Use of induced acceleration to quantify the (de)stabilization effect of external and internal forces on postural responses

Due to the mechanical coupling between the body segments, it is impossible to see with the naked eye the causes of body movements and understand the interaction between movements of different body parts. The goal of this paper is to investigate the use of induced acceleration analysis to reveal the causes of body movements. We derive the analytical equations to calculate induced accelerations and evaluate its potential to study human postural responses to support-surface translations. We measured the kinematic and kinetic responses of a subject to sudden forward and backward translations of a moving platform. The kinematic and kinetics served as input to the induced acceleration analyses. The induced accelerations showed explicitly that the platform acceleration and deceleration contributed to the destabilization and restabilization of standing balance, respectively. Furthermore, the joint torques, coriolis and centrifugal forces caused by swinging of the arms, contributed positively to stabilization of the center of mass. It is concluded that induced acceleration analyses is a valuable tool in understanding balance responses to different kinds of perturbations and may help to identify the causes of movement in different pathologies

Understanding motor control in humans to improve rehabilitation robots

Recent reviews highlighted the limited results of robotic rehabilitation and the low quality of evidences in this field. Despite the worldwide presence of several robotic infrastructures, there is still a lack of knowledge about the capabilities of robotic training effect on the neural control of movement. To fill this gap, a step back to motor neuroscience is needed: the understanding how the brain works in the generation of movements, how it adapts to changes and how it acquires new motor skills is fundamental. This is the rationale behind my PhD project and the contents of this thesis: all the studies included in fact examined changes in motor control due to different destabilizing conditions, ranging from external perturbations, to self-generated disturbances, to pathological conditions. Data on healthy and impaired adults have been collected and quantitative and objective information about kinematics, dynamics, performance and learning were obtained for the investigation of motor control and skill learning. Results on subjects with cervical dystonia show how important assessment is: possibly adequate treatments are missing because the physiological and pathological mechanisms underlying sensorimotor control are not routinely addressed in clinical practice. These results showed how sensory function is crucial for motor control. The relevance of proprioception in motor control and learning is evident also in a second study. This study, performed on healthy subjects, showed that stiffness control is associated with worse robustness to external perturbations and worse learning, which can be attributed to the lower sensitiveness while moving or co-activating. On the other hand, we found that the combination of higher reliance on proprioception with \u201cdisturbance training\u201d is able to lead to a better learning and better robustness. This is in line with recent findings showing that variability may facilitate learning and thus can be exploited for sensorimotor recovery. Based on these results, in a third study, we asked participants to use the more robust and efficient strategy in order to investigate the control policies used to reject disturbances. We found that control is non-linear and we associated this non-linearity with intermittent control. As the name says, intermittent control is characterized by open loop intervals, in which movements are not actively controlled. We exploited the intermittent control paradigm for other two modeling studies. In these studies we have shown how robust is this model, evaluating it in two complex situations, the coordination of two joints for postural balance and the coordination of two different balancing tasks. It is an intriguing issue, to be addressed in future studies, to consider how learning affects intermittency and how this can be exploited to enhance learning or recovery. The approach, that can exploit the results of this thesis, is the computational neurorehabilitation, which mathematically models the mechanisms underlying the rehabilitation process, with the aim of optimizing the individual treatment of patients. Integrating models of sensorimotor control during robotic neurorehabilitation, might lead to robots that are fully adaptable to the level of impairment of the patient and able to change their behavior accordingly to the patient\u2019s intention. This is one of the goals for the development of rehabilitation robotics and in particular of Wristbot, our robot for wrist rehabilitation: combining proper assessment and training protocols, based on motor control paradigms, will maximize robotic rehabilitation effects

Young, Healthy Subjects Can Reduce the Activity of Calf Muscles When Provided with EMG Biofeedback in Upright Stance

Recent evidence suggests the minimization of muscular effort rather than of the size of bodily sway may be the primary, nervous system goal when regulating the human, standing posture. Different programs have been proposed for balance training; none however has been focused on the activation of postural muscles during standing. In this study we investigated the possibility of minimizing the activation of the calf muscles during standing through biofeedback. By providing subjects with an audio signal that varied in amplitude and frequency with the amplitude of surface electromyograms (EMG) recorded from different regions of the gastrocnemius and soleus muscles, we expected them to be able to minimize the level of muscle activation during standing without increasing the excursion of the center of pressure (CoP). CoP data and surface EMG from gastrocnemii, soleus and tibialis anterior muscles were obtained from 10 healthy participants while standing at ease and while standing with EMG biofeedback. Four sensitivities were used to test subjects' responsiveness to the EMG biofeedback. Compared with standing at ease, the two most sensitive feedback conditions induced a decrease in plantar flexor activity (~15%; P < 0.05) and an increase in tibialis anterior EMG (~10%; P < 0.05). Furthermore, CoP mean position significantly shifted backward (~30 mm). In contrast, the use of less sensitive EMG biofeedback resulted in a significant decrease in EMG activity of ankle plantar flexors with a marginal increase in TA activity compared with standing at ease. These changes were not accompanied by greater CoP displacements or significant changes in mean CoP position. Key results revealed subjects were able to keep standing stability while reducing the activity of gastrocnemius and soleus without loading their tibialis anterior muscle when standing with EMG biofeedback. These results may therefore posit the basis for the development of training protocols aimed at assisting subjects in more efficiently controlling leg muscle activity during standing

