Postural instability in Parkinson’s disease (PD) is characterized by impaired postural responses to transient perturbations, increased postural sway in stance and difficulty transitioning between tasks. In addition, some studies suggest that loss of dopamine in the basal ganglia due to PD results in difficulty using proprioceptive information for motor control. Here, we quantify the ability of subjects with PD and age-matched control subjects to use and re-weight sensory information for postural control during steady-state (...) conditions of continuous rotations of the stance surface or visual surround. We measure the postural sway of subjects in response to a pseudorandom, surface-tilt stimulus with eyes closed, and in response to a pseudorandom, visual-tilt stimulus. We use a feedback control model of the postural control system to interpret our results, focusing on sensory weighting as a function of stimulus amplitude. We find that subjects with PD can re-weight their dependence upon sensory information in response to changes in surface- or visual-stimulus amplitude. Specifically, subjects with PD behaved like age-matched control subjects by decreasing proprioceptive contribution to stance control with increasing surface-tilt amplitude, and decreasing visual contribution with increasing visual-tilt amplitude. However, subjects with PD do not decrease their reliance on proprioception as much as age-matched controls for small increases in surface-stimulus amplitudes. Levodopa medication did not affect sensory re-weighting behaviors for postural control. The impairment in PD subject’s ability to respond differently to small changes in surface rotation amplitudes is consistent with an increased threshold for perceiving proprioceptive signals, which may result from decreased signal-to-noise in the dopaminergic pathways associated with sensory processing and/or sensory integration. (shrink)

Fundamental movement skill proficiency does not develop solely due to maturation, but also via diverse perceptual-motor experiences across childhood. Practicing gymnastics has been shown to improve postural control. The purpose of the present study was to examine potential changes to postural control of children following a course of educational gymnastics. Two groups of children both completed 20 × 45-min physical education lessons; one group completed educational gymnastics lessons in school delivered by a professional coach, the other (...) group completed their typical PE classes. Unipedal balancing performance was assessed by calculating the percentage of successful trials made. Postural sway dynamics were explored by calculating center-of-pressure sample entropy, 95% ellipse sway area and sway velocity. Measurements were taken before the lessons began and immediately after the lessons were completed. The gymnastics group performed better than the typical PE group at unipedal balancing. Females outperformed males in both groups. Males made different changes to postural control compared to females across 3 months. Educational gymnastics enabled children in a critical period of development to make more rapid improvements to postural performance and control. Novel movement experiences, like those offered by educational gymnastics, may have a positive influence on postural control and importantly, physical literacy. Future work should examine how sex effects the development of postural control strategies in young children. (shrink)

Dual task is known to affect postural stabilty in children. We explored the effect of visual tasks on postural control in dyslexic and in age-matched non-dyslexic children. Thirty dyslexic children (mean age: 9.80 ± 0.28 years) were compared with thirty non-dyslexic children (mean age: 9.92 ± 0.35 years). All children underwent ophthalmologic and optometric evaluation. Eye movements were recorded by a video-oculography system (EyeBrain ® T2) and postural sway was recorded simultaneously by a force platform (TechnoConept®). (...) Both groups of children performed fixations, pursuits, pro- and anti-saccades tasks. Dyslexic children showed significantly poor near fusional vergence ranges (convergence and divergence) with respect to the non-dyslexic children. During the postural task, quality of fixation and anti-saccade performance in dyslexic children were significantly worse compared to non-dyslexic children. In contrast, the number of catch-up saccades during pursuits and the latency of pro-and anti-saccades were similar in both groups of children examined. Concerning postural quality, dyslexic children were more unstable than age-matched non-dyslexic children. For both groups of children tested we also observed that executing saccades (pro- and anti-saccades) reduced postural values significantly in comparison with fixation and pursuit tasks. The impairment in convergence and divergence fusional capabilities could be due to an immaturity in cortical structures controlling the vergence system. The poor oculomotor performance reported in dyslexic children suggested a deficit in allocating visual attention and their postural instability observed is in line with the cerebellar impairment previously reported in dyslexic children. Finally, pro- or anti-saccades reduce postural values compared to fixation and pursuit tasks in both groups of children tested, suggesting a different influence of visual tasks on postural control according to their attentional demand. (shrink)

The visual system is a source of sensory information that perceives environmental stimuli and interacts with other sensory systems to generate visual and postural responses to maintain postural stability. Although the three sensory systems; the visual, vestibular, and somatosensory systems work concurrently to maintain postural control, the visual and vestibular system interaction is vital to differentiate self-motion from external motion to maintain postural stability. The visual system influences postural control playing a key role (...) in perceiving information required for this differentiation. The visual system’s main afferent information consists of optic flow and retinal slip that lead to the generation of visual and postural responses. Visual fixations generated by the visual system interact with the afferent information and the vestibular system to maintain visual and postural stability. This review synthesizes the roles of the visual system and their interaction with the vestibular system, to maintain postural stability. (shrink)

