Effects of varying force levels and combinations of force application and release during an isometric pinch force task

Fine motor control is important for the completion of many activities of daily living, such as writing, eating, buttoning a shirt, and texting. All these tasks require a high amount of continuous coordination and regulation of increasing and decreasing forces between multiple digits using sub-maximal force levels to successfully accomplish the task. Thus understanding the coordination of force regulation by the thumb and index finger at these sub-maximal force levels is a relevant topic especially for rehabilitation and instrumentation. This study was designed to investigate how accuracy and smoothness of performance of an isometric pinch force tracking task is affected by changing the level of forces required to perform the task and by different combinations of application and release of force by the thumb and index finger. Twenty two healthy, right handed adult participants between the ages of 18-30 were asked to manipulate a cursor to track a moving target ball counterclockwise around a prescribed path using the thumb and index finger of the right hand only. The goal of the task was to keep the cursor as close as possible to the moving target throughout the entire trial. Each participant was given 50 practice trials: 25 at 24% MVC and 25 at 12% MVC. For the 40 experimental trials, participants returned 24 hours later to complete 10 trials at each of the following force levels: 4%, 8%, 16%, and 32%. RMSE and CVE were calculated for each digit (thumb and index finger) as well as the combined digits and were used as indicators of accuracy and smoothness, respectively. Results showed significant differences in all dependent variables with p-values less than 0.05. Task performance accuracy was found to decrease as force level increased, whereas smoothness was found to decrease as force level decreased for all three. These findings suggest that varying force levels and combinations of force application and force release can change performance of this fine motor task and should be further investigated in order to better understand mechanisms involved and for implementing new designs of equipment and diagnostic tools.Kinesiology and Health Educatio

Aging, Neuromuscular Decline, and the Change in Physiological and Behavioral Complexity of Upper-Limb Movement Dynamics

Aging is characterized by a general decline in physiological and behavioral function that has been widely interpreted within the context of the loss of complexity hypothesis. In this paper, we examine the relation between aging, neuromuscular function and physiological-behavioral complexity in the arm-hand effector system, specifically with reference to physiological tremor and isometric force production. Experimental findings reveal that the adaptive behavioral consequences of the aging-related functional decline in neurophysiological processes are less pronounced in simple motor tasks which provides support for the proposition that the motor output is influenced by both extrinsic (e.g., task related) and intrinsic (e.g., coordination, weakness) factors. Moreover, the aging-related change in complexity can be bidirectional (increase or decrease) according to the influence of task constraints on the adaptation required of the intrinsic properties of the effector system

Age and Practice Effects on Inter-Manual Performance Asymmetry

Manual dexterity declines with increasing age, however, the way in which inter-manual asymmetry responds to aging is unclear. Our purpose was to determine the effect of age and practice on inter-manual performance asymmetry in an isometric force pinch line tracing task that varied in difficulty within segments. Thirty right-handed participants, five males and five females in each of three age groups, young (Y20), young–old (O70), and old–old (O80), practiced an isometric force pinch task for 10 trials with each hand on each of five consecutive days. Inter-manual performance asymmetry of the right and left hands was analyzed with a repeated measures analysis of variance (ANOVA) of asymmetry with age groups, practice, task difficulty, and hand as factors. The within-individual magnitude of asymmetry was also analyzed with a repeated measures ANOVA of manual asymmetry calculated as an asymmetry index (AI). Post hoc pair-wise comparisons were performed when significance was found. We observed no inter-manual performance asymmetry on this isometric tracing task among any of the age groups, either in the hand performance differences or in the magnitude of the AI. Age and practice interacted in terms of manual performance: the Y20 and O70 group improved accuracy and task time across the 5 days of practice but the O80 group did not. However, practice did not differentially affect the AI for accuracy or task time for any group. Accuracy of performance of the two hands was differentially affected by practice. All age groups exhibited poorer performance and larger AIs on the most difficult segments of the task (3 and 6) and this did not change with practice

