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Our study aimed to examine differences in postural sway variables between Parkinson’s disease (PD) patients with freezing of gait (FOG) and those without freezing of gait (NFOG), with a particular focus on their fall history. Eighty-one patients with PD participated in this study, including 32 fallers and 49 nonfallers. In the faller group, 21 patients were classified into the FOG group, while 11 patients were categorized into the NFOG group. Each patient underwent a 30 s static postural balance assessment while standing on a custom-developed force plate. The center of pressure (COP) data was filtered and analyzed to derive key COP-based outcome measures. Independent t-tests were conducted to compare the FOG and NFOG groups within both faller and nonfaller subgroups. Spearman’s rank correlation analysis was conducted to investigate the association between COP-based outcomes and Tinetti balance scores. In the nonfaller group, FOG patients exhibited significantly greater mean distance ($p<$ 0.05), particularly in the mediolateral direction ($p<$ 0.01), compared to NFOG patients. Anterior–posterior (AP) peak power was also significantly higher in the FOG group ($p<$ 0.05), along with a larger sway area ($p<$ 0.05). However, no significant differences were noted within the faller group ($p>$ 0.05). Notably, in the nonfaller NFOG group, most COP-based variables were significantly correlated with Tinetti balance scores ($r=-$0.463 – 0.535, $p<$ 0.05), with stronger correlations observed in the mediolateral direction. No significant correlations were found in other groups ($p>$ 0.05). These findings may help clinicians in better distinguish between patients with and without FOG, considering their fall history.

The purpose of the present study was to examine the effects of long-term Tai Chi practice on postural balance and H-reflex. Sixteen healthy volunteers, eight with three or more years of experience in Tai Chi training (Tai Chi Group-TCG), and eight with no experience in Tai Chi training (Control Group-CG) participated in the study. Postural sways were measured under four experimental conditions: (1) Standing still with eyes open (EO); (2) Standing still with eyes closed (EC); (3) Standing and turning head to left and right with eyes open (EOT); and (4) Standing and turning head to left and right with eyes closed (ECT). Paired reflex depression (PRD) of the soleus muscle was measured under two conditions: supine and standing. Less significant postural sway was observed in the TCG than in the CG under four conditions including EO, EC, EOT, and ECT (p < 0.01). The TCG demonstrated 14.1%, 30.6%, 33.3% and 22.7% less postural sway, respectively. Significant PRD change from a supine to standing position was observed between TCG and CG (p < 0.05). A significant correlation between PRD change (from supine to standing) and years of Tai Chi practice was observed (r = 0.80, p < 0.05). The findings of this study support the positive effects of Tai Chi exercise on balance control under different conditions. Long-term Tai Chi exercisers also demonstrated different reflex modulation from a supine to standing position, and long-term Tai Chi practice may lead to a change of PRD modulation as neuroadaptation.

During quiet standing, the human body continuously moves about an upright posture in an erratic fashion. Many researchers characterize postural fluctuations as a stochastic process while some others suggest chaotic dynamics for postural sway. In this study, first we examined these assumptions using principles of chaos theory in normal healthy and in patients with deteriorated postural control mechanisms. Next, we compared the ability of a nonlinear dynamics quantifier correlation dimension to that of a linear measure standard deviation to describe variability of healthy and deteriorated postural control mechanisms during quiet standing. Our findings did not provide convincing evidence for existence of low dimensional chaos within normal and abnormal sway dynamics but support the notion that postural fluctuations time series are distinguishable from these generated by a random process. The results indicated that although linear variability measures discriminated well between groups, they did not provide any information about the structure of postural fluctuations. Calculated correlation dimension as a complexity measure which describes spatio temporal organization of time series may be useful in this regard.

