Range-based techniques for discovering optimality and analyzing scaling relationships in neuromechanical systems

In this paper, a method for decoupling the neuromuscular function of a set of limbs from the role morphology plays in regulating the performance of an activity is introduced. This method is based on two previous methods: the rescaled range analysis specific to time series data, and the use of scaling laws. A review of the literature suggests that limb geometry can either facilitate or constrain performance as measured experimentally. Whether limb geometry is facilitatory or acts as a constraint depends on the size differential between arm morphology and the underlying muscle. "Changes in size and shape" are theoretically extrapolations of morphological geometry to other members of a population or species, to other species, or to technological manipulations of an individual via prosthetic devices. Three datasets are analyzed using the range-based method and a Monte-Carlo simulation, and are used to test the various ways of executing this analysis. It was found that when performance is kept stable but limb size and shape is scaled by a factor of .25, the greatest gain in performance results. It was also found that introducing force-based perturbations results in 'shifts' in the body geometry/performance relationship. While results such as this could be interpreted as a statistical artifact, the non-linear rise within a measurement class and linear decrease between measurement classes suggests an effect of scale in the optimality of this relationship. Overall, range-based techniques allow for the simulation and modeling of myriad changes in phenotype that result from biological and technological manipulation

Locomotor adaptability in persons with unilateral transtibial amputation

Background Locomotor adaptation enables walkers to modify strategies when faced with challenging walking conditions. While a variety of neurological injuries can impair locomotor adaptability, the effect of a lower extremity amputation on adaptability is poorly understood. Objective Determine if locomotor adaptability is impaired in persons with unilateral transtibial amputation (TTA). Methods The locomotor adaptability of 10 persons with a TTA and 8 persons without an amputation was tested while walking on a split-belt treadmill with the parallel belts running at the same (tied) or different (split) speeds. In the split condition, participants walked for 15 minutes with the respective belts moving at 0.5 m/s and 1.5 m/s. Temporal spatial symmetry measures were used to evaluate reactive accommodations to the perturbation, and the adaptive/de-adaptive response. Results Persons with TTA and the reference group of persons without amputation both demonstrated highly symmetric walking at baseline. During the split adaptation and tied post-adaptation walking both groups responded with the expected reactive accommodations. Likewise, adaptive and de-adaptive responses were observed. The magnitude and rate of change in the adaptive and de-adaptive responses were similar for persons with TTA and those without an amputation. Furthermore, adaptability was no different based on belt assignment for the prosthetic limb during split adaptation walking. Conclusions Reactive changes and locomotor adaptation in response to a challenging and novel walking condition were similar in persons with TTA to those without an amputation. Results suggest persons with TTA have the capacity to modify locomotor strategies to meet the demands of most walking conditions despite challenges imposed by an amputation and use of a prosthetic limb

Physical and neural entrainment to rhythm: human sensorimotor coordination across tasks and effector systems.

The human sensorimotor system can be readily entrained to environmental rhythms, through multiple sensory modalities. In this review, we provide an overview of theories of timekeeping that make this neuroentrainment possible. First, we present recent evidence that contests the assumptions made in classic timekeeper models. The role of state estimation, sensory feedback and movement parameters on the organization of sensorimotor timing are discussed in the context of recent experiments that examined simultaneous timing and force control. This discussion is extended to the study of coordinated multi-effector movements and how they may be entrained

