Diabetic older women without peripheral neuropathy amplify body sway but are capable of improving postural stability during a saccadic gaze task.

BACKGROUND: Diabetic older people tend to present deteriorated performance in balance and locomotion activities, even those without peripheral neuropathy. There is evidence that saccadic eye movements are used to reduce body sway in young and older healthy adults, but it has not been shown that diabetic older people preserve this visuomotor adaptation capacity. RESEARCH QUESTION: Are diabetic older women without peripheral neuropathy capable of improving postural stability during a saccadic gaze task? METHODS: Seventeen type 2 diabetic older women (68.2 ± 10.7 years old) and seventeen healthy women, age-matched controls (66.0 ± 8.4 years old) voluntarily participated in the study. All participants were instructed to stand upright, barefoot, as stable as possible, for 30 s. Participants maintained their feet parallel to each other, at standard and narrow bases of support, while either fixating on a stationary target (fixation condition) or performing horizontal saccadic eye movements to follow a target (eccentricity of 11° of visual angle), which continuously disappeared and reappeared immediately on the opposite side (saccade 0.5 Hz and saccade 1.1 Hz conditions). RESULTS: Results indicated that the diabetic group clearly had deteriorated postural control, as shown by increased values of mean sway amplitude and mean sway velocity. However, diabetic and control groups were similarly capable of using saccadic eye movements to improve their postural stability, reducing their sway velocity compared to a gaze fixation condition. SIGNIFICANCE: Diabetes per se (without peripheral neuropathy) amplifies postural sway of older women as compared to their healthy age-matched controls. However, diabetic older women without peripheral neuropathy are capable of improving postural stability during a saccadic gaze task.

Combined Aerobic and Strength Training Improves Dynamic Stability and can Prevent against Static Stability Decline in Postmenopausal Women: A Randomized Clinical Trial.

OBJECTIVE: To analyze the effect of combined training (CT) in postural control and gait parameters in postmenopausal women. METHODS: A parallel-group, randomized, control study was conducted with 16 weeks of combined training (n = 16) versus a non-training control group (n = 12) in postmenopausal women (aged 59.3 ± 8.0). Pre and postintervention assessments included postural control (using an AMTI force platform - Advanced Mechanical Technology, Inc., Watertown, MA, USA) and gait impairments (using baropodometry). In addition, the upper limb strength and abdominal tests, as well as aerobic capacity, assessed functional indicators. RESULTS: The CT intervention in postmenopausal women resulted in improved gait (stride length (p = 0.006); speed (p = 0.013); double support time (p = 0.045); and improved postural control (displacement area of postural sway in a normal base of support with eyes open (p = 0.006). Combined training increased functional indicators (abdominal - p = 0.031; aerobic capacity - p = 0.002). CONCLUSION: In conclusion, combined aerobic plus strength training effectively improved gait and balance control in older women. The postmenopausal women from the CT group walked faster and with bigger steps after the intervention than the control group. In addition, they presented decreased postural sway in standing and decreased the percentage of double support time while walking, which means improved static and dynamic balance control and functional indicators.

OBJETIVO: Analisar o efeito do treinamento combinado (TC) no controle postural e nos parâmetros da marcha em mulheres na pós-menopausa. MéTODOS: Foi realizado um estudo controlado randomizado de grupos paralelos com 16 semanas de treinamento combinado (n = 16) versus um grupo controle sem treinamento (n = 12) em mulheres na pós-menopausa (59,3 ± 8,0 anos). As avaliações pré e pós-intervenção incluíram controle postural (usando a plataforma de força AMTI) e deficiências da marcha (usando baropodometria). Além disso, os testes de força de membros superiors e abdominal, bem como a capacidade aeróbica, avaliaram indicadores funcionais. RESULTADOS: A intervenção do TC em mulheres na pós-menopausa resultou em melhora da marcha (comprimento da passada (p = 0,006), velocidade (p = 0,013), tempo de apoio duplo (p = 0,045) e controle postural aprimorado (área de deslocamento da oscilação postural em base de apoio normal com olhos abertos (p = 0,006). O TC aumentou os indicadores funcionais (abdominal - p = 0,031; capacidade aeróbia - p = 0,002). CONCLUSãO: Em conclusão, o TC de força e aeróbico melhorou efetivamente o controle da marcha e do equilíbrio em mulheres idosas. As mulheres na pós-menopausa do grupo CT caminharam mais rápido e com passos maiores após a intervenção do que o grupo controle. Além disso, elas apresentaram redução da oscilação postural em pé e do percentual de tempo de apoio duplo durante a caminhada, o que significa melhora no controle do equilíbrio estático e dinâmico e dos indicadores funcionais.