Inter-limb asymmetries are associated with a higher potential risk for non-contact injuries. Differences in function or performance between the limbs might lead to imbalances and promote instability, increasing the potential risk for injuries. Consequently, an investigation of inter-limb asymmetries should be included in injury risk assessment. Furthermore, since non-contact injuries mainly occur under loaded conditions, an investigation of load-induced changes of inter-limb asymmetries can provide additional information on the athlete’s potential injury risk. Therefore, the current study aimed to investigate the (...) influence of physical load on inter-limb asymmetries in dynamic postural control, which is essential in situations with a high risk for non-contact injuries such as landing, cutting, or stopping. In total, dynamic postural control of 128 active and healthy subjects was examined. Dynamic postural control was tested with the Y-Balance Test before and after a loading protocol on a bicycle ergometer or a treadmill. The results showed no significant increase of the inter-limb asymmetries in anterior direction [F = 4.44, p = 0.04, η2p = 0.03]. Moreover, there is high variation between the subjects regarding the magnitude and the direction of the asymmetries and the changes due to load. Therefore, a more individual analysis considering the magnitude and the direction of the asymmetries is required. Thereby, considering different modifying factors, e.g., sex, injury history, and baseline level of asymmetries, can be helpful. Moreover, an analysis of the changes during load might provide further insights, reveal possible differences, and help detect the reasons and mechanisms underlying inter-limb asymmetries and asymmetrical loading. (shrink)

Virtual reality enables individuals to be exposed to naturalistic environments in laboratory settings, offering new possibilities for research in human neuroscience and treatment of mental disorders. We used VR to study psychological, autonomic and postural reactions to heights in individuals with varying intensity of fear of heights. Study participants were immersed in a VR of an unprotected open-air elevator platform in an urban area, while standing on an unstable ground. Virtual elevation of the platform elicited robust and reliable psychophysiological (...) activation including increased distress, heart rate, and electrodermal activity, which was higher in individuals suffering from fear of heights. In these individuals, compared with individuals with low fear of heights, the VR height exposure resulted in higher velocity of postural movements as well as decreased low-frequency body sway oscillations. This indicates that individuals with strong fear of heights react to heights with maladaptive rigidity of posture due to increased weight of visual input for balance control, while the visual information is less reliable at heights. Our findings show that exposure to height in a naturalistic VR environment elicits a complex reaction involving correlated changes of the emotional state, autonomic activity, and postural balance, which are exaggerated in individuals with fear of heights. (shrink)

A classical theoretical frame to interpret motor reactions to emotional stimuli is that such stimuli, particularly those threat-related, are processed preferentially, i.e., they are capable of capturing and grabbing attention automatically. Research has recently challenged this view, showing that the task relevance of emotional stimuli is crucial to having a reliable behavioral effect. Such evidence indicated that emotional facial expressions do not automatically influence motor responses in healthy young adults, but they do so only when intrinsically pertinent to the ongoing (...) subject’s goals. Given the theoretical relevance of these findings, it is essential to assess their generalizability to different, socially relevant emotional stimuli such as emotional body postures. To address this issue, we compared the performance of 36 right-handed participants in two different versions of a Go/No-go task. In the Emotional Discrimination task, participants were required to withhold their responses at the display of emotional body postures and to move at the presentation of neutral postures. Differently, in the control task, the same images were shown, but participants had to respond according to the color of the actor/actress’ t-shirt, disregarding the emotional content. Results showed that participants made more commission errors for happy than fearful body postures in the Emotional Discrimination task. However, this difference disappeared in the control task. Such evidence indicates that, like facial emotion, emotional body expressions do not influence motor control automatically, but only when they are task-relevant. (shrink)

Previous works usually report greater postural stability in precise visual tasks than in stationary-gaze tasks. However, existing cognitive models do not fully support these results as they assume that performing an attention-demanding task while standing would alter postural stability because of the competition of attention between the tasks. Contrary to these cognitive models, attentional resources may increase to create a synergy between visual and postural brain processes to perform precise oculomotor behaviors. To test this hypothesis, we investigated (...) a difficult searching task and a control free-viewing task. The precise visual task required the 16 young participants to find a target in densely furnished images. The free-viewing task consisted of looking at similar images without searching anything. As expected, the participants exhibited significantly lower body displacements and a significantly higher cognitive workload in the precise visual task than in the free-viewing task. Most important, our exploration showed functional synergies between visual and postural processes in the searching task, that is, significant negative relationships showing lower head and neck displacements to reach more expended zones of fixation. These functional synergies seemed to involve a greater attentional demand because they were not significant anymore when the cognitive workload was controlled. In the free-viewing task, only significant positive relationships were found and they did not involve any change in cognitive workload. An alternative cognitive model and its potential subtended neuroscientific circuit are proposed to explain the supposedly cognitively grounded functional nature of vision–posture synergies in precise visual tasks. (shrink)

Felicitas Goodman (1990) observed that naive participants experienced unique trance states, characterized by specific visionary content, when they assumed particular postures and listened to monotonous rattling. Students (n = 284), enrolled in various sections of the course Introduction to Psychology, experienced one of four conditions with their eyes closed: Sitting Quietly with and without Drumming, Standing (Feather Serpent) Posture plus Drumming with and without Suggested Experiences. Participants completed the Phenomenology of Consciousness Inventory (Pekala 1982, 1991c) and wrote narratives following their (...) respective stimulus conditions. Participants reported less imagery, joy, and absorption, but more internal dialogue, self‐awareness, and muscular tension in the posture, compared to the sitting quietly, conditions. Goodman's results of specific posture (content‐related) effects with naive participants were not replicated. (shrink)

