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The time course of the center of pressure (CoP) during human quiet standing, corresponding to body sway, is a stochastic process, influenced by a variety of features of the underlying neuro‐musculo‐skeletal system, such as postural stability and flexibility. Due to complexity of the process, sway patterns have been characterized in an empirical way by a number of indices, such as sway size and mean sway velocity. Here, we describe a statistical approach with the aim of estimating “universal” indices, namely parameters that are independent of individual body characteristics and thus are not “hidden” by the presence of individual, daily, and circadian variations of sway; in this manner it is possible to characterize the common aspects of sway dynamics across healthy young adults, in the assumption that they might reflect underlying neural control during quiet standing. Such universal indices are identified by analyzing intra and inter‐subject variability of various indices, after sorting out individual‐specific indices that contribute to individual discriminations. It is shown that the universal indices characterize mainly slow components of sway, such as scaling exponents of power‐law behavior at a low‐frequency regime. On the other hand, most of the individual‐specific indices contributing to the individual discriminations exhibit significant correlation with body parameters, and they can be associated with fast oscillatory components of sway. These results are consistent with a mechanistic hypothesis claiming that the slow and the fast components of sway are associated, respectively, with neural control and biomechanics, supporting our assumption that the universal characteristics of postural sway might represent neural control strategies during quiet standing. The time course of the center of pressure (CoP) during human quiet standing, corresponding to body sway, is a stochastic process, influenced by a variety of features of the underlying neuro‐musculo‐skeletal system, such as postural stability and flexibility. Here, we describe a statistical approach with the aim of estimating “universal” indices, namely parameters that are independent of individual body characteristics and thus are not “hidden” by the presence of individual, daily, and circadian variations of sway, to characterize the common aspects of sway dynamics across healthy young adults in the assumption that they might reflect underlying neural control during quiet stance. It is shown that the universal indices characterize mainly slow components of sway, such as scaling exponents of power‐law behavior at a low‐frequency regime.

Background: It has recently been noticed that the quantity of stress affects postural stability in young women. The study was conducted with the goal of investigating whether increased stress may damagingly effect posture control in 90 young men (71 right-handed and 19 left-handed) while maintaining an upright bipedal posture, while keeping their eyes open or closed. Perceived Stress Scale (PSS) was administered and changes in free cortisol levels were monitored (Cortisol Awakening Response, CAR) in order to evaluate the amount of stress present during awakening, while the Profile of Mood States (POMS) was used to estimate distress on the whole. Posture control was evaluated with the use of a force platform, which, while computing a confidence ellipse area of 95%, was engaged by the Center of Pressure through five stability stations and was sustained for a minimum of 52 s, with and without visual input. Another goal of the experiment was to find out whether or not cortisol increases in CAR were linked with rises of blood lactate levels. Results: CAR, PSS and POMS were found to be extensively related. Furthermore, it has been observed that increases in salivary cortisol in CAR are associated with small but significant increases in blood lactate levels. As expected, stress levels did affect postural stability. Conclusions: The results of the present study confirm that the level of stress can influence postural stability, and that this influence is principally obvious when visual information is not used in postural control.

Depth information is important for postural stability and is generated by two visual systems: binocular and motion parallax. The effect of each type of parallax on postural stability remains unclear. We investigated the effects of binocular and motion parallax loss on static postural stability using a virtual reality (VR) system with a head-mounted display (HMD). A total of 24 healthy young adults were asked to stand still on a foam surface fixed on a force plate. They wore an HMD and faced a visual background in the VR system under four visual test conditions: normal vision (Control), absence of motion parallax (Non-MP)/binocular parallax (Non-BP), and absence of both motion and binocular parallax (Non-P). The sway area and velocity in the anteroposterior and mediolateral directions of the center-of-pressure displacements were measured. All postural stability measurements were significantly higher under the Non-MP and Non-P conditions than those under the Control and Non-BP conditions, with no significant differences in the postural stability measurements between the Control and Non-BP conditions. In conclusion, motion parallax has a more prominent effect on static postural stability than binocular parallax, which clarifies the underlying mechanisms of postural instability and informs the development of rehabilitation methods for people with visual impairments.