Does joint impedance improve dynamic leg simulations with explicit and implicit solvers?

The nervous system predicts and executes complex motion of body segments actuated by the coordinated action of muscles. When a stroke or other traumatic injury disrupts neural processing, the impeded behavior has not only kinematic but also kinetic attributes that require interpretation. Biomechanical models could allow medical specialists to observe these dynamic variables and instantaneously diagnose mobility issues that may otherwise remain unnoticed. However, the real-time and subject-specific dynamic computations necessitate the optimization these simulations. In this study, we explored the effects of intrinsic viscoelasticity, choice of numerical integration method, and decrease in sampling frequency on the accuracy and stability of the simulation. The bipedal model with 17 rotational degrees of freedom (DOF)-describing hip, knee, ankle, and standing foot contact-was instrumented with viscoelastic elements with a resting length in the middle of the DOF range of motion. The accumulation of numerical errors was evaluated in dynamic simulations using swing-phase experimental kinematics. The relationship between viscoelasticity, sampling rates, and the integrator type was evaluated. The optimal selection of these three factors resulted in an accurate reconstruction of joint kinematics (err < 1%) and kinetics (err < 5%) with increased simulation time steps. Notably, joint viscoelasticity reduced the integration errors of explicit methods and had minimal to no additional benefit for implicit methods. Gained insights have the potential to improve diagnostic tools and accurize real-time feedback simulations used in the functional recovery of neuromuscular diseases and intuitive control of modern prosthetic solutions.

Overweight Impairs Postural Control of Female Night Workers.

Objectives To verify the relationships between sleep duration (Total Sleep Time - TST) and postural control of female night workers before and after shift. As well as, to verify if there is an influence of the body mass index (BMI) on the postural control of these female workers before and after shift. Methods A total of 14 female night workers (mean age: 35.0 ± 7.7 years) were evaluated. An actigraph was placed on the wrist to evaluate the sleep-wake cycle. The body mass and height were measured, and BMI was calculated. Postural control was evaluated by means of a force platform, with eyes opened and eyes closed before and after the 12-hour workday. Results There was an effect of the BMI on the velocity and the center of pressure path with eyes opened before ( t = 2.55, p = 0.02) and after ( t = 4.10, p < 0.01) night work. The BMI impaired the velocity and the center of pressure path with eyes closed before ( t = 3.05, p = 0.01; t = 3.04, p = 0.01) and after ( t = 2.95, p = 0.01; t = 2.94, p = 0.01) night work. Furthermore, high BMI is associated with female workers' postural sway ( p < 0.05). Conclusion Therefore, high BMI impairs the postural control of female night workers, indicating postural instability before and after night work.

Does joint impedance improve dynamic leg simulations with explicit and implicit solvers?