IntroductionAlthough a few studies suggest that young overweight to obese children and adolescents may have impaired postural control compared to young normal-weight peers, little information exists about how these two groups differ in the quality of the underlying balance strategies employed. Hence, the aim of the present study was a first comprehensive examination of the structural complexity of postural sways in these two cohorts during quiet bilateral standing.MethodsNineteen YO secondary school students were carefully matched to YN controls (...) for age, sex, height, and school. Mediolateral and anteriorposterior acceleration signals were recorded with an inertial measurement unit positioned at the trunk while standing barefoot in two conditions: firm and foam support surface. The magnitude of postural fluctuations was obtained using the root mean square. The temporal structure of the signals was analyzed via sample entropy, largest Lyapunov exponent, and detrended fluctuation analysis algorithm. Reliability was assessed using a test–retest design.ResultsIn both groups, foam standing caused higher postural fluctuations and reduced structural complexity. In comparison to YN, YO exhibited a higher RMSAP. Especially in ML direction, the acceleration signals of the YO had higher repeatability, greater long-range correlations, and lower local stability. However, these observations were largely independent of the task difficulty. Except for α-DFAAP, the IMU approach proved reliable to characterize posture control.DiscussionOur outcomes confirm postural control deficits in YO compared to their YN peers and indicate impaired regulatory mechanisms reflected as rigidity. Such less complex patterns usually reflect diverse pathologies, are detrimental to compensate for internal or external perturbations, and are attributed to lower adaptability and task performance. Without targeted balance stimuli, YO likely end in a lifelong vicious circle of mutually dependent poor balance regulation and low physical activity. (shrink)

Postural instability and balance impairment are disabling symptoms in patients with acute unilateral peripheral vestibular hypofunction. Vestibular rehabilitation is known to improve the vestibular compensation process, but its effect on posture recovery remains poorly understood, little is known about when VR must be done, and whether the degree of vestibular loss matters is uncertain. We analyzed posture control under static and dynamic postural tasks performed in different visual conditions [eye open ; eyes closed ; and optokinetic stimulation] (...) using dynamic posturography. Non-linear analyses of the postural performance were performed in two groups of patients with UVH subjected to the same VR program based on the unidirectional rotation paradigm and performed either early or later after vertigo attack. Distribution of the angular horizontal vestibulo-ocular reflex gain values recorded on the hypofunction side before rehabilitation differentiated two distinct sub-groups with aVOR gains below or above 0.20. The postural performance of the four sub-groups of patients with UVH tested before VR showed significantly altered postural parameters compared with healthy controls. Greater instability, higher energy to control posture, larger sway without feedback corrections, and lower time of automatic control of posture were observed in static conditions. The four sub-groups recovered near-normal postural performance after VR in the EO and EC conditions, but still exhibited altered postural performance with optokinetic stimulation. In dynamic posturography conditions and before VR, the percentage of patients able to perform the postural tasks with EC and optokinetic stimulation was significantly lower in the two sub-groups with aVOR gain <0.20. After VR, the improvement of the postural parameters depended on the stage of rehabilitation and the degree of vestibular hypofunction. The best balance function recovery was found in the sub-group with early VR and pre-rehabilitation aVOR gain above 0.20, the worst in the sub-group with late rehabilitation and aVOR gain below 0.20. These differences were seen when the vestibular input remains the main sensory cue to control balance, that is, on unstable support without vision or altered visual motion cues. These findings extend to dynamic balance recovery the crucial roles of early rehabilitation and degree of vestibular hypofunction which we have already highlighted for vestibulo-ocular reflex recovery. (shrink)

Objective: Stand-to-sit task is an important daily function, but there is a lack of research evidence on whether knee osteoarthritis affects the postural balance during the task. This study aimed to compare individuals with knee OA and asymptomatic controls in postural balance and identify kinematic and lower extremity muscle activity characteristics in individuals with knee OA during the stand-to-sit task.Methods: In total, 30 individuals with knee OA and 30 age-matched asymptomatic controls performed the 30-s Chair Stand Test at (...) self-selected speeds. Motion analysis data and surface electromyography were collected while participants performed the 30sCST. To quantify postural balance, the displacement of the center of mass and the peak instantaneous velocity of the CoM were calculated. The kinematic data included forward lean angles of the trunk and pelvic, range of motion of the hip, knee, and ankle joints in the sagittal plane. The averaged activation levels of gluteus maximus, vastus lateralis, vastus medialis, rectus femoris, biceps femoris, tibialis anterior, and medial head of gastrocnemius muscles were indicated by the normalized root mean square amplitudes.Results: Compared with the asymptomatic control group, the knee OA group prolonged the duration of the stand-to-sit task, demonstrated significantly larger CoM displacement and peak instantaneous CoM velocity in the anterior-posterior direction, reduced ankle dorsiflexion RoM, greater anterior pelvic tilt RoM, and lower quadriceps femoris and muscles activation level coupled with higher BF muscle activation level during the stand-to-sit task.Conclusion: This study indicates that individuals with knee OA adopt greater pelvic forward lean RoM and higher BF muscle activation level during the stand-to-sit task. However, these individuals exist greater CoM excursion in the anterior-posterior direction and take more time to complete the task. This daily functional activity should be added to the rehabilitation goals for individuals with knee OA. The knee OA group performs reduced ankle dorsiflexion RoM, quadriceps femoris, and TA activation deficit. In the future, the rehabilitation programs targeting these impairments could be beneficial for restoring the functional transfer in individuals with knee OA. (shrink)

