 lengthening contractions, with neuromuscular measures (i.e., electrically evoked twitch, tetanus, voluntary activation, voluntary contractions) recorded at baseline, during the task, and throughout recovery. Exercise induced muscle damage ultimately led to velocity-dependent (i.e., isotonic) power loss at a moderate load (i.e., 20% maximum voluntary strength). Compared with isometric and isokinetic tasks, less is known regarding velocity-dependent muscle power and recovery in older adults following repeated lengthening contractions. In Study 3 we tested 9 old (68.3 ± 6.1 y) and 9 young women (25.1 ± 1.3 y). Old were more impaired following the task than young as shown by greater low-frequency torque depression at task termination leading to a more pronounced initial loss of power than young. However, power remained reduced in both groups during the 30 min recovery period. Older women were more susceptible to power loss than young following lengthening contractions likely owing to a greater fatigue response. In Study 4, power curves were constructed [8 men (27 ± 3 y), 8 women (26 ± 4 y)] using various isotonic loads before and following task termination. There was a preferential loss of power at higher loads, with a relative maintenance of maximal shortening velocity shifting the power curve down and leftward. When stressed with heavier loads during dynamic contractions, force modulators arranged in parallel seem to be affected more by damage than those organized in series (velocity), which was highlighted by the attenuation of power at higher versus lower resistances. The main findings of my thesis are that repetitive lengthening contractions fatigued and temporarily weakened the dorsiflexors, thus impairing their power producing ability immediately (i.e., fatigue + weakness) and longer term (i.e., weakness) owing to an inability to generate torque rapidly

The relationship between perception of effort and physiological responses to an acute fatiguing task of the elbow flexors. Evaluation of a new rating scale of perception of effort

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.While fatigue is a common daily phenomenon, the exact relationship between perception of effort and fatigue is still unknown. Existing tools for assessing perception of effort are effectively limited to whole body exercise, while current methods for assessing voluntary activation are painful and not feasible for clinical application. The main aims of this thesis were to evaluate existing methodologies for their appropriateness in assessing perception of effort and voluntary activation following isolated muscle function testing, and to examine the relationship between subjective perception of effort and objective changes in the healthy motor control system. The implementation of reliable and valid assessment tools in clinical practice may enable clarification of the pathogenesis of many neurological conditions that have chronic fatigue as a key feature. Four studies of within-subjects repeated measures design have been conducted. Sixtynine healthy volunteers were recruited among staff and students of Brunel University. Magnetic stimulation was tested as a valid alternative to electrical stimulation in the conventional single-pulse Twitch Interpolation Technique. The 0–10 Numeric Rating Scale (NRS) was also tested for its reliability and validity in assessing the perception of effort during isometric exercise of elbow flexors. The changes of perception of effort following a submaximal elbow flexion fatiguing task, as well as following transcranial direct current stimulation (tDCS) over the motor cortex were also tested. The main findings showed significant differences between peripheral and magnetic stimulation in conventional single-pulse Twitch Interpolation Technique. The 0–10 NRS demonstrated linear properties and reported excellent test-retest reliability and good concurrent criterion validity in recording perception of effort under repeated isometric contractions of elbow flexors. Ten minutes of a submaximal intermittent isometric fatiguing exercise produced a significant elevation in rating of perceived effort, which was associated with central and peripheral neurophysiological changes of the motor control system. In contrast, perception of effort did not change significantly following 10 minutes of tDCS. The major findings of this thesis suggest the 0–10 NRS is a valid and reliable scale for rating perception of effort in healthy individuals. Further testing of the scale on patients is needed to establish its validity in clinical settings. Additionally, the findings indicate a substantial role of perception of effort in the voluntary motor control system. However, further research towards revealing the underlying mechanisms of perceived effort regulation in both health and disease is required

Neuromuscular mechanisms underlying changes in force production during an attentional focus task

The objective of this thesis was to examine changes in maximal voluntary force output of the elbow flexors with attentional focus feedback cues and possible underlying physiological mechanisms for these changes. Eleven recreationally active males participated in two randomized experimental sessions (Day 1: n=11, Day 2: n=10); 1) Stimulation session where corticospinal excitability was measured and 2) No stimulation session where only electromyography and elbow flexor force was measured. In both sessions, four randomized blocks of three maximal voluntary contractions (MVC) were performed. Each block consisted of either externally or internally attentional focus cues given before each MVC. During the stimulation session transcranial magnetic, transmastoid and Erb’s point stimulations were used to induce motor evoked potentials (MEPs), cervicomedullary MEP (CMEPs) and maximal muscle action potential (Mmax). All MEPs and CMEPs were normalized to Mmax. Results showed participants could produce greater MVC force without stimulation and given an external focus cue before the MVC compared to an internal cue. Muscle co-activation data (expressed as % triceps/biceps rmsEMG) during the no stimulation session was greater with internally cued compared to externally cued contractions. There was no difference in corticospinal excitability shown between external and internal focus cues in the stimulation session. In conclusion, maximal voluntary force production of the elbow flexors was greater when an external focus feedback cue was provided. This appeared to be due to less coactivation of the triceps and biceps brachii. Secondly, stimulating the corticospinal pathway seemed to have some confounding effect on attentional focus. The distressing stimulations distracted participants from attentional focus cued feedback or stimulating the corticospinal pathway may have disrupted areas of the cortex responsible for attention and focus

Submaximal Isometric Force Steadiness in People with Multiple Sclerosis Under Single and Dual Task Conditions

Activities of daily living require steady, non-fatiguing, isometric muscular contractions to maintain postural control and stabilize body segments to facilitate interaction with the environment. Furthermore, typical activities often require simultaneous performance of cognitive and motor tasks. This may challenge people with multiple sclerosis, a chronic neurodegenerative disease of the central nervous system associated with motor and cognitive impairments. Despite functional relevance, isometric force steadiness in both the upper and lower extremities has not been explored in this population. Additionally, dual task experiments in multiple sclerosis have primarily used gait, a dynamic activity, as the motor task. Thus, the purpose of this dissertation was to examine isometric force steadiness performed under single and dual task conditions in people with multiple sclerosis. It was hypothesized that people with multiple sclerosis would be less steady and have greater dual task costs of cognitive-motor tasks.Study one measured steadiness of the ankle dorsiflexors and elbow flexors across a range of low to moderate force targets during a single task condition. Absolute force fluctuation at each target was measured and relative fluctuation was calculated using the coefficient of variation. In the elbow flexors, people with multiple sclerosis were less steady than controls only at very low forces and were less steady at nearly all force targets in the ankle. However, magnitudes of upper and lower extremity force fluctuation did not correlate within either sample.Study two determined dual task effects of simultaneous performance of a steady ankle dorsiflexion contraction and a cognitive task involving working memory and processing speed. Both controls and people with multiple sclerosis experienced negative dual task effects on motor and cognitive performances. Although those with multiple sclerosis did not perform as well as controls for all tasks, there was no difference in motor effects.This dissertation shows that 1.) isometric steadiness is impaired in the upper and lower extremities of people with multiple sclerosis at very low forces under single task conditions, 2.) people with multiple sclerosis experience cognitive-motor interference when dual tasking, and 3.) the relative dual task motor effects are nonetheless comparable to what is experienced by healthy controls