The nervous system predicts and executes complex motion of body segments actuated by the coordinated action of muscles. When a stroke or other traumatic injury disrupts neural processing, the impeded behavior has not only kinematic but also kinetic attributes that require interpretation. Biomechanical models could allow medical specialists to observe these dynamic variables and instantaneously diagnose mobility issues that may otherwise remain unnoticed. However, the real-time and subject-specific dynamic computations necessitate the optimization these simulations. In this study, we explored the effects of intrinsic viscoelasticity, choice of numerical integration method, and decrease in sampling frequency on the accuracy and stability of the simulation. The bipedal model with 17 rotational degrees of freedom (DOF)-describing hip, knee, ankle, and standing foot contact-was instrumented with viscoelastic elements with a resting length in the middle of the DOF range of motion. The accumulation of numerical errors was evaluated in dynamic simulations using swing-phase experimental kinematics. The relationship between viscoelasticity, sampling rates, and the integrator type was evaluated. The optimal selection of these three factors resulted in an accurate reconstruction of joint kinematics (err < 1%) and kinetics (err < 5%) with increased simulation time steps. Notably, joint viscoelasticity reduced the integration errors of explicit methods and had minimal to no additional benefit for implicit methods . Gained insights have the potential to improve diagnostic tools and accurize real-time feedback simulations used in the functional recovery of neuromuscular diseases and intuitive control of modern prosthetic solutions.

Benefits associated with the standing position during visual search tasks.

The literature on postural control highlights that task performance should be worse in challenging dual tasks than in a single task, because the brain has limited attentional resources. Instead, in the context of visual tasks, we assumed that (i) performance in a visual search task should be better when standing than when sitting and (ii) when standing, postural control should be better when searching than performing the control task. 32 and 16 young adults participated in studies 1 and 2, respectively. They performed three visual tasks (searching to locate targets, free-viewing and fixating a stationary cross) displayed in small images (visual angle: 22°) either when standing or when sitting. Task performance, eye, head, upper back, lower back and center of pressure displacements were recorded. In both studies, task performance in searching was as good (and clearly not worse) when standing as when sitting. Sway magnitude was smaller during the search task (vs. other tasks) when standing but not when sitting. Hence, only when standing, postural control was adapted to perform the challenging search task. When exploring images, and especially so in the search task, participants rotated their head instead of their eyes as if they used an eye-centered strategy. Remarkably in Study 2, head rotation was greater when sitting than when standing. Overall, we consider that variability in postural control was not detrimental but instead useful to facilitate visual task performance. When sitting, this variability may be lacking, thus requiring compensatory movements.

Combined Aerobic and Strength Training Improves Dynamic Stability and can Prevent against Static Stability Decline in Postmenopausal Women: A Randomized Clinical Trial / O treinamento de força e aeróbio combinado melhora a estabilidade dinâmica e pode prevenir contra o declínio da estabilidade estática em mulheres na pósmenopausa: um ensaio clínico randomizado

Abstract Objective To analyze the effect of combined training (CT) in postural control and gait parameters in postmenopausal women. Methods A parallel-group, randomized, control study was conducted with 16 weeks of combined training (n = 16) versus a non-training control group (n = 12) in postmenopausal women (aged 59.3 ± 8.0). Pre and postintervention assessments included postural control (using an AMTI force platform - Advanced Mechanical Technology, Inc., Watertown, MA, USA) and gait impairments (using baropodometry). In addition, the upper limb strength and abdominal tests, as well as aerobic capacity, assessed functional indicators. Results The CT intervention in postmenopausal women resulted in improved gait (stride length (p = 0.006); speed (p = 0.013); double support time (p = 0.045); and improved postural control (displacement area of postural sway in a normal base of support with eyes open (p = 0.006). Combined training increased functional indicators (abdominal - p = 0.031; aerobic capacity - p = 0.002). Conclusion In conclusion, combined aerobic plus strength training effectively improved gait and balance control in older women. The postmenopausal women from the CT group walked faster and with bigger steps after the intervention than the control group. In addition, they presented decreased postural sway in standing and decreased the percentage of double support time while walking, which means improved static and dynamic balance control and functional indicators.

Resumo Objetivo Analisar o efeito do treinamento combinado (TC) no controle postural e nos parâmetros da marcha em mulheres na pós-menopausa. Métodos Foi realizado um estudo controlado randomizado de grupos paralelos com 16 semanas de treinamento combinado (n = 16) versus um grupo controle sem treinamento (n = 12) em mulheres na pós-menopausa (59,3 ± 8,0 anos). As avaliações pré e pós-intervenção incluíram controle postural (usando a plataforma de força AMTI) e deficiências da marcha (usando baropodometria). Além disso, os testes de força de membros superiors e abdominal, bem como a capacidade aeróbica, avaliaram indicadores funcionais. Resultados A intervenção do TC em mulheres na pós-menopausa resultou em melhora da marcha (comprimento da passada (p = 0,006), velocidade (p = 0,013), tempo de apoio duplo (p = 0,045) e controle postural aprimorado (área de deslocamento da oscilação postural em base de apoio normal com olhos abertos (p = 0,006). O TC aumentou os indicadores funcionais (abdominal - p = 0,031; capacidade aeróbia - p = 0,002). Conclusão Em conclusão, o TC de força e aeróbico melhorou efetivamente o controle da marcha e do equilíbrio em mulheres idosas. As mulheres na pós-menopausa do grupo CT caminharam mais rápido e com passos maiores após a intervenção do que o grupo controle. Além disso, elas apresentaram redução da oscilação postural em pé e do percentual de tempo de apoio duplo durante a caminhada, o que significa melhora no controle do equilíbrio estático e dinâmico e dos indicadores funcionais.

Daily physical activity in children enrolled in extracurricular activity / Atividade física diária em crianças participantes de atividade extrecurricular

ABSTRACT This study aimed to verify and compare the physical activity practices of children enrolled and non-enrolled on different days of week in a specific program offered at school. Seventy-eight children comprised two groups: children with extra physical activity (EPA; n=39; 15 females and 24 males; age: 9.2±0.8 years) and those with no involvement in extra physical activity (NPA; n=39; 21 females and 18 males; age: 9.0±0.4 years). To infer caloric expenditure, number of steps per day, and total distance traveled, children were monitored with pedometers during three nonconsecutive days: a day with a physical education class at school, a normal activity weekday, and a weekend day. Children enrolled in extra activities at school presented higher levels of caloric expenditure (EPA=132±61, NPA=61±25), performed more steps per day (EPA=7742±2473, NPA=5245±2306) and traveled longer distances (EPA=4201±1318, NPA=2799±1269), with boys (calories=154.1±91.6; steps=9763±3804; traveled distance=5114±2205) more active than girls (calories=94.4±46.7; steps=6691±2394; traveled distance=3726±1387). In the extracurricular physical activity day, children expended more calories (155.8±88.3), performed mores steps (10133±3724) and traveled longer distance (5442±2118) than in the physical education day (calories=127.2±79.3; steps=8409±3283; traveled distance=4478±1864) and in the weekend (calories=96.8±58.8; steps=6493±2687; traveled distance=3500±1466). Extracurricular physical activity at school leads to an increase of physical activity of boys and girls, even on days when the extracurricular activity is not offered.

RESUMO O objetivo deste estudo foi verificar e comparar a prática de atividade física de crianças em diferentes dias da semana envolvidas e não envolvidas em um programa de atividade física extracurricular. Setenta e oito crianças formaram dois grupos: crianças com atividade física extracurricular (CAF; n=39; 15 meninas e 24 meninos; idade: 9,2±0,8 anos) e crianças sem atividade física extracurricular (NAF; n=39; 21 meninas e 18 meninos; idade: 9,0±0,4 anos). Foram estimados o dispêndio calórico, o número de passos por dia e a distância percorrida, por meio de pedômetros em dias não consecutivos: um dia com aula de educação física, um dia com atividades cotidianas e um dia de final de semana. Crianças envolvidas em atividades extracurriculares na escola apresentaram maior dispêndio calórico (CAF=132±61, NAF=61±25), número de passos (CAF=7742±2473, NAF=5245±2306) e distância percorrida (CAF=4201±1318, NAF=2799±1269), sendo ainda meninos (calorias=154,1±91,6; passos=9763±3804; distância=5114±2205) mais ativos que meninas (calorias=94,4±46,7; passos=6691±2394; distância=3726±1387). No dia de atividade extracurricular, crianças dispendem mais calorias (155,8±88,3), realizam mais passos (10133±3724) e percorrem maior distância (5442±2118) do que nos dias de educação física (calorias=127,2±79,3; passos=8409±3283; distância=4478±1864) e final de semana (calorias=96,8±58,8; passos=6493±2687; distância=3500±1466). Atividade física extracurricular na escola promove aumento de atividade física de meninos e meninas, mesmo nos dias em que a atividade física extracurricular não foi oferecida.

A multiple domain postural control assessment in people with Parkinson's disease: traditional, non-linear, and rambling and trembling trajectories analysis.

BACKGROUND: Postural impairment is one of the most debilitating symptoms in people with Parkinson's disease (PD), which show faster and more variable oscillation during quiet stance than neurologically healthy individuals. Despite the center of pressure parameters can characterize PD's body sway, they are limited to uncover underlying mechanisms of postural stability and instability. RESEARCH QUESTION: Do a multiple domain analysis, including postural adaptability and rambling and trembling components, explain underlying postural stability and instability mechanisms in people with PD? METHOD: Twenty-four individuals (12 people with PD and 12 neurologically healthy peers) performed three 60-s trials of upright quiet standing on a force platform. Traditional and non-linear parameters (Detrended Fluctuation Analysis- DFA and Multiscale Entropy- MSE) and rambling and trembling trajectories were calculated for anterior-posterior (AP) and medial-lateral (ML) directions. RESULTS: PDG's postural control was worse compared to CG, displaying longer displacement, higher velocity, and RMS. Univariate analyses revealed largely longer displacement and RMS only for the AP direction and largely higher velocity for both AP and ML directions. Also, PD individuals showed lower AP complexity, higher AP and ML DFA, and increased AP and ML displacement, velocity, and RMS of rambling and trembling components compared to neurologically healthy individuals. SIGNIFICANCE: Based upon these results, people with PD have a lower capacity to adapt posture and impaired both rambling and trembling components compared to neurologically healthy individuals. These findings provide new insights to explain the larger, faster, and more variable sway in people with PD.

Haptic Information Improvement on Postural Sway is Information-Dependent But Not Influenced by Cognitive Task.

Young adults reduce their sway in both light touch (LT) and anchor systems (AS), however, the cognitive involvement in these tasks is unknown. This study investigated postural control in young adults standing upright using either LT or AS, concomitantly with a cognitive task (counting). Nine adults (26 ± 7.4 years) stood in the upright tandem stance with eyes closed, with/without LT, AS (force <2 N), and a cognitive task. The mean sway amplitude of the trunk, right wrist, and shoulder ellipse area, as well as the mean force during LT and AS were obtained. The cognitive task did not influence the magnitude of trunk sway or the mean force in the LT and AS conditions. The trunk sway magnitude was reduced in the AS and even further in LT. Wrist and shoulder variability was larger in the AS than in the LT. Based on these results, we conclude that enhanced sensory cues provided by LT and AS reduce trunk sway with little or no attentional demands.

Performance of postural balance in children and adolescents living with and without HIV.

RESEARCH QUESTION: The present study aimed to compare the postural control of children and adolescents with and without Human Immunodeficiency Virus (HIV). METHODS: A total of 32 children and adolescents (18 with HIV and 14 without) of both sexes, aged 6-18 years, were included in the present study. Participants in the HIV + group were infected through vertical transmission and received antiretroviral therapy. Participants maintained an erect, bipedal posture in the following conditions: with vision, without vision, and on a foam base. RESULTS: Concerning the evaluation of time variables, higher values ​​were observed in the HIV + group for mean anterior-posterior (AP) velocity, mean medial-lateral (ML) velocity, AP perimeter (p = 0.001), and ML perimeter (p = 0.001). Concerning the evaluation of conditions, a difference was observed in the mean AP mean sway amplitude (MSA) (p = 0.039), as the AP MSA was lower with vision than without vision or with foam. Concerning the evaluation of spectral domain variables, higher values ​​were observed in the HIV+ group for the predominant ML frequency (p = 0.04) and mean AP (p = 0.001) and ML frequencies (p = 0.001). Regarding the evaluation of conditions, a difference was found only in the predominant AP frequency (p = 0.001). Higher values ​​were found in the closed eye condition than in with foam (Δ = +103 %). CONCLUSION: The results of the present study indicated that children and adolescents living with HIV have poorer postural control performance than those without HIV.

Behavioral synergic relations between eye and postural movements in young adults searching to locate objects in room inside houses.

During precise gaze shifts, eye, head, and body movements exhibit synergic relations. In the present study, we tested the existence of behavioural synergic relations between eye and postural movements in a goal-directed, precise, visual search task (locate target objects in large images). More precisely, we tested if postural control could be adjusted specifically to facilitate precise gaze shifts. Participants also performed a free-viewing task (gaze images with no goal) and a fixation task. In both search and free-viewing tasks, young participants (n = 20; mean age = 22 years) were free to move their eyes, head, and body segments as they pleased to self-explore the images with no external perturbation. We measured eye and postural kinematic movements. The results showed significant negative correlations between eye and postural (head and upper back) movements in the precise task, but not in the free-viewing task. The negative correlations were considered to be stabilizing and synergic. Indeed, the further the eyes moved, the more postural variables were adjusted to reduce postural sway. These results suggest that postural control was adjusted to succeed in subtle and active self-induced precise gaze shifts. Furthermore, partial correlations showed significant relations between (1) task performance to find target objects and (2) synergic relations between eye and postural movements. These later results tend to show that synergic eye-postural relations were performed to improve the task performance in the precise visual task.

Compensatory Strategies Due to Knee Flexion Constraint during Gait of Non-Disabled Adults.

Constraining knee flexion of non-disabled individuals could further our understanding regarding the importance of knee joint during gait, which is a common disturbance in individuals with gait impairment. In this study we investigated whether a mechanical constraint of knee flexion in non-disabled adults would lead to compensatory strategies. Eleven non-disabled male adults walked without and with an orthosis that permitted full extension and limited knee flexion up to either 45° or 30°. We analyzed the temporal organization of lower limb kinematics and electromyograms of the rectus femoris, vastus medialis and lateralis, tibialis anterior, semitendinosus, biceps femoris, and gastrocnemius medialis and lateralis. Non-disabled adults compensated for the reduced knee flexion by increasing hip and ankle joint excursions and ankle flexor activation amplitude. Also, these adults shortened pre-swing and lengthened swing duration in the constrained limb and increased the activity of bifunctional hip extensor and knee flexor muscles in the constrained limb in relation to the unconstrained limb. The use of an orthosis that limited knee flexion in non-disabled adults leaded to compensatory strategies in the temporal organization of joint excursions and muscle activations in the constrained limb. The compensatory effects were correlated with the extent of knee flexion constraint.

Saccadic eye movement performance reduces visual manipulation influence and center of pressure displacements in older fallers.

This study examined changes in postural control and gaze performance of faller and non-faller older adults under conditions of visual tasks and optical flow manipulations. Fifteen older non-fallers (69.8 years, ± 3.2) and fifteen older fallers (71.1 years, ± 6.4) stood on a force platform inside a moving room wearing an eye tracker. Four tasks were performed: gaze fixation; predictable saccades; unpredictable saccades; and free-viewing. The stimuli appeared at a frequency of 1.1 Hz during conditions of predictable and unpredictable saccades. Sixteen trials were divided into two blocks. In the first block, the room remained stationary. In the second block, the room oscillated, without the participant's awareness, with a 0.6 cm amplitude and 0.2 Hz frequency. Results showed postural sway attenuation in older fallers during the saccadic tasks compared to gaze fixation and free-viewing tasks, in both stationary and moving room conditions. Both groups showed increased center of pressure (CoP) magnitude during the moving room condition and CoP displacements strongly coupled to the room's movement. The influence of the moving room on the postural sway was reduced during the saccadic tasks for both older groups. Older fallers exhibited higher variability compared to older non-fallers. Gaze behavior differences between groups were dependent on the goals of the visual tasks. Therefore, CoP displacements of older adults are reduced during saccadic tasks regardless of their falling history. However, postural and gaze performance of older fallers suggests increased deterioration of postural and oculomotor control which may be used as a predictor of fall risk.

Trunk and head displacements stabilized to perform both horizontal and vertical saccadic eye movements.

Vision is crucial for humans to interact with their surrounding environment, and postural sway is reduced to allow short eye movements. However, the extent of subtle changes in postural control for horizontal and vertical eye movements remains unclear. The goal of this study was to investigate the effects of vertical and horizontal eye movements on head and trunk control in young adults. Fifteen healthy adults (23.4 ± 4.7 years) stood upright in three conditions for 60 s: fixation, horizontal, and vertical guided eye movements. In fixation, participants had to fixate on a stationary target. In both the horizontal and vertical eye movements, the target was presented with a frequency of 0.5 Hz and a visual angle of 11°. Eye displacement was monitored using a SMI eye tracker (ETG2.0) and trunk and head sway were monitored using infrared markers (Optotrak 3020, NDI). The mean sway amplitude was lower in both directions for eye movements and lowest in the vertical direction compared to the fixation condition. The sway area was also lower in vertical eye movement than in the fixation condition. We also found that the sway reduction was greater at head than at trunk level. The median frequency sway in the anterior-posterior direction was higher in both eye movements than in fixation. Based upon these results, we suggest that to perform short eye movements, postural sway is more strongly controlled at the head level than at the trunk and in vertical eye movements than in horizontal movements.

Variability of visually-induced center of pressure displacements is reduced while young adults perform unpredictable saccadic eye movements inside a moving room.

This study investigated the modulation of center of pressure (CoP) displacements of young adults as they performed predictable and unpredictable saccadic eye movements in stationary and moving visual scenarios. We also examined whether the relationship between CoP displacements and visual stimulus, provided by the moving scenario, and gaze control itself, are affected by the demands of the saccadic tasks. Fifteen young adults (20.53 ± 2.1 years old) stood upright on a force plate, inside a moving room, wearing an eye tracker while performing three tasks: gaze fixation (fixating on a target in the center of the screen), predictable task (saccades while following a target which continuously appeared and disappeared on the right and left sides), and unpredictable task (similar to the previous task, but the participants did not know which side the target would appear on). For saccadic tasks, the target appeared at a frequency of 1.1 Hz and with eccentricity of 11.5 degrees of visual angle. Two blocks of six trials were performed: in the first block, the room remained stationary and in the second, it oscillated (0.6 cm amplitude; 0.2 Hz frequency). Mean amplitude of CoP displacements was lower in the saccadic tasks compared to the gaze fixation, in both conditions; and higher in the moving scenario than in the stationary condition. Variability of CoP displacements was lower in the unpredictable saccades than gaze fixation task. Saccade reaction time was longer in the unpredictable than predictable task. We conclude that CoP displacements are reduced to facilitate performance of the saccadic tasks regardless of conditions and task complexity. Furthermore, lower variability suggests modulation of CoP displacements to deal with the increased attentional demands associated with the performance of the unpredictable saccades, indicating the important role of visual task constraints in postural control.

Effects of limited knee flexion movement in intra-limb gait coordination.

This study aimed to investigate intra-limb coordination in non-disabled individuals walking with and without a constrained knee and in individuals with stroke. We hypothesized that a constrained knee would modify the intra-limb coordination of non-disabled individuals and that non-disabled individuals walking with a constrained knee would present coordination patterns similar to those presented by individuals with stroke. Twelve individuals with chronic stroke (age: 54.1 ± 9.9 years) and 12 age- and sex-matched individuals (age: 54.8 ± 9.2 years) with no known gait impairment (non-disabled individuals) participated in this study. Non-disabled individuals walked with and without an orthosis on one of their knees, limiting flexion to 40°, which was the average maximum knee flexion presented by the participants with stroke. Lower limb coordination was assessed on the basis of vector coding for the thigh-shank and shank-foot couplings during stance and swing periods of gait. Constrained knee flexion in non-disabled individuals mainly affected the thigh-shank coupling but not the shank-foot coupling of the constrained limb. There was reduced anti-phase coordination during the stance and swing periods and a marked increase in in-phase coordination during the swing period. Non-disabled individuals presented most changes toward the coordination pattern presented by individuals with stroke, except for the thigh-phase mode during the swing period, which was lower than that in individuals with stroke. Reduced knee flexion movement caused similar alterations in the intra-limb coordination pattern in non-disabled individuals compared to those observed in individuals with stroke. Therefore, diminished knee flexion movement, which is presented by individuals with stroke, can be considered a key disturbance that leads to impairment in lower extremity intra-limb coordination.

Gait alterations induced by unloaded body weight in individuals with stroke while walking on moveable and fixed surfaces.

This study examined the effects of the support surface (i.e., treadmill or ground) and the quantity of body weight unloading provided by a partial body weight support (PBWS) system on the spatiotemporal gait characteristics of individuals with stroke. Fifteen individuals, aged 57.2 ± 9.8 years, with chronic stroke walked on a treadmill and on the ground with 0%, 10%, and 20% of PBWS. Inertial sensors placed on the participants' feet registered 3-D acceleration and 3-D angular velocity during walking, and some gait parameters were calculated. Overall, individuals with stroke walked with shorter and slower strides and spent more time in contact with the support surface when walking on the treadmill compared to when walking on the ground. The duration of double limb support decreased when the percentage of PBWS increased. Stride length and speed were more variable in the paretic limb than in the non-paretic limb. Treadmill walking was more consistent and less similar to ordinary walking than walking on the ground. The gait pattern of individuals with stroke was modulated according to the support surface on which walking was performed, and the use of a PBWS system seems suitable to develop walking proficiencies on a daily basis.

Health Issues Due to the Global Prevalence of Sedentariness and Recommendations towards Achieving a Healthier Behaviour.

Sedentariness has progressed in recent years. Here, we summarize the high prevalence of objectively measured sedentariness and the list of health problems associated with sedentariness. According to the literature, a minimum sedentary time of 8 h/d may avoid the harmful effects of sedentariness. Our review of the literature shows that many countries worldwide exceed this threshold. The coronavirus disease 2019 pandemic has increased the proportion of time spent seated in chairs and/or other types of furniture. Furthermore, prolonged sedentariness will continue to increase because it is assumed that people, at least those in desk jobs, perform their work better when sitting than when standing. Many practical solutions should be implemented to help people reduce their sedentary time. People need to be aware that prolonged sedentariness causes health problems. They need to measure the amount of time spent being sedentary to self-guide their behaviour. They should adopt a new lifestyle to avoid prolonged sedentariness and prolonged standing. In addition, we point out that they should frequently change their posture to avoid fatigue and health issues. For global public health, there is an urgent need to adopt an intermediate healthy/healthier behaviour between too much time spent in the sitting and standing positions.

Optimization of postural control in precise gaze shifts and laser pointing.

Young adults are known to reduce their postural sway to perform precise visual search and laser pointing tasks. We tested if young adults could reduce even more postural and/or center of pressure sway to succeed in both tasks simultaneously. The methodology is novel because published pointing tasks usually require continuously looking at the pointed target and not exploring an image while pointing elsewhere at the same time. Twenty-five healthy young adults (23.2 ± 2.5 years) performed six visual tasks. In the free-viewing task, participants randomly explored images with no goal. In two visual search tasks, participants searched to locate objects (easy search task) or graphical details (hard search task). Participants additionally pointed a laser beam into a central circle (2°) or pointed the laser turned off. Postural sway and center of pressure sway were reduced complementarily - in various variables - to perform the visual search and pointing tasks. Unexpectedly, the pointing task influenced more strongly postural sway and center of pressure sway than the search tasks. Overall, the participants adopted a functional strategy in stabilizing their posture to succeed in the pointing task and also to fully explore images. Therefore, it is possible to inverse the strength of effects found in the literature (usually stronger for the search task) in modulating the experimental methodology. In search tasks more than in free-viewing tasks, participants mostly rotated their eyes and head, and not their full body, to stabilize their posture. These results could have implications for shooting activities, video console games and rehabilitation most particularly.