Physiological Targets of Artificial Gravity: The Sensory-Motor System

This chapter describes the pros and cons of artificial gravity applications in relation to human sensory-motor functioning in space. Spaceflight creates a challenge for sensory-motor functions that depend on gravity, which include postural balance, locomotion, eye-hand coordination, and spatial orientation. The sensory systems, and in particular the vestibular system, must adapt to weightlessness on entering orbit, and again to normal gravity upon return to Earth. During this period of adaptation, which persists beyond the actual gravity-level transition itself the sensory-motor systems are disturbed. Although artificial gravity may prove to be beneficial for the musculoskeletal and cardiovascular systems, it may well have negative side effects for the neurovestibular system, such as spatial disorientation, malcoordination, and nausea

Traditional and Non-Traditional Inputs to the Vestibular System

One of the primary functions of the vestibular system is to provide stabilizing reflexes to the eye, head, and body. These reflexes are often coordinated with inputs from the visual and proprioceptive systems. More recently, research has shown that other, non-traditional, stimuli also affect the vestibular system, though the scope of this research has been limited. This thesis explores the effect of both traditional and non-traditional inputs on the vestibular system by characterizing their influence compensatory movements. We begin by looking at the influence of the vestibular periphery and efference copy on compensatory eye movements (Chapter 2). While each of these has been described individually (as the vestibular-ocular reflex (VOR) and pre-programmed eye movements (PPEM) respectively), there is currently controversy in the field regarding 1) to what extent PPEM influence gaze stabilization in healthy animals, and 2) how these two inputs interact with each other. We propose a model of gaze stability in which VOR and PPEM work cooperatively, and compare model predictions to our data as well as data others have reported. We found that our model accurately predicted eye movements for all behavioral contexts tested. In Chapter 3, we describe the effect of single high-intensity noise exposure on the vestibular system. Currently, controversy surrounds whether, and to what extent, noise damages the semi-circular canals. We characterized changes to both ocular and head stability to better answer this question and found that after noise exposure there was loss of both ocular and head stability. However, the exact nature of this deficit was not as expected and the influence of cervical pathways after vestibular lesion is discussed. Finally, in Chapter 4, we examine the effect of galvanic vestibular stimulation (GVS) and optokinetic stimulation on standing posture. We propose a model of postural stability inspired by the velocity storage model of ocular stability. While others have proposed more complex models that make similar predictions, those predictions have not been explicitly tested and, further, it’s not clear if the added complexity is necessary. We found that, while simple, our model could correctly predict subjects’ responses to both stimuli, suggesting that the body interprets and uses sensory information for postural stability in a manner similar to that for ocular stability. Taken together these findings demonstrate that the influence of non-traditional inputs and pathways to vestibular system is substantial and should be considered both in laboratory and clinical settings. Specifically, we showed in Chapter 2 that PPEM are not merely an enhanced or adapted VOR, but part of a unique gaze stabilization system that merits independent consideration. In Chapter 3, we showed that a single noise exposure can cause significant functional damage to the vestibular system, suggesting that patients with noise-induced hearing loss should be tested for vestibular loss as well. Finally, in Chapter 4, we showed that GVS can be integrated like natural vestibular stimulation but only if it is properly conditioned first. This is of particular importance for vestibular prosthetic design, which uses GVS to substitute for lost vestibular input.PHDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/143914/1/hastepha_1.pd

Fifteen years of wireless sensors for balance assessment in neurological disorders

Balance impairment is a major mechanism behind falling along with environmental hazards. Under physiological conditions, ageing leads to a progressive decline in balance control per se. Moreover, various neurological disorders further increase the risk of falls by deteriorating specific nervous system functions contributing to balance. Over the last 15 years, significant advancements in technology have provided wearable solutions for balance evaluation and the management of postural instability in patients with neurological disorders. This narrative review aims to address the topic of balance and wireless sensors in several neurological disorders, including Alzheimer's disease, Parkinson's disease, multiple sclerosis, stroke, and other neurodegenerative and acute clinical syndromes. The review discusses the physiological and pathophysiological bases of balance in neurological disorders as well as the traditional and innovative instruments currently available for balance assessment. The technical and clinical perspectives of wearable technologies, as well as current challenges in the field of teleneurology, are also examined