Multiple sensory signals from visual, somatosensory and vestibular systems are used for human postural control. To maintain postural stability, the central nervous system keeps the center of mass (CoM) within the base of support. The influence of the stomatognathic motor system on postural control has been established under static conditions, but it has not yet been investigated during dynamic steady-state balance. The purpose of the study was to investigate the effects of controlled stomatognathic motor activity (...) on the control and stability of the CoM during dynamic steady-state balance. A total of 48 physically active and healthy adults were assigned to three groups with different stomatognathic motor conditions: jaw clenching, tongue pressing and habitual stomatognathic behavior. Dynamic steady-state balance was assessed using an oscillating platform and the kinematic data were collected with a 3D motion capturing system. The path length (PL) of the 3D CoM trajectory was used for quantifying CoM sway. Temporal dynamics of the CoM movement was assessed with a detrended fluctuation analysis (DFA). An uncontrolled manifold (UCM) analysis was applied to assess the stability and control of the CoM with a subject-specific anthropometric 3D model. The statistical analysis revealed that the groups did not differ significantly in PL, DFA scaling exponents or UCM parameters. The results indicated that deliberate jaw clenching or tongue pressing did not seem to affect the sway, control or stability of the CoM on an oscillating platform significantly. Because of the task-specificity of balance, further research investigating the effects of stomatognathic motor activities on dynamic steady-state balance with different movement tasks are needed. Additionally, further analysis by use of muscle synergies or co-contractions may reveal effects on the level of muscles, which were not visible on the level of kinematics. This study can contribute to the understanding of postural control mechanisms, particularly in relation to stomatognathic motor activities and under dynamic conditions. (shrink)

ObjectiveAre people with a characteristically large physiological sway rendered particularly unstable when standing on a moving surface? Is postural sway in standing individuals idiosyncratic? In this study, we examine postural sway in individuals standing normally, and when subtle continuous sinusoidal disturbances are applied to their support platform. We calculate consistency between conditions to verify if sway can be considered characteristic of each individual. We also correlate two different aspects of participants’ responses to disturbance; their sway velocity and their (...) regulation of body orientation.MethodsNineteen healthy adults (age 29.2 ± 3.2 years) stood freely on footplates coaxially aligned with their ankles and attached to a motorized platform. They had their eyes closed, and hips and knees locked with a light wooden board attached to their body. Participants either stood quietly on a fixed platform or on a slowly tilting platform (0.1 Hz sinusoid; 0.2 and 0.4 deg). Postural sway size was separated into two entities: (1) the spontaneous sway velocity component (natural random relatively rapid postural adjustments, RMS body angular velocity) and (2) the evoked tilt gain component (much slower 0.1 Hz synchronous tilt induced by the movement of the platform, measured as peak-to-peak (p-p) gain, ratio of body angle to applied footplate rotation).ResultsThere was no correlation between the velocity of an individual’s sway and their evoked tilt gain (r= 0.34,p= 0.15 andr= 0.30,p= 0.22). However, when considered separately, each of the two measurements showed fair to good absolute agreement within conditions. Spontaneous sway velocity consistently increased as participants were subjected to increasing disturbance. Participants who swayed more (or less) did so across all conditions [ICC(3,k)= 0.95]. Evoked tilt gain also showed consistency between conditions [ICC(3,k)= 0.79], but decreased from least to most disturbed conditions.ConclusionThe two measurements remain consistent between conditions. Consistency between conditions of two very distinct unrelated measurements reflects the idiosyncratic nature of postural sway. However, sway velocity and tilt gain are not related, which supports the idea that the short-term regulation of stability and the longer-term regulation of orientation are controlled by different processes. (shrink)

The review adresses the relationship between sport expertise (i.e., sport competition level), postural performance (amount of motion of the centre of mass/of pressure of foot or ability to preserve body balance) and postural strategy (geometric organization of different body segments as well as neurobiological involvement of organism). Since the conditions of postural evaluation are likely to influence results, the aim is to compare athletes at different competition levels in ecological postural conditions (specific postural conditions related (...) to the sport practiced) and non-ecological postural conditions (decontextualized postural conditions in relation to the sport practiced). Evidence suggests that the most successful athletes in terms of sport competition level have the best postural performance both in ecological and non-ecological postural conditions. However, in non-ecological conditions the postural tasks should be preferentially challenging or relatively close to the sport practice stance. Moreover, the most successful athletes also have more elaborate postural strategies compared with athletes at lower competition level. Mechanistic explanations as well as conceptual models are proposed to explain the role of different factors influencing the relationship between sport expertise and postural performance and strategy. (shrink)