Effects of sleep deprivation on postural control

Sleep is an essential biological requirement for the human organism to regulate its physiological, physical, cognitive, psychological and emotional resources, according to its necessities, allowing the functionality to carry out daily activities successfully. Evidence claims that sleep deprivation has a negative impact on physical performance, motor development and quality of life. One of the components that reflects motor performance is postural control. Sleep deprivation decreases considerably the capacity of stabilizing the neuromuscular system and adapting to environmental constraints, leading to a greater propensity to injuries and falls. This study aims to investigate the effects of a 24-hour sleep deprivation on postural control. Seventeen healthy participants (age 23.88±2.42 years, height 1.75±0.06 m, weight 71.80±7.97 kg, body mass index 23.30±1.80 kg/m2) visited the laboratory on two occasions: pre and post 24 hours of sleep deprivation. In both sessions, participants performed the postural control assessment, using the posturography technique. The protocol consisted on stabilizing the body, standing on both legs over a platform, for two minutes, while remaining quiet. The evaluation was performed twice, under two conditions: with eyes opened, and with eyes closed. Linear parameters of the center of pressure data were analyzed. Non-linear parameters of variability in the regularity of postural control were also determined through the sample entropy metric. Paired samples t-tests or a Wilcoxon Signed-rank tests were performed to test the effect of sleep deprivation on all dependent variables. Nearly all linear parameters showed an increase after sleep deprivation (excluding range in the anterior-posterior direction in eyes opened condition, which was maintained), while sample entropy decreased. Our findings show that 24 hours of sleep deprivation negatively affects postural control. This study confirmed the observations of previous studies using linear variables and provided a new contribution regarding the effects of a 24-hour sleep deprivation on the complexity of postural control and motor performance. The measure of entropy reflects the adaptability of motor control and acts as an indirect index of the functional capacity of the human neuromuscular system. Accordingly, in a state of sleep deprivation, psychomotor, cognitive and adaptability capacities are reduced, suggesting that there is a greater probability of compromising the neuromuscular system and, consequently, a greater exposure to injuries and falls.O sono é um requisito biológico essencial para manter o organismo humano a regular o equilíbrio a nível fisiológico, físico, cognitivo, psicológico e emocional, de forma adequada e de acordo com as suas necessidades, permitindo restabelecer a sua funcionalidade para realizar as atividades diárias e garantir o seu bem-estar. Existe evidência de que a privação do sono tem um impacto negativo no desenvolvimento motor e na qualidade de vida. Uma das componentes que reflete o desempenho motor é o controlo postural. As situações de privação de sono aumentam consideravelmente as dificuldades na capacidade de estabilização do sistema neuromuscular e em adaptá-lo a constrangimentos do ambiente, tendendo a aumentar o risco de lesões e quedas. Desta forma, este estudo tem como objetivo investigar o efeito de 24 horas de privação do sono no controlo postural. Dezassete sujeitos saudáveis (idade 23.88±2.42 anos, altura 1.75±0.06 m, massa corporal 71.80±7.97 kg, índice de massa corporal 23.30±1.80 kg/m2) visitaram o laboratório em duas ocasiões; pré e pós 24 horas de privação do sono. Nas duas sessões, os participantes realizaram a avaliação do controlo postural a partir da técnica de posturografia. O protocolo consistiu na estabilização da postura em pé e bipedal, durante dois minutos. A avaliação realizou-se duas vezes, sob duas condições: olhos abertos e olhos fechados. Foram analisados os parâmetros lineares que caracterizam o equilíbrio postural, a partir dos dados do centro de pressão. Foram também determinados parâmetros não lineares de variação da regularidade do controlo postural, através da métrica da entropia amostral, na direção ântero-posterior (SampEn AP) e médio-lateral (SampEn ML). Foram efetuados testes t para amostras emparelhadas e os testes de Wilcoxon para testar o efeito da privação do sono de todas as variáveis dependentes. Em quase todos os parâmetros lineares foi observado um aumento depois da privação de sono (com exceção da amplitude na direção ântero-posterior na condição de olhos abertos, que se manteve), enquanto a entropia amostral diminuiu. Os resultados indicam que a privação de 24 horas de sono afeta negativamente o controlo postural. Este estudo confirmou as observações de estudos anteriores a partir de variáveis lineares e ainda forneceu um novo contributo em relação aos efeitos da privação do sono na complexidade do controlo postural e do controlo motor. A medida reflete a adaptabilidade do controlo motor e atua como uma medida indireta da capacidade funcional do sistema neuromuscular humano. Um estado de 24 horas de privação de sono contribuiu para a redução das capacidades psicomotoras, cognitivas e a adaptabilidade aos constrangimentos, sugerindo-se que existe maior probabilidade em comprometer o sistema neuromuscular e, consequente, maior exposição para ocorrência de lesões e quedas

