Reactive postural responses to continuous yaw perturbations in healthy humans: the effect of aging

Maintaining balance stability while turning in a quasi-static stance and/or in dynamic motion requires proper recovery mechanisms to manage sudden center-of-mass displacement. Furthermore, falls during turning are among the main concerns of community-dwelling elderly population. This study investigates the effect of aging on reactive postural responses to continuous yaw perturbations on a cohort of 10 young adults (mean age 28 ± 3 years old) and 10 older adults (mean age 61 ± 4 years old). Subjects underwent external continuous yaw perturbations provided by the RotoBit1D platform. Different conditions of visual feedback (eyes opened and eyes closed) and perturbation intensity, i.e., sinusoidal rotations on the horizontal plane at different frequencies (0.2 Hz and 0.3 Hz), were applied. Kinematics of axial body segments was gathered using three inertial measurement units. In order to measure reactive postural responses, we measured body-absolute and joint absolute rotations, center-of-mass displacement, body sway, and inter-joint coordination. Older adults showed significant reduction in horizontal rotations of body segments and joints, as well as in center-of-mass displacement. Furthermore, older adults manifested a greater variability in reactive postural responses than younger adults. The abnormal reactive postural responses observed in older adults might contribute to the well-known age-related difficulty in dealing with balance control during turning

Microbiota-driven gut vascular barrier disruption is a prerequisite for non-alcoholic steatohepatitis development.

BACKGROUND & AIMS Fatty liver disease, including non-alcoholic fatty liver (NAFLD) and steatohepatitis (NASH), has been associated with increased intestinal barrier permeability and translocation of bacteria or bacterial products into the blood circulation. In this study, we aimed to unravel the role of both intestinal barrier integrity and microbiota in NAFLD/NASH development. METHODS C57BL/6J mice were fed with high-fat diet (HFD) or methionine-choline-deficient diet for 1 week or longer to recapitulate aspects of NASH (steatosis, inflammation, insulin resistance). Genetic and pharmacological strategies were then used to modulate intestinal barrier integrity. RESULTS We show that disruption of the intestinal epithelial barrier and gut vascular barrier (GVB) are early events in NASH pathogenesis. Mice fed HFD for only 1 week undergo a diet-induced dysbiosis that drives GVB damage and bacterial translocation into the liver. Fecal microbiota transplantation from HFD-fed mice into specific pathogen-free recipients induces GVB damage and epididymal adipose tissue enlargement. GVB disruption depends on interference with the WNT/β-catenin signaling pathway, as shown by genetic intervention driving β-catenin activation only in endothelial cells, preventing GVB disruption and NASH development. The bile acid analogue and farnesoid X receptor agonist obeticholic acid (OCA) drives β-catenin activation in endothelial cells. Accordingly, pharmacologic intervention with OCA protects against GVB disruption, both as a preventive and therapeutic agent. Importantly, we found upregulation of the GVB leakage marker in the colon of patients with NASH. CONCLUSIONS We have identified a new player in NASH development, the GVB, whose damage leads to bacteria or bacterial product translocation into the blood circulation. Treatment aimed at restoring β-catenin activation in endothelial cells, such as administration of OCA, protects against GVB damage and NASH development. LAY SUMMARY The incidence of fatty liver disease is reaching epidemic levels in the USA, with more than 30% of adults having NAFLD (non-alcoholic fatty liver disease), which can progress to more severe non-alcoholic steatohepatitis (NASH). Herein, we show that disruption of the intestinal epithelial barrier and gut vascular barrier are early events in the development of NASH. We show that the drug obeticholic acid protects against barrier disruption and thereby prevents the development of NASH, providing further evidence for its use in the prevention or treatment of NASH

Fifteen years of wireless sensors for balance assessment in neurological disorders

Balance impairment is a major mechanism behind falling along with environmental hazards. Under physiological conditions, ageing leads to a progressive decline in balance control per se. Moreover, various neurological disorders further increase the risk of falls by deteriorating specific nervous system functions contributing to balance. Over the last 15 years, significant advancements in technology have provided wearable solutions for balance evaluation and the management of postural instability in patients with neurological disorders. This narrative review aims to address the topic of balance and wireless sensors in several neurological disorders, including Alzheimer's disease, Parkinson's disease, multiple sclerosis, stroke, and other neurodegenerative and acute clinical syndromes. The review discusses the physiological and pathophysiological bases of balance in neurological disorders as well as the traditional and innovative instruments currently available for balance assessment. The technical and clinical perspectives of wearable technologies, as well as current challenges in the field of teleneurology, are also examined

Measuring biomechanical risk in lifting load tasks through wearable system and machine-learning approach

Ergonomics evaluation through measurements of biomechanical parameters in real time has a great potential in reducing non-fatal occupational injuries, such as work-related musculoskeletal disorders. Assuming a correct posture guarantees the avoidance of high stress on the back and on the lower extremities, while an incorrect posture increases spinal stress. Here, we propose a solution for the recognition of postural patterns through wearable sensors and machine-learning algorithms fed with kinematic data. Twenty-six healthy subjects equipped with eight wireless inertial measurement units (IMUs) performed manual material handling tasks, such as lifting and releasing small loads, with two postural patterns: correctly and incorrectly. Measurements of kinematic parameters, such as the range of motion of lower limb and lumbosacral joints, along with the displacement of the trunk with respect to the pelvis, were estimated from IMU measurements through a biomechanical model. Statistical differences were found for all kinematic parameters between the correct and the incorrect postures (p < 0.01). Moreover, with the weight increase of load in the lifting task, changes in hip and trunk kinematics were observed (p < 0.01). To automatically identify the two postures, a supervised machine-learning algorithm, a support vector machine, was trained, and an accuracy of 99.4% (specificity of 100%) was reached by using the measurements of all kinematic parameters as features. Meanwhile, an accuracy of 76.9% (specificity of 76.9%) was reached by using the measurements of kinematic parameters related to the trunk body segment

Estimation of Human Center of Mass Position through the Inertial Sensors-Based Methods in Postural Tasks: An Accuracy Evaluation

The estimation of the body’s center of mass (CoM) trajectory is typically obtained using force platforms, or optoelectronic systems (OS), bounding the assessment inside a laboratory setting. The use of magneto-inertial measurement units (MIMUs) allows for more ecological evaluations, and previous studies proposed methods based on either a single sensor or a sensors’ network. In this study, we compared the accuracy of two methods based on MIMUs. Body CoM was estimated during six postural tasks performed by 15 healthy subjects, using data collected by a single sensor on the pelvis (Strapdown Integration Method, SDI), and seven sensors on the pelvis and lower limbs (Biomechanical Model, BM). The accuracy of the two methods was compared in terms of RMSE and estimation of posturographic parameters, using an OS as reference. The RMSE of the SDI was lower in tasks with little or no oscillations, while the BM outperformed in tasks with greater CoM displacement. Moreover, higher correlation coefficients were obtained between the posturographic parameters obtained with the BM and the OS. Our findings showed that the estimation of CoM displacement based on MIMU was reasonably accurate, and the use of the inertial sensors network methods should be preferred to estimate the kinematic parameters

Artificial Neural Network for the Identification of Postural Instability in Subject Wearing Lower Limb Exoskeleton

Real-time processing of human response to external disturbances assumes a key role in the design of control systems for lower limb exoskeletons. However, the automatic recognition of human intention movement is still an untapped issue in robotics, especially when focusing on stability. In this study, we investigated the feasibility of using Artificial Neural Networks (ANN) to predict human