Effects of the use of occlusal splints on the neuromuscular function

Dispositivos orais, tais como as goteiras, têm sido promovidos como um meio para aumentar a performance desportiva. As goteiras promovem variações na posição do maxilar e como conseguinte criam alterações na articulação temporomandibular (ATM) e nos músculos masticatórios. Estudos têm sido feitos sobre os seus efeitos, a nível neuromuscular e fisiológico, para determinar as mudanças causadas pela sua utilização. Contudo, devido à escassez de estudos nesta área, bem como a lacunas nas metodologias usadas, não é possível dar uma resposta definitiva sobre a possível influência das goteiras na capacidade neuromuscular e na performance desportiva. Deste modo, o objetivo desta tese foi determinar os efeitos agudos da utilização de goteiras em diferentes aspetos da função neuromuscular. Para tal, cinco estudos foram realizados: 1) Uma revisão sistemática, que revelou evidências do efeito positivo das goteiras em tarefas isométricas do trem superior, para sujeitos destreinados; 2) Um estudo que demonstrou que as goteiras melhoram a força e atividade muscular em tarefas isocinéticas do trem superior, para sujeitos destreinados; 3) Um estudo que determinou que, em jogadores de rugby, as goteiras não aumentaram a força do trem superior num movimento balístico, mas com protetores bocais customizados aumentavam o pico de força e o pico de aceleração, embora outros parâmetros de força e potência não tenham sido afetados; 4) Um estudo que analisou a oscilação do corpo na marcha e corrida através da análise cinemática e não encontrou diferenças em função da utilização de goteiras; e 5) Um estudo que observou a oscilação do centro de pressão, a atividade EMG de músculos do membro superior e a precisão no alvo de atletas do tiro enquanto utilizavam goteiras e não encontrou diferenças em nenhum dos parâmetros. O efeito ergogénico das goteiras, ocorreu de forma clara em ações de força dinâmica do trem superior e em sujeitos destreinados. Protetores bocais customizados, que reposicionam em atletas treinados a ATM numa posição idêntica ás goteiras, melhoraram alguns parâmetros de força e aceleração em movimentos balísticos do trem superior, mas não afetaram outros parâmetros. Futuras investigações devem confirmar estas hipóteses, bem como averiguar o efeito a longo prazo da utilização de goteiras.Oral appliances, such as occlusal splints (OS), have been advocated as a mean to improve high-level sports performance. OS promote variations in jaw position and therefore create a change in the temporomandibular joint (TMJ) and on the masticatory muscles. They have been a subject of research, at neuromuscular and physiological level, to determined changes derived from the use of such devices. However, due to a paucity of research studies, and limitations on the used methods in the performed studies, it is not possible to give a correct and definite answer to the possible influence of OS on neuromuscular function and in the human sports performance. Therefore, this thesis aimed to ascertain the acute effects of occlusal splints on neuromuscular function. Five studies were conducted to achieve this purpose: 1) a systematic review, which revealed evidence of the effects of OS in upper body isometric tasks, for untrained healthy subjects; 2) a study that showed that OS enhance strength and muscle activity in upper body isokinetic tasks for untrained subjects; 3) a study which determined that for rugby athletes, OS did not increase strength in an upper body power movement, but a customized mouthguard increased peak force and peak acceleration despite other force and power did not change; 4) a study that analyzed kinematic body oscillation in gait and running and found no changes when using OS; and 5) a study that found no changes in body sway, EMG from upper limb muscles and shooting accuracy in pistol shooters while using OS. The ergogenic effect of OS was found in the dynamic strength performed by untrained subjects. Customized mouthguards, that reposition, for trained athletes, TMJ in an identical position as OS, increased some parameters of strength and acceleration but did not change other parameters. Future research should confirm these findings, while also determining the long-term effect of using OS

Biomechanical and neurophysiological mechanisms related to postural control and efficiency of movement: A review

Understanding postural control requires considering various mechanisms underlying a person's ability to stand, to walk, and to interact with the environment safely and efficiently. The purpose of this paper is to summarize the functional relation between biomechanical and neurophysiological perspectives related to postural control in both standing and walking based on movement efficiency. Evidence related to the biomechanical and neurophysiological mechanisms is explored as well as the role of proprioceptive input on postural and movement control.info:eu-repo/semantics/publishedVersio