MOTOR CONTROL OF THUMB-INDEX SYSTEM IN HEALTHY POPULATION

Thumb and Index fingers are involved in many daily tasks, it is understandable how injuries, musculoskeletal, rheumatologic, and neurological diseases could affect hand function causing severe disability. The evaluation of motor control deficits of the thumb-index system is necessary to identify impairments and to propose specific therapeutic or surgical proposes. Pinch maximal voluntary contraction is the most investigated parameter, it is a valid estimator of general hand function. However, thumb and index are rarely involved at their maximal contraction, usually they are used in precision pinches at low submaximal forces exerted for a short-to-long time. For this reason other parameters must be investigated. In this dissertation, a multiparametric evaluation of thumb-index system was proposed. The battery of tests consisted of the maximal voluntary contraction (MVC) of pinch grip (TP, tip pinch and PP, palmar pinch) and of the opposite movement (E, extension of thumb and index), the endurance (SC, sustained contraction), the accuracy and precision of pinch force in a pinch and release task (DC, dynamic contraction) and the force coordination between hands in a bimanual simultaneous task (BSC, bimanual strength coordination). The tasks were measured with a measurement system consisted of two pinch gauges, connected to a PC, the visual feedback was displayed on a monitor through the graphical user interface of an ad-hoc developed software. To be usable in the clinical context, it is important to check the reliability of the tasks and collecting data in healthy samples permits on the one hand to analyse how values changes as function of anthropometric variables, hand dominance, dexterity, and on the other hand to define the reference values to compare pathological populations. Therefore this dissertation was conducted through test-retest reliability studies and cross-sectional studies to establish normative data of PP, TP, E MVCs, SC, DC and BSC in the Italian population. All the tasks proved reliable and consistent, MVC and SC showed high reliability, DC and BSC reliability was lower but clinically suitable. Strength, analysed through PP, TP, E MVCs, declined in line with the normal process of aging that also entails muscle fibers and the reduction of daily activities in older adults. In relative terms, E-MVC showed the highest strength loss in the over 75y. SC showed similar values in all age groups, variables of DC and BSC showed instead large effect related to age-decline. Women performed better than men only in SC, in MVC, DC and BSC men excelled. A hand dominance effect emerged only in TP and PP MVC. Correlations between tasks were very low to low, suggesting that different constructs were measured by the tasks. This Ph.D. project proposed novel tasks to evaluate pinch motor control which were showed reliable in healthy people and their normative data were obtained, representing a useful aid in the clinical field. The results become a starting point for future studies to highlight impairments of the thumb-index system in different neurological and musculoskeletal disorders and to guide the rehabilitation and the therapeutic intervention

Avaliação dos efeitos da estimulação vibrotátil senoidal no controle neurofisiológico da força muscular

Orientador: Leonardo Abdala EliasTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: A realimentação das vias sensoriais periféricas é de suma importância, não apenas para a percepção sensorial, mas também para o controle neural dos movimentos voluntários. As aferentes cutâneas são responsáveis por uma ampla gama de sensações de toque e têm um papel crucial na modulação do comportamento motor. Um interessante efeito induzido pela estimulação dos mecanorreceptores cutâneos é a melhora do desempenho sensório-motor. O efeito benéfico da estimulação vibrotátil é atribuído à ocorrência de ressonância estocástica no sistema nervoso. A hipótese principal é que uma intensidade específica do estímulo vibrotátil aumentaria o influxo das aferentes, melhorando assim a integração sensório-motora no sistema nervoso central. Neste trabalho, pretendemos avaliar os efeitos de uma estimulação vibrotátil senoidal no controle neurofisiológico da força muscular. Primeiramente, exploramos os efeitos da estimulação vibrotátil senoidal na variabilidade da força muscular durante tarefas visuomotoras isométricas. Ademais, avaliamos a influência da intensidade de contração e lateralidade na melhora motora causada pela estimulação vibrotátil. Por fim, avaliamos as propriedades de disparos de uma população de unidades motoras registradas durante uma tarefa motora aprimorada pela estimulação vibrotátil. No final deste material, forneceremos novas interpretações dos mecanismos neurofisiológicos por trás da influência das aferentes sensoriais cutâneas no controle da força muscularAbstract: Peripheral feedback is of paramount importance not only for sensory perception but also for the neural control of voluntary movements. Cutaneous afferents are responsible for a wide range of touch sensation and have a crucial role in modulating motor behavior. An exciting effect induced by the stimulation of mechanoreceptors at the skin is the improvement of sensorimotor performance. The beneficial effect of vibrotactile stimulation is attributed to the occurrence of stochastic resonance in the nervous system. The central hypothesis is that a specific intensity of vibrotactile stimulus would increase the afferent inflow, thereby improving the sensorimotor integration in the central nervous system. In this work, we aim at evaluating the effects of a sinusoidal vibrotactile stimulation on the neurophysiological control of muscle force. We first explored the effects of sinusoidal vibrotactile stimulation on force steadiness during isometric visuomotor tasks. We further evaluated the influence of contraction intensity and handedness on the motor improvement caused by vibrotactile stimulation. Finally, we evaluated the firing properties of a population of motor units recorded during a motor-enhanced task. At the end of this material, we will provide novel interpretations on the neurophysiological mechanisms behind the influence of cutaneous sensory inputs on muscle force controlDoutoradoEngenharia BiomédicaDoutora em Engenharia Elétrica88881.134842/2016-01CAPE