When standing quietly, the human body is continuously moving about an upright posture in an erratic fashion. Conventional posturographic analyses that ignore structure of postural steadiness time series do not fully characterize properties of sway dynamics. Recurrence quantification analysis is a technique that can extract the dynamics of postural fluctuations through several variables. In this study, standing-still-sway dynamics of intact and deteriorated postural control systems were investigated by recurrence quantification of stabilograms. The results indicated that both normal and changed postural fluctuations time series, despite erratic and irregular appearance, contain a hidden structure. Although the two components of postural sway originated from an integrated control system, they exhibit distinct dynamical patterns. More determinism, greater local stability, higher degrees of nonstationarity and more laminar states were observed in fore-aft movements. Our findings reveal that decay of postural control mechanism affects dynamical properties of postural control system (especially along mediolateral direction because of the type of impairment). Determinism, nonstationarity and rigidity of balance program as well as laminar states characteristics were increased due to deterioration of postural control system. These findings imply that these measures not only can be used as the pathologic measures to discriminate between group differences, but also provide new openings to understand the nature of postural sway.

Postural control is an important aspect of human locomotion and stance. When inputs to the Central Nervous System (CNS), consisting of the vestibular, somatosensory, and visual senses, degrade or become dysfunctional, the postural control is affected. Biofeedback has been established as a potential intervention method to assist individuals improve postural control, by augmenting or complementing signals to the CNS. This paper presents an approach to help achieve better postural control using vibrotactile biofeedback. Tests to monitor postural control, in eyes open and eyes closed states, on a wobble board were introduced to assess the viability of the designed system in providing accurate real-time biofeedback responses. Postural control was gauged by measuring the angular displacement of perturbations experienced. Perturbations along the anterior and posterior direction are used to determine the level of provided vibrotactile biofeedback. The feedback informs subjects the severity of perturbation and direction of imbalance. Significant improvement (p-value < 0.05) in postural control while on perturbed surface was detected when the designed biofeedback system was used. The wearable system was found to be effective in improving postural control of the subjects and can be expanded for rehabilitation, conditioning, and strengthening applications dealing with human postural control.

This study investigated the quantitative scaling properties of the center of pressure (COP) as well as the spatial-temporal properties of the COP to elucidate the postural control behavior of healthy elderly (HE) adults and adults with Parkinson’s disease (PD) during quiet standing. Eighteen adults with PD and eighteen HE adults participated in this study. The COP movements were recorded while participants stood on either a firm surface or on a foam pad with their eyes either opened or closed. The sway ranges in the anterior–posterior (AP) ($R_x)$ and medio-lateral (ML) ($R_y)$ directions, the total length of the trajectory ($L)$, sway area ($A)$, and scaling exponents ($\alpha )$ from detrended fluctuation analysis were computed from the measured COP data. All temporal variables of the COP in all conditions were found to be significantly larger in the PD group than in the HE group. Low scaling exponents obtained for the PD group showed this group possessed diminished postural control ability compared to the HE group. The PD group showed unpredictable open-loop control in both the AP and ML directions. This proprioceptive control became predictable and the time scale relations decreased as the postural challenges increased. The AP and ML closed-loop control of the PD group was more predictable than that of the HE group only when proprioception was distorted using intact visual input, and the visual and proprioceptive inputs were both intact.

In this paper, we present a novel methodology to obtain imitative and innovative postural movements in a humanoid based on human demonstrations in a different kinematic scale. We collected motion data from a group of human participants standing up from a chair. Modeling the human as an actuated 3-link kinematic chain, and by defining a multi-objective reward function of zero moment point and joint torques to represent the stability and effort, we computed reward profiles for each demonstration. Since individual reward profiles show variability across demonstrating trials, the underlying state transition probabilities were modeled using a Markov chain. Based on the argument that the reward profiles of the robot should show the same temporal structure of those of the human, we used differential evolution to compute a trajectory that fits all humanoid constraints and minimizes the difference between the robot reward profile and the predicted profile if the robot imitates the human. Therefore, robotic imitation involves developing a policy that results in a temporal reward structure, matching that of a group of human demonstrators across an array of demonstrations. Skill innovation was achieved by optimizing a signed reward error after imitation was achieved. Experimental results using the humanoid HOAP-3 are shown.