Physical fatigue negatively affects postural control, resulting in impaired balance performance in young and older adults. Similar effects on postural control can be observed for mental fatigue mainly in older adults. Controversial results exist for young adults. There is a void in the literature on the effects of fatigue on balance and cortical activity. Therefore, this study aimed to examine the acute effects of PF and MF on postural sway and cortical activity. Fifteen healthy young (...) adults aged 28 ± 3 years participated in this study. MF and PF protocols comprising of an all-out repeated sit-to-stand task and a computer-based attention network test, respectively, were applied in random order. Pre and post fatigue, cortical activity and postural sway were tested during a challenging bipedal balance board task. Absolute spectral power was calculated for theta, alpha-2, beta-1, and beta-2 in frontal, central, and parietal regions of interest and baseline-normalized. Inference statistics revealed a significant time-by-fatigue interaction for CoPd and CoPv, and a significant main effect of time for CoP variability. Post hoc analyses showed a significant increase in CoPd and CoPv following PF but not MF. For cortical activity, a significant time-by-fatigue interaction was found for relative alpha-2 power in parietal areas. Post hoc tests indicated larger alpha-2 power increases after PF compared to MF. In addition, changes in parietal alpha-2 power and measures of postural sway did not correlate significantly, irrespective of the applied fatigue protocol. No significant changes were found for the other frequency bands, irrespective of the fatigue protocol and ROI under investigation. Thus, the applied PF protocol resulted in increased postural sway and CoP variability accompanied by enhanced alpha-2 power in the parietal ROI while MF led to increased CoP variability and alpha-2 power in our sample of young adults. Potential underlying cortical mechanisms responsible for the greater increase in parietal alpha-2 power after PF were discussed but could not be clearly identified as cause. Therefore, further future research is needed to decipher alternative interpretations. (shrink)

Postural reflexes are essential for locomotion and postural stability, and may play an important role in the etiology of chronic back pain. It has recently been theoretically predicted, and with the help of unilateral perturbations of the trunk experimentally confirmed that the sensorimotor control must lower the reflex amplitude for increasing reflex delays to maintain spinal stability. The underlying neuromuscular mechanism for the compensation of postural perturbations, however, is not yet fully understood. In this study, we (...) applied unilateral and bilateral sudden external perturbations to the trunk of healthy subjects and measured the muscular activity and the movement onset of the trunk. We found that the onset of the trunk muscle activity is prior to, or coincident with, the onset of the trunk movement. Additionally, the results of our experiments imply that the muscular response mechanism integrates distant sensory information from both sides of the body. These findings rule out a simple monosynaptic stretch reflex in favor of a more complex polysynaptic postural reflex mechanism to compensate postural perturbations. Moreover, the previously predicted negative correlation between reflex delay and reflex gain was also confirmed for bilateral perturbations. (shrink)

Body awareness refers to the individual ability to process signals originating from within the body, which provide a mapping of the body’s internal landscape and its relation with space and movement. The present study aims to evaluate psychometric properties and validate in French two self-report measures of body awareness: the Postural Awareness Scale, and the last version of the Multidimensional Assessment of Interoceptive Awareness questionnaire. We collected data in a non-clinical, adult sample using online survey, and a subset of (...) the original sample also completed the retest control. Factor analyses and reliability analyses were conducted. Construct validity of the PAS and the MAIA-2 were examined by testing their association with each other, and with self-report measures of personality, alexithymia and dispositional trait mindfulness. Factor analyses of the PAS supported the same two-factor structure as previously published versions. For the MAIA-2, factor analyses suggested that a six-factor structure, excluding Not-Worrying and Not-Distracting factors, could successfully account for a common general factor of self-reported interoception. We found satisfactory internal consistency, construct validity, and reliability over time for both the PAS and the MAIA-2. Altogether, our findings suggest that the French version of the PAS and the MAIA-2 are reliable self-report tools to assess both components of body awareness. (shrink)

ABSTRACTPrevious work has shown that a stooped posture may activate negative mood. Extending this work, the present experiments examine how stooped body posture influences recovery from pre-existing negative mood. In Experiment 1, participants were randomly assigned to receive either a negative or neutral mood induction, after which participants were instructed to take either a stooped, straight, or control posture while writing down their thoughts. Stooped posture led to less mood recovery in the negative mood condition, and more negative mood (...) in the neutral mood condition. Furthermore, stooped posture led to more negative thoughts overall compared to straight or control postures. In Experiment 2, all participants underwent a negative mood induction, after which half received cognitive reappraisal instructions and half received no instructions. Mood-congruent cognitions were assessed through autobiographical memory recall. Again, stooped position led to less mood recovery. Notably, this was independent of regulation instruction. These findings demonstrate for the first time that posture plays an important role in recovering from negative mood. (shrink)