A novel and fun exercise robot (LOCOBOT) was developed to improve balance ability. This system can control a spherical robot on a floor by changing the center of pressure (COP) based on weight-shifting on a board. The present study evaluated leg muscle activity and joint motion during LOCOBOT exercise and compared the muscle activity with walking and sit-to-stand movement. This study included 10 healthy male adults (age: 23.0 ± 0.9 years) and examined basic LOCOBOT exercises (front–back, left–right, 8-turn, and bowling). Electromyography during each exercise recorded 13 right leg muscle activities. Muscle activity was represented as the percentage maximal voluntary isometric contraction (%MVIC). Additionally, the joint motion was simultaneously measured using an optical motion capture system. The mean %MVIC differed among LOCOBOT exercises, especially in ankle joint muscles. The ankle joint was primarily used for robot control. The mean %MVIC of the 8-turn exercise was equivalent to that of walking in the tibialis anterior, and the ankle plantar flexors were significantly higher than those in the sit-to-stand motion. Participants control the robot by ankle strategy. This robot exercise can efficiently train the ankle joint muscles, which would improve ankle joint stability.

An association is observed between the standing sway posture and falls in patients with stroke; hence, it is important to study their standing balance. Although there are studies on the standing balance in stroke patients, differences in control have not been adequately investigated. This study aims to propose a method to characterize the postural sway in standing stroke patients using a mathematical model. A musculoskeletal model and neural controller model were used to simulate ten stroke patients (five patients with cerebral hemorrhages and five patients with cerebral infarctions) and eight young healthy participants, and their data were monitored during quiet standing. The model parameters were adjusted by focusing on the maximum-minimum difference in sway, which was considered important in a previous study, and sway speed, which is frequently used in the analysis. The adjusted model parameters were subjected to dimension reduction using non-negative matrix factorization. Consequently, the sway characteristics of stroke patients were expressed as the magnitude of gain parameters related to the extension of the entire body. The results of this study demonstrated the possibility of representing the characteristics of postural sway as model parameters in stroke patients using a mathematical model. This characterization could lead to the design of individualized rehabilitation systems in the future.