On Neuromechanical Approaches for the Study of Biological Grasp and Manipulation

Biological and robotic grasp and manipulation are undeniably similar at the level of mechanical task performance. However, their underlying fundamental biological vs. engineering mechanisms are, by definition, dramatically different and can even be antithetical. Even our approach to each is diametrically opposite: inductive science for the study of biological systems vs. engineering synthesis for the design and construction of robotic systems. The past 20 years have seen several conceptual advances in both fields and the quest to unify them. Chief among them is the reluctant recognition that their underlying fundamental mechanisms may actually share limited common ground, while exhibiting many fundamental differences. This recognition is particularly liberating because it allows us to resolve and move beyond multiple paradoxes and contradictions that arose from the initial reasonable assumption of a large common ground. Here, we begin by introducing the perspective of neuromechanics, which emphasizes that real-world behavior emerges from the intimate interactions among the physical structure of the system, the mechanical requirements of a task, the feasible neural control actions to produce it, and the ability of the neuromuscular system to adapt through interactions with the environment. This allows us to articulate a succinct overview of a few salient conceptual paradoxes and contradictions regarding under-determined vs. over-determined mechanics, under- vs. over-actuated control, prescribed vs. emergent function, learning vs. implementation vs. adaptation, prescriptive vs. descriptive synergies, and optimal vs. habitual performance. We conclude by presenting open questions and suggesting directions for future research. We hope this frank assessment of the state-of-the-art will encourage and guide these communities to continue to interact and make progress in these important areas

The Effects of Neuromuscular Fatigue on the Complexity of Isometric Torque Output in Humans

The temporal structure, or complexity, of torque output is thought to reflect the adaptability of motor control and has important implications for system function, with high values endowing greater adaptability in response to alterations in task demand. The aim of this thesis was to investigate the effect of neuromuscular fatigue on the complexity of isometric muscle torque output. It was hypothesised that neuromuscular fatigue would lead to a reduction in the complexity of muscle torque output, as measured by approximate entropy (ApEn), sample entropy (SampEn) and the detrended fluctuation analysis (DFA) ? scaling exponent. The first experimental study (Chapter 4) demonstrated that muscle torque complexity was significantly reduced during both maximal and submaximal intermittent fatiguing contractions, with the values at task failure indicative of increasingly Brownian noise (DFA ? > 1.50). It was subsequently shown in the second study (Chapter 5) that this reduction in complexity occurred exclusively during contractions performed above the critical torque. It was next demonstrated, in the third study (Chapter 6), that pre-existing fatigue significantly reduced torque complexity and time to task failure, but still resulted in consistent values of complexity at task failure regardless of the time taken to reach that point. In the fourth study (Chapter 7) caffeine ingestion was found to slow the rate of reduction in torque complexity with fatigue, seemingly through both central and peripheral mechanisms. Finally, in the fifth study (Chapter 8) eccentric exercise decreased the complexity of torque output, with values only recovering to baseline levels after 24 hours recovery, in comparison to only 10 minutes recovery following isometric exercise. These results demonstrate that torque complexity is significantly perturbed by neuromuscular fatigue. This thesis has thus provided substantial evidence that the complexity of motor control during force production becomes less complex, and that muscles become less adaptable, with neuromuscular fatigue

Changes in torque complexity with fatigue : unravelling the role of neuromuscular coordination mechanisms