ObjectiveThe aim of our study was to investigate abnormal changes in brain activity in patients with persistent postural-perceptual dizziness using magnetoencephalography.MethodsMagnetoencephalography recordings from 18 PPPD patients and 18 healthy controls were analyzed to determine the source of brain activity in seven frequency ranges using accumulated source imaging.ResultsOur study showed that significant changes in the patterns of localization in the temporal-parietal junction were observed at 1–4, 4–8, and 12–30 Hz in PPPD patients compared with healthy controls, and changes in the (...) frontal cortex were found at 1–4, 80–250, and 250–500 Hz in PPPD patients compared with controls. The neuromagnetic activity in TPJ was observed increased significantly in 1–4 and 4–8 Hz, while the neuromagnetic activity in frontal cortex was found increased significantly in 1–4 Hz. In addition, the localized source strength in TPJ in 1–4 Hz was positively correlated with DHI score, while the localized source strength in frontal cortex in 1–4 Hz was positively correlated with HAMA score.ConclusionOur results demonstrated that alterations in the TPJ and frontal cortex may play a critical role in the pathophysiological mechanism of PPPD. The neuromagnetic activity in TPJ may be related to dizziness symptom of PPPD patients, while the neuromagnetic activity in frontal lobe may be related to emotional symptoms of PPPD patients. In addition, frequency-dependent changes in neuromagnetic activity, especially neuromagnetic activity in low frequency bands, were involved in the pathophysiology of PPPD. (shrink)

Performance and control of upright bipedal posture requires a constant and dynamic integration of relative contributions of different sensory inputs (i. e., sensory reweighting) to enable effective adaptations as individuals face environmental changes and perturbations. Children with gymnastic experience showed balance performance closer to that of adults during and after proprioceptive alteration than children without gymnastic experience when their center of pressure (COP) was analyzed. However, a particular COP sway can be achieved through performing and coordinating different postural (...) movements. The aim of this study was to assess how children and adults of different gymnastic experience perform and control postural movements while they have to adjust balance during and after bilateral tendon vibration. All participants were equipped with spherical markers attached to their skin and two vibrators strapped over the Achilles tendons. Bipedal stance was performed in three 45-s trials in two visual conditions (eyes open, EO, and eyes closed, EC) ordered randomly in which vibration lasted 10 s. Posture movements were analyzed by a principal component analysis (PCA) calculated on normalized and weighted markers coordinates. The relative standard deviation of each principal movement component (principal position, PP-rSTD) quantified its contribution to the whole postural movements, i.e., quantified the coordinative structure. The first (principal velocities, PV-rSTD) and second (principal accelerations, PA-rSTD) time-derivatives characterized the rate-dependent sensory information associated with and the neuromuscular control of the postural movements, respectively. Children without gymnastic experience showed a different postural coordinative structure and different sensory-motor control characteristics. They used less ankle movements in the anterior-posterior direction but increased ankle movements in medio-lateral direction, presented larger hip and trunk velocities, and exhibited more hip actions. Gymnastic experience during childhood seemed to benefit the development of proprioceptive reweighting processes in children, leading to a more mature form of coordinating and controlling posture similarly to adults. (shrink)

Many individuals with disabling conditions have difficulty with gait and balance control that may result in a fall. Exoskeletons are becoming an increasingly popular technology to aid in walking. Despite being a significant aid in increasing mobility, little attention has been paid to exoskeleton features to mitigate falls. To develop improved exoskeleton stability, quantitative information regarding how a user reacts to postural challenges while wearing the exoskeleton is needed. Assessing the unique responses of individuals to postural perturbations (...) while wearing an exoskeleton provides critical information necessary to effectively accommodate a variety of individual response patterns. This report provides kinematic and neuromuscular data obtained from seven healthy, college-aged individuals during posterior support surface translations with and without wearing a lower limb exoskeleton. A 2-min, static baseline standing trial was also obtained. Outcome measures included a variety of 0 dimensional measures such as center of pressure RMS, peak amplitude, velocities, pathlength, and electromyographic RMS, and peak amplitudes. These measures were obtained during epochs associated with the response to the perturbations: baseline, response, and recovery. T-tests were used to explore potential statistical differences between the exoskeleton and no exoskeleton conditions. Time series waveforms of the COP and EMG data were also analyzed. Statistical parametric mapping was used to evaluate the 1D COP and EMG waveforms obtained during the epochs with and without wearing the exoskeleton. The results indicated that during quiet stance, COP velocity was increased while wearing the exoskeleton, but the magnitude of sway was unchanged. The OD COP measures revealed that wearing the exoskeleton significantly reduced the sway magnitude and velocity in response to the perturbations. There were no systematic effects of wearing the exoskeleton on EMG. SPM analysis revealed that there was a range of individual responses; both behaviorally and among neuromuscular activation patterns. Using both the OD and 1D measures provided a more comprehensive representation of how wearing the exoskeleton impacts the responses to posterior perturbations. This study supports a growing body of evidence that exoskeletons must be personalized to meet the specific capabilities and needs of each individual end-user. (shrink)