MULTI-DIGIT HUMAN PREHENSION

The current dissertation addresses the central nervous system (CNS) strategies to solve kinetic redundancy in multi-digit static prehension under different geometries of hand-held objects and systematically varied mechanical constraints such as translation and rotation of the hand-held object. A series of experiments conducted for this dissertation tested the following hypotheses suggested in the current literatures for multi-digit human static prehension: Hierarchical organization hypothesis, principle of superposition hypothesis, proximity hypothesis, and mechanical advantage hypothesis. (1) Forces and moments produced by fingers during circular object prehension were grouped into two independent subsets: one subset related to grasping stability control and the other associated with rotational equilibrium control. This result supports the principle of superposition hypothesis. Individual fingers acted synergistically to compensate each other's errors. This result confirms the hierarchical organization hypothesis in circular object prehension. (2) During fixed object prehension of a rectangular object, the closer the non-task fingers positioned to the task finger, the greater the forces produced by the non-task fingers. However, during free object prehension, the non-task fingers with longer moment arms produced greater forces. The former and latter results support the proximity hypothesis and the mechanical advantage hypothesis, respectively. (3) The grasping stability control and rotational equilibrium control were decoupled during fixed object prehension as well as free object prehension. This result supports the principle of superposition hypothesis regardless of the mechanical constraints provided for these two prehension types. (4) During torque production, the fingers with longer moment arms produced greater forces when the fingers acted as agonists for the torque production. Therefore, the mechanical advantage hypothesis was supported for agonist fingers. (5) Coupling of thumb normal force and virtual finger normal force was not necessitated when horizontal translation of hand-held object was mechanically fixed. However, the coupling of two normal forces was always observed regardless of given translational constraints, and these two normal forces were independent to other mechanical variables such as tangential forces and moments. This result supports the principle of superposition hypothesis in static prehension under varied combinations of translational constraints

Clinical Decision Support Systems with Game-based Environments, Monitoring Symptoms of Parkinson’s Disease with Exergames

Parkinson’s Disease (PD) is a malady caused by progressive neuronal degeneration, deriving in several physical and cognitive symptoms that worsen with time. Like many other chronic diseases, it requires constant monitoring to perform medication and therapeutic adjustments. This is due to the significant variability in PD symptomatology and progress between patients. At the moment, this monitoring requires substantial participation from caregivers and numerous clinic visits. Personal diaries and questionnaires are used as data sources for medication and therapeutic adjustments. The subjectivity in these data sources leads to suboptimal clinical decisions. Therefore, more objective data sources are required to better monitor the progress of individual PD patients. A potential contribution towards more objective monitoring of PD is clinical decision support systems. These systems employ sensors and classification techniques to provide caregivers with objective information for their decision-making. This leads to more objective assessments of patient improvement or deterioration, resulting in better adjusted medication and therapeutic plans. Hereby, the need to encourage patients to actively and regularly provide data for remote monitoring remains a significant challenge. To address this challenge, the goal of this thesis is to combine clinical decision support systems with game-based environments. More specifically, serious games in the form of exergames, active video games that involve physical exercise, shall be used to deliver objective data for PD monitoring and therapy. Exergames increase engagement while combining physical and cognitive tasks. This combination, known as dual-tasking, has been proven to improve rehabilitation outcomes in PD: recent randomized clinical trials on exergame-based rehabilitation in PD show improvements in clinical outcomes that are equal or superior to those of traditional rehabilitation. In this thesis, we present an exergame-based clinical decision support system model to monitor symptoms of PD. This model provides both objective information on PD symptoms and an engaging environment for the patients. The model is elaborated, prototypically implemented and validated in the context of two of the most prominent symptoms of PD: (1) balance and gait, as well as (2) hand tremor and slowness of movement (bradykinesia). While balance and gait affections increase the risk of falling, hand tremors and bradykinesia affect hand dexterity. We employ Wii Balance Boards and Leap Motion sensors, and digitalize aspects of current clinical standards used to assess PD symptoms. In addition, we present two dual-tasking exergames: PDDanceCity for balance and gait, and PDPuzzleTable for tremor and bradykinesia. We evaluate the capability of our system for assessing the risk of falling and the severity of tremor in comparison with clinical standards. We also explore the statistical significance and effect size of the data we collect from PD patients and healthy controls. We demonstrate that the presented approach can predict an increased risk of falling and estimate tremor severity. Also, the target population shows a good acceptance of PDDanceCity and PDPuzzleTable. In summary, our results indicate a clear feasibility to implement this system for PD. Nevertheless, long-term randomized clinical trials are required to evaluate the potential of PDDanceCity and PDPuzzleTable for physical and cognitive rehabilitation effects