Introduction: Shifting from static to dynamic balance can influence cognitive performance, particularly in tasks like mental rotation. Objective: This study investigates the impact of different postural balance conditions on visual spatial cognitive abilities, specifically mental rotation tasks involving rotated 3D cubes and human body images, in gymnasts, handball players, and video gamers under the age of twelve. Methodology: Fifty volunteers under the age of twelve (i.e., 12 gymnasts, 18 handball players, and 20 video gamers) participated in this study. The experiment involved mental rotation tasks (i.e., object-based 3D cube and human body conditions) under four different balance conditions: without balance, static balance, dynamic frontal balance, and dynamic sagittal balance, on a stabilometric platform. Cognitive performance was assessed by measuring response time and error rate, and postural control was evaluated using center of pressure (COP) sway, acceleration, and displacement. Results: The results revealed significant immediate beneficial effects of dynamic balance on cognitive tasks. Specifically, dual tasks enhanced performance in postural control and mental rotation tasks, with reduced response time and center of pressure sway (p<0.01). Discussion: Athletes demonstrated greater improvements compared to non-athletes, highlighting the positive effect of regular physical training involving postural control to enhance cognitive abilities. Conclusions: These results suggest that participation in sports during childhood enhances sensorimotor systems, neuromuscular control and balance, which are critical for maintaining stability and developing cognitive abilities. Integrating balance training and cognitive challenges into physical training may therefore optimize both cognitive and motor performance in young athletes. Introducción: La transición del equilibrio estático al dinámico puede influir en el rendimiento cognitivo, particularmente en tareas como la rotación mental.  Objetivo: Este estudio investiga el impacto de diferentes condiciones de equilibrio postural en las habilidades cognitivas visoespaciales, específicamente tareas de rotación mental que involucran cubos 3D rotados e imágenes del cuerpo humano, en gimnastas, balonmanistas y video jugadores menores de doce años.  Metodología: Cincuenta jóvenes voluntarios menores de doce años (12 gimnastas, 18 balonmanistas y 20 video jugadores) participaron en este estudio. El experimento incluyó tareas de rotación mental (cubos 3D y cuerpos humanos) bajo cuatro condiciones: sin equilibrio, equilibrio estático, equilibrio dinámico frontal y equilibrio dinámico sagital en una plataforma estabilométrica. l rendimiento cognitivo se evaluó mediante tiempo de respuesta y tasa de error, mientras el control postural se midió mediante oscilación, aceleración y desplazamiento del centro de presión (COP). Resultados: Se observaron efectos beneficiosos inmediatos significativos del equilibrio dinámico en las tareas cognitivas. Las tareas duales mejoraron el rendimiento en control postural y rotación mental, con reducción del tiempo de respuesta y oscilación del COP (p<0,01). Discusión: Los atletas mostraron mayores mejoras que los no atletas, destacando el efecto positivo del entrenamiento físico regular con control postural para potenciar habilidades cognitivas.  Conclusiones: Estos resultados sugieren que la práctica deportiva en la infancia mejora los sistemas sensorimotores, el control neuromuscular y el equilibrio, críticos para mantener la estabilidad y desarrollar habilidades cognitivas. Integrar entrenamiento de equilibrio y desafíos cognitivos en el entrenamiento físico podría optimizar tanto el rendimiento cognitivo como motor en jóvenes atletas. Introdução: A transição do equilíbrio estático para o dinâmico pode influenciar o desempenho cognitivo, particularmente em tarefas como a rotação mental. Objectivo: Este estudo investiga o impacto de diferentes condições de equilíbrio postural nas capacidades cognitivas viso-espaciais, especificamente tarefas de rotação mental envolvendo cubos 3D rotacionados e imagens do corpo humano, em ginastas, jogadores de andebol e jogadores de videojogos com menos de 12 anos. Metodologia: Participaram neste estudo cinquenta jovens voluntários com menos de 12 anos (12 ginastas, 18 jogadores de andebol e 20 jogadores de videojogos). A experiência incluiu tarefas de rotação mental (cubos 3D e corpos humanos) em quatro condições: sem equilíbrio, equilíbrio estático, equilíbrio dinâmico frontal e equilíbrio dinâmico sagital numa plataforma estabilométrica. O desempenho cognitivo foi avaliado pelo tempo de resposta e pela taxa de erro, enquanto o controlo postural foi medido pela oscilação, aceleração e deslocamento do centro de pressão (COP). Resultados: Foram observados efeitos benéficos imediatos significativos do equilíbrio dinâmico em tarefas cognitivas. As tarefas duplas melhoraram o desempenho no controlo postural e na rotação mental, com redução do tempo de resposta e da oscilação do COP (p < 0,01). Discussão: Os atletas apresentaram maiores melhorias do que os não atletas, realçando o efeito positivo do treino físico regular com controlo postural na melhoria das capacidades cognitivas. Conclusões: Estes resultados sugerem que a prática desportiva na infância melhora os sistemas sensório-motor, o controlo neuromuscular e o equilíbrio, que são essenciais para a manutenção da estabilidade e o desenvolvimento das capacidades cognitivas. A integração do treino de equilíbrio e dos desafios cognitivos no treino físico pode otimizar o desempenho cognitivo e motor em atletas jovens.