Physiological complexity is believed to reflect a system’s adaptability to environmental challenges. Torque complexity reflects the adaptability of motor control and has been proposed as an indirect indicator of the functional capacity of the neuromuscular system. While torque complexity has been shown to decrease with aging, disease and fatigue, its underlying mechanisms are not yet fully understood. Thus, the present study aimed to investigate the neurophysiological mechanisms underlying torque complexity. Twenty-one healthy and young adults (age: 24.62 ± 3.51yrs; height: 1.77 ± 0.07m; weight: 74.57 ± 13.34kg; BMI: 23.68 ± 3.30kg/m2) took part in the present study and visited the laboratory on one occasion. Participants performed three extension and flexion Maximal Voluntary Isometric Contractions (MVIC) proceeded by two repetitions of a thirty-second long submaximal isometric contraction at 30% MVIC. Participants then performed the fatiguing protocol, which consisted of a series of concentric and eccentric knee extensions until exhaustion at 90º/s. Immediately after, participants performed the same tests as prior to the fatiguing protocol. Peak Torque (PT) and Rate of Torque Development (RTD) were determined from the MVIC trials. Torque signals were sampled continuously, and the metrics of variability and complexity were calculated based on submaximal contractions trials. The coefficient of variation (CV) was used to quantify torque variability, while torque complexity was determined through Sample Entropy (SampEn). Electromyographic (EMG) signals, specifically, motor unit-related parameters, EMG amplitude, EMG CV and EMG co-contraction index (CCi) were also extracted from the submaximal trials. Paired sampled t-tests or Wilcoxon Signed-rank tests were used to test the effect of fatigue in all the dependent variables. Additionally, a stepwise multiple linear regression analysis was conducted to examine the contribution of other parameters to explain changes in torque complexity. Torque SampEn and CV were not altered with fatigue. PT and RTD significantly decreased whereas EMG amplitude, CCi, motor unit action potential amplitude (MUAPa) and average firing rate (FRa) significantly increased with fatigue. The multiple linear regression analysis revealed that FR/MUAPslope, FR/MUAPintercept and torque’s CV significantly explained changes in torque complexity accounting for 80.5% of its variance. Interestingly, changes in torque complexity were mainly attributed to intramuscular coordination processes which should be taken into consideration when planning training process and competition cycles.A complexidade fisiológica é considerada uma medida que reflete a capacidade de adaptação de um sistema biológico a alterações no contexto em que ele está inserido. A complexidade do torque caracteriza-se como a adaptabilidade do controlo motor sendo vista como um indicador indireto da capacidade funcional do sistema neuromuscular. Os fenómenos de envelhecimento, doença e fadiga constituem-se como fatores responsáveis pela diminuição da complexidade do torque; no entanto, os mecanismos responsáveis por esta alteração ainda não são compreendidos na sua totalidade. Assim, o presento estudo tem como objetivo investigar os mecanismos responsáveis pela alteração da complexidade do torque com a fadiga. Vinte e um adultos jovens e saudáveis (idade: 24.62 ± 3.51anos; altura: 1.77 ± 0.07m; massa corporal: 74.57 ± 13.34kg; IMC: 23.68 ± 3.30kg/m2) participaram no presente estudo e visitaram o laboratório numa única ocasião. Os participantes realizaram três Contrações Isométricas Voluntárias Máximas (MVIC) de extensão e flexão, procedidas por duas contrações isométricas submáximas com a duração de trinta segundas a 30% MVIC. De seguida, os participantes realizaram o protocolo de fadiga que consistiu numa série de extensões do joelho concêntricas e excêntricas até à exaustão a 90º/s. Imediatamente após, os participantes repetiram os testes realizados antes do protocolo de fadiga. O Peak Torque (PT) e a Taxa de Produção de Torque (RTD) foram determinados a partir das tarefas MVIC. Os dados do torque foram recolhidos de forma contínua e as métricas da variabilidade e da complexidade foram calculadas a partir das contrações submáximas. O coeficiente de variação (CV) foi usado para quantificar a magnitude da variabilidade do torque e a complexidade do torque foi determinada através da Sample Entropy (SampEn). As medidas da eletromiografia (EMG), nomeadamente, os parâmetros relacionados com as unidades motoras, a amplitude do EMG, o CV do EMG e o índex de co-contração do EMG (CCi) também foram extraídos a partir das tarefas submáximas. Os testes t para amostras emparelhadas e os testes de Wilcoxon foram usados para testar o efeito da fadiga em todas as variáveis dependentes. Adicionalmente, foi realizada uma análise de regressão linear múltipla para examinar a contribuição de outros parâmetros para a explicação de alterações na complexidade do torque. Não houve diferenças na SampEn e no CV do torque com a fadiga. Com a fadiga, o PT e a RTD diminuíram significativamente. Por outro lado, a amplitude do EMG, o CCi, a amplitude dos potenciais de ação das unidades motoras (MUAPa) e a frequência de descarga média (FRa) aumentaram significativamente com a instalação da fadiga. A análise de regressão linear múltipla demonstrou que o FR/MUAPslope, o FR/MUAPintercept e o CV do torque explicam significativamente 80.5% das alterações na complexidade do torque. Deste modo, as alterações na complexidade do torque foram maioritariamente explicadas por mecanismos de coordenação intramuscular, os quais devem ser tidos em consideração no processo de planeamento do treino e dos ciclos competitivos