Cortico-muscular coherence in sensorimotor synchronisation

This thesis sets out to investigate the neuro-muscular control mechanisms underlying the ubiquitous phenomenon of sensorimotor synchronisation (SMS). SMS is the coordination of movement to external rhythms, and is commonly observed in everyday life. A large body of research addresses the processes underlying SMS at the levels of behaviour and brain. Comparatively, little is known about the coupling between neural and behavioural processes, i.e. neuro-muscular processes. Here, the neuro-muscular processes underlying SMS were investigated in the form of cortico-muscular coherence measured based on Electroencephalography (EEG) and Electromyography (EMG) recorded in human healthy participants. These neuro-muscular processes were investigated at three levels of engagement: passive listening and observation of rhythms in the environment, imagined SMS, and executed SMS, which resulted in the testing of three hypotheses: (i) Rhythms in the environment, such as music, spontaneously modulate cortico-muscular coupling, (ii) Movement intention modulates cortico-muscular coupling, and (iii) Cortico-muscular coupling is dynamically modulated during SMS time-locked to the stimulus rhythm. These three hypotheses were tested through two studies that used Electroencephalography (EEG) and Electromyography (EMG) recordings to measure Cortico-muscular coherence (CMC). First, CMC was tested during passive music listening, to test whether temporal and spectral properties of music stimuli known to induce groove, i.e., the subjective experience of wanting to move, can spontaneously modulate the overall strength of the communication between the brain and the muscles. Second, imagined and executed movement synchronisation was used to investigate the role of movement intention and dynamics on CMC. The two studies indicate that both top-down, and somatosensory and/or proprioceptive processes modulate CMC during SMS tasks. Although CMC dynamics might be linked to movement dynamics, no direct correlation between movement performance and CMC was found. Furthermore, purely passive auditory or visual rhythmic stimulation did not affect CMC. Together, these findings thus indicate that movement intention and active engagement with rhythms in the environment might be critical in modulating CMC. Further investigations of the mechanisms and function of CMC are necessary, as they could have important implications for clinical and elderly populations, as well as athletes, where optimisation of motor control is necessary to compensate for impaired movement or to achieve elite performance

Electromyographic, mechanomyographic, and peak torque responses during repeated concentric isokinetic muscle actions with eyes-open versus eyes-closed

The purpose of this study was to compare the peak torque and electromyographic (EMG) and mechanomyographic (MMG) amplitude and mean frequency (MNF) responses during fatiguing isokinetic muscle actions for eyes-open versus eyes-closed conditions. Twenty-one resistance-trained men (mean ± SD age = 23.0 ± 3.0 years; body mass = 86.9 ± 14.4 kg) volunteered to participate in this investigation. Following a familiarization session, each subject participated in four data collection trials. For each trial, the subjects performed 100 repeated maximal concentric isokinetic muscle actions of the dominant forearm flexors with 1) their eyes open (100Open), 2) their eyes closed (100Closed), 3) their eyes open and closed for the first and last 50 muscle actions (50Open50Closed), respectively, and 4) their eyes closed and open for the first and last 50 muscle actions (50Closed50Open), respectively. During each muscle action, EMG and MMG signals were detected from the biceps brachii. For each fatigue test, the data for the first and last 50 muscle actions served as the pre-test (Pre) and post-test (Post), respectively, and were compared for each condition. Initial peak torque (average from the three repetitions with the highest peak torque values), final peak torque (average from the three repetitions with the lowest peak torque values), percent decline ([initial peak torque - final peak torque/initial peak torque] × 100), average torque (average peak torque value across the 50 repetitions), and the linear slope coefficient for the decline in peak torque (ft.-lbs./repetition) were the five isokinetic peak torque variables in this study. In addition, for each subject and condition, the normalized EMG and MMG amplitude and MNF data points at initial and final peak torque were averaged and utilized for subsequent statistical analyses. The results indicated that there were no mean differences among the conditions for the five isokinetic peak torque variables. The mean normalized EMG MNF values at final peak torque decreased from Pre to Post for 100Open and 50Closed50Open conditions, but not for the eyes-closed conditions (i.e., 100Closed and 50Open50Closed). For the 100Open and 100Closed conditions, there were no Pre versus Post mean differences for normalized MMG MNF at final peak torque. When the subjects opened (50Closed50Open) and closed (50Open50Closed) their eyes after 50 repetitions, however, the normalized MMG MNF values continued to decrease. These findings suggested that visual feedback did not influence maximal strength or fatigability, but did affect EMG and MMG MNF