Muscular fatigue can affect postural control processes by impacting on the neuromuscular and somatosensory system. It is assumed that this leads to an increased risk of injury, especially in sports such as alpine skiing that expose the body to strong and rapidly changing external forces. In this context, posture constraints and contraction-related muscular pressure may lead to muscular deoxygenation. This study investigates whether these constraints and pressure affect static and dynamic postural control. To simulate impaired blood flow in sports within a laboratory task, oxygen saturation was manipulated locally by using an inflatable cuff to induce blood flow restriction (BFR). Twenty-three subjects were asked to stand on a perturbatable platform used to assess postural-related movements. Using a 2 × 2 within-subject design, each participant performed postural control tasks both with and without BFR. BFR resulted in lower oxygenation of the m. quadriceps femoris ( p = 0.024) and was associated with a significantly lower time to exhaustion (TTE) compared to the non-restricted condition [ F (1,19) = 16.22, p < 0.001, η p 2 = 0.46]. Perturbation resulted in a significantly increased TTE [ F (1,19) = 7.28, p = 0.014, η p 2 = 0.277]. There were no significant effects on static and dynamic postural control within the saturation conditions. The present data indicate that BFR conditions leads to deoxygenation and a reduced TTE. Postural control and the ability to regain stability after perturbation were not affected within this investigation.

Human postural sway during stance arises from coordinated multi-joint movements. Thus, a sway trajectory represented by a time-varying postural vector in the multiple-joint-angle-space tends to be constrained to a low-dimensional subspace. It has been proposed that the subspace corresponds to a manifold defined by a kinematic constraint, such that the position of the center of mass (CoM) of the whole body is constant in time, referred to as the kinematic uncontrolled manifold ( ). A control strategy related to this hypothesis ( ) claims that the central nervous system (CNS) aims to keep the posture close to the kinematic-UCM using a continuous feedback controller, leading to sway patterns that mostly occur within the kinematic-UCM, where no corrective control is exerted. An alternative strategy proposed by the authors ( ) claims that the CNS stabilizes posture by intermittently suspending the active feedback controller, in such a way to allow the CNS to exploit a stable manifold of the saddle-type upright equilibrium in the state-space of the system, referred to as the , when the state point is on or near the manifold. Although the mathematical definitions of the kinematic- and dynamic-UCM are completely different, both UCMs play similar roles in the stabilization of multi-joint upright posture. The purpose of this study was to compare the dynamic performance of the two control strategies. In particular, we considered a double-inverted-pendulum-model of postural control, and analyzed the two UCMs defined above. We first showed that the geometric configurations of the two UCMs are almost identical. We then investigated whether the UCM-component of experimental sway could be considered as passive dynamics with no active control, and showed that such UCM-component mainly consists of high frequency oscillations above 1 Hz, corresponding to anti-phase coordination between the ankle and hip. We also showed that this result can be better characterized by an eigenfrequency associated with the dynamic-UCM. In summary, our analysis highlights the close relationship between the two control strategies, namely their ability to simultaneously establish small CoM variations and postural stability, but also make it clear that the intermittent control hypothesis better explains the spectral characteristics of sway.

Numerous of our daily activities are performed within multitask or dual task conditions. These conditions involve the interaction of perceptual and motor processes involved in postural control. Age-related changes may negatively impact cognition and balance control. Studies identifying changes related to dual-task actions in older people are need. This study aimed to determine the effects of different types of dual-tasking on the balance control of healthy older adults. The sample included 36 community-living older adults, performing two tests—a sway test and a timed up-and-go test—in three conditions: (a) single motor task; (b) dual motor task; and (c) dual motor task with cognitive demands. Cognitive processes (dual-task and cognition) affected static balance, increasing amplitude (p < 0.001) and frequency (p < 0.001) of the center of mass displacements. Dynamic balance revealed significant differences between the single motor condition and the other two conditions during gait phases (p < 0.001). The effect of dual-tasking in older adults suggests that cognitive processes are a main cause of increased variability in balance and gait when under an automatic control. During sit-to-stand, turning, and turn-to-sit movements under dual-tasking, the perceptive information becomes the most important focus of attention, while any cognitive task becomes secondary.