Visual cue training to improve walking and turning after stroke:a study protocol for a multi-centre, single blind randomised pilot trial

Visual information comprises one of the most salient sources of information used to control walking and the dependence on vision to maintain dynamic stability increases following a stroke. We hypothesize, therefore, that rehabilitation efforts incorporating visual cues may be effective in triggering recovery and adaptability of gait following stroke. This feasibility trial aims to estimate probable recruitment rate, effect size, treatment adherence and response to gait training with visual cues in contrast to conventional overground walking practice following stroke.Methods/design: A 3-arm, parallel group, multi-centre, single blind, randomised control feasibility trial will compare overground visual cue training (O-VCT), treadmill visual cue training (T-VCT), and usual care (UC). Participants (n = 60) will be randomly assigned to one of three treatments by a central randomisation centre using computer generated tables to allocate treatment groups. The research assessor will remain blind to allocation. Treatment, delivered by physiotherapists, will be twice weekly for 8 weeks at participating outpatient hospital sites for the O-VCT or UC and in a University setting for T-VCT participants.Individuals with gait impairment due to stroke, with restricted community ambulation (gait spee

Effect of Aging on the Lower Limb Kinematics in Karate Practitioners: Comparing Athletes and Their Senseis

With the life expectancy increasing, older adult population has gained the attention of many researchers. Aging is known to lead to a general decline in bodily functions, which affect the quality of life. The aim of this study was to analyze how the aging process affects veteran active karate practitioners, in the kinematic and temporal structure of the frontal kick. Nine black belt karate practitioners over 50 years old and 24 black belt karate practitioners, aged between 20 and 30 years old, all male, performed the frontal kick mae-geri. Results showed that knee is the structure that holds most differences between young and veterans, both for linear and for angular variables during the mae-geri performance. Statistical differences were found in linear velocity for the knee; linear acceleration of the knee, hip, and RASIS; maximum angular velocity for knee and hip; maximum angular acceleration for ankle and hip; and in the range of motion of knee. The temporal variables show differences, between groups, in maximum linear velocity, maximum linear acceleration, and maximum angular acceleration. However, no differences were found between groups for the time before contact in the maximum linear and angular acceleration, which allow us to remark both the effects of the aging process and the effect of training. This study corroborates the ability of older people to achieve benefits from sports practice, achieving higher efficiency than the younger adults in task execution, but using different motor control strategies.info:eu-repo/semantics/publishedVersio

Research issues in implementing remote presence in teleoperator control

The concept of remote presence in telemanipulation is presented. A conceptual design of a prototype teleoperator system incorporating remote presence is described. The design is presented in functional terms, sensor, display, and control subsystem. An intermediate environment, in which the human operator is made to feel present, is explicated. The intermediate environment differs from the task environment due to the quantity and type of information presented to an operator and due to scaling factors protecting the operator from the hazards of the task environment. Potential benefits of remote presence systems, both for manipulation and for the study of human cognition and preception are discussed