To controlforceaccurately under a wide range of behavioral conditions, the central nervous system would either require a detailed, continuously updated representation of the state of each muscle (and the load against which each is acting) or else force feedback with sufficient gain to cope with variations in the properties of the muscles and loads. The evidence for force feedback with adequate gain or for an appropriate central representation is not sufficient to conclude that force is the major controlled variable in (...) normal limb movements.Morton's hypothesis, thatlengthis controlled by a follow-up servo, has a number of difficulties related to the delays, gains, variability, and specificity in feedback pathways comprising potential servo loops. However, experimental evidence is consistent with these pathways providing servo assistance for some movements produced by coactivation of α- and static γ-motoneurons. Dynamic γ-motoneurons may provide an additional input for adaptive control of different types of movements.The idea that feedback is used to compensate for changes in musclestiffnesshas received experimental support under static postural conditions. However, reflexes tend to increase rather than decrease the range of variation in muscle stiffness during some cyclic movements. Theoretical problems associated with the regulation of stiffness are also discussed. The possibilities of separate control systems forvelocityorviscosityare considered, but the evidence is either negative or lacking. I conclude that different physical variables can be controlled depending on the type of limb movement required. The concept of stiffness regulation is also useful under some conditions, but should probably be extended to the regulation of the visco-elastic properties (i.e., the mechanical impedance) of a muscle or joint. (shrink)

Exclusively focused on data that are consistent with the proposed ideas, the target article misses an opportunity to review data that are inconsistent with them. Weaknesses of the emulation theory become especially evident when one tries to incorporate physiologically realistic muscle and reflex mechanisms into it. In particular, it fails to resolve the basic posture-movement controversy.

Prior to his renewed incumbency, as the fourth Prime Minister ofMalaysia, Mahathir Mohamad was able to remain in power for amore prolonged period compared to his predecessors. He was actively involvedin galvanizing political action immediately after the independence of Malaysiaand did not abandon active politics until his 2003 resignation. Under Mahathir’sleadership and guidance, Malaysia made remarkable economic and politicalprogress. He oversaw many innovations in the fledgling democracy and wasable to develop the country due to his exceptional leadership qualities. His styleand (...) attitude towards engaging with problems, particularly his stance during theAsian Monetary Crisis in 1997, was highly criticized by some, and labelled asdictatorial. This stigma did not detract him from the path he considered rightfor Malaysia, and under his leadership he garnered worldwide appreciation forhis national efforts and success in overcoming the economic crisis. Mahathiris undeniably an excellent case study as a prime minister, as well as a highly productive person. He contributed to a better understanding of modernMalaysia and his own tenure as PM in a series of books and articles. One ofthe significant aspects of his political heritage is his influential charisma andleadership. In all of his undertakings he has attracted both passionate supportand hatred from friends and foes, but his political footsteps have always beencertain and directed toward Malaysia’s national wellbeing. Mahathir is apolitician with sharp views on many issues and he was profoundly brave inverbalising them in the public arena, within Malaysia and internationally. Hisclear posture and speeches without fear made him a world-embracing politicalpersonality. This descriptive research study adopts a qualitative approach toanalyse historical information, documents, memoirs and articles, and books tobetter understand the leadership of Mahathir. (shrink)

ObjectivesTo investigate the effect of combined balance and plyometric training on knee function and proprioception of elite badminton athletes.MethodsSixteen elite male badminton players volunteered to participate and were randomly assigned to a combined balance and plyometric training and plyometric group. The CT group performed balance combined with plyometric training three times a week over 6 weeks ; while the PT group undertook only plyometric training for the same period. Both groups had the same technical training of badminton.ResultsThe knee function and (...) proprioception were assessed at baseline and after the intervention by measuring the performance of single-legged hop tests, standing postural sway, and LSI of dominant leg and non-dominant leg. The results showed that as compared to PT, CT induced significantly greater improvements in LSIT and LSIS.ConclusionIn elite badminton players, intervention using CT holds great promise to augment the benefits for knee function compared to the intervention using PT only, and at the same time, with at least comparable benefits for proprioception. Future studies are needed to examine and confirm the results of this study. (shrink)

Haptic-based vibrotactile biofeedback (BF) is a promising technique to improve rehabilitation of balance in stroke patients. However, the extent to which BF training changes temporal structure of the center of pressure (CoP) trajectories remains unknown. This study aimed to investigate the effect of vibrotactile BF training on the temporal structure of CoP during quiet stance in chronic stroke patients using detrended fluctuation analysis (DFA). Nine chronic stroke patients (age; 81.56±44 months post-stroke) received a balance training regimen using a vibrotactile BF (...) system twice a week over four weeks. A Wii Balance board was used to record five 30 s trials of quiet stance pre- and post-training at 50 Hz. DFA revealed presence of two linear scaling regions in CoP indicating presence of fast- and slow-scale fluctuations. Averaged across all trials, fast-scale fluctuations showed persistent dynamics ( = 1.05 ±.08 for ML and  = 0.99 ±.17 for AP) and slow-scale fluctuations were anti-persistent ( = 0.35 ±.05 for ML and  = 0.32 ±.05 for AP). The slow-scale dynamics of ML CoP in stroke patients decreased from pre-training to post-BF training ( = 0.40 ±.13 vs. 0.31 ±.09). These results suggest that the vibrotactile BF training affects postural control strategy used by chronic stroke patients in the ML direction. Results of the DFA are further discussed in the context of balance training using vibrotactile BF and interpreted from the perspective of intermittent control of upright stance. (shrink)

A pianist’s movements are fundamental to music-making by producing the musical sounds and the expressive movements of the trunk and arms which communicate the music’s structural and emotional information making it valuable for this review to examine upper-body movement in the performance process in combination with the factors important in skill acquisition. The underpinning playing technique must be efficient with economic muscle use by using body segments according to their design and movement potential with the arm segments mechanically linked to (...) produce coordinated and fluent movement. Two physiologically and pianistically important actions proposed by early music scientists to deliver the keystroke involve dropping the hand from the shoulders towards the keys via a wave action with the joints activated sequentially, and forearm rotation to position the fingers for the keystroke, an action followed by the elbow/upper-arm rotating in the opposite direction. Both actions spare the forearm muscles by generating the energy needed in the larger shoulder muscles. The hand in the playing position has a curved palm through action of the metacarpal (knuckle) joints and curved fingers. Palm/finger posture controls sound quality from loud, high tempo sounds to a more mellow legato articulation, and to perform effectively the forearms should slope down towards the keyboard. The technique must be automatic through systematic practice which develops the motor skills for proficient playing, with practice duration tempered to reduce the risk of causing injury through overuse of the forearm muscles. Efficient movement patterns and strategic muscle relaxation which results in faster movement are realized only through extensive training. The constant movements of the head and trunk, and flowing arm movement with frequent hand lifts and rotational elbow movements, although generated in producing the playing technique, resonate with audience members who perceive them as expressive and thereby creating in them an empathic engagement with the music. It was proposed that music students be trained in the mechanical aspects of upper-body use in the playing technique, and practice strategies, with specialist pedagogy for children to develop motor skills for efficient playing, and training methods fostering an appreciation of the communicative aspects of music performance. (shrink)

Instrumented assessments of quiet-stance postural control typically involve recording and analyzing of body sway signal, most often the center of pressure movement. It has been recently suggested that transient characteristics of body sway may offer additional information regarding postural control. In this study, we explored the relationship between whole-trial estimates of body sway and corresponding transient behavior indexes, as well as the effects of leg preference. A total of 705 healthy young athletes performed 30 s single-leg (...) body sway trials for both legs. It was found that the transient characteristics of the body sway are in negligible or weak correlation with the corresponding variables, averaged across the whole trial. All CoP variables showed transient characteristics, reflected in statistically significant decrease or increase throughout the trial. The preferred leg showed smaller body sway; however, the effect sizes were very small. Moreover, differences between the legs were also noted in terms of transient characteristics of body sway. In particular, the preferred leg showed earlier reduction in anterior–posterior body sway and larger reduction in medial–lateral body sway. Further studies should focus on examining the clinical utility of indexes of transient behavior of body sway, for instance, their sensitivity to aging-related changes and risk of falling. (shrink)

The understanding of locomotion in neurological disorders requires technologies for quantitative gait analysis. Numerous modalities are available today to objectively capture spatiotemporal gait and postural control features. Nevertheless, many obstacles prevent the application of these technologies to their full potential in neurological research and especially clinical practice. These include the required expert knowledge, time for data collection, and missing standards for data analysis and reporting. Here, we provide a technological review of wearable and vision-based portable motion analysis tools (...) that emerged in the last decade with recent applications in neurological disorders such as Parkinson's disease and Multiple Sclerosis. The goal is to enable the reader to understand the available technologies with their individual strengths and limitations in order to make an informed decision for own investigations and clinical applications. We foresee that ongoing developments toward user-friendly automated devices will allow for closed-loop applications, long-term monitoring, and telemedical consulting in real-life environments. (shrink)

Postural instability marks a prevalent symptom of Parkinson’s disease. It often manifests in increased body sway, which is commonly assessed by tracking the Center of Pressure. Yet, in terms of postural control, the body’s Center of Mass, and not CoP is what is regulated in a gravitational field. The aim of this study was to explore the effect of early- to mid-stage PD on these measures of postural control in response to unpredictable visual perturbations. We (...) investigated three cohorts: 18 patients with early to mid-stage PD [Hoehn & Yahr stage ; 1.94 ± 0.70]; a group of 15 age-matched controls ; and a group of 12 young healthy adults. Participants stood on a force plate to track their CoP, while the movement of their entire body was recorded with a video-based motion tracking system to monitor their CoM. A moving room paradigm was applied through a head-mounted virtual reality headset. The stimulus consisted of a virtual tunnel that stretched in the anterior-posterior direction which either remained static or moved back and forth in an unpredictable fashion.We found differences in mean sway amplitude and mean velocities of CoP and CoM between the groups under both conditions, with higher MSA of CoP and CoM for PD and higher mean velocities of both variables for PD and ECT when compared with YCT. Visual perturbation increased mean CoP velocity in all groups but did not have effects on mean CoM velocity or MSA. While being significantly lower for the young adults, the net effect of visual perturbation on mean CoP velocity was similar between patients with PD and age-matched controls. There was no effect of the visual perturbation on mean CoM velocity for any of the groups.Our simultaneous assessment of CoP and CoM revealed that postural control is reflected differently in CoM and CoP. As the motion of CoM remained mostly unaffected, all groups successfully counteracted the perturbation and maintained their balance. Higher CoP velocity for PD and ECT revealed increased corrective motion needed to achieve this, which however was similar in both groups. Thus, our results suggest increased effort, expressed in CoP velocity, to be an effect of age rather than disease in earlier stages of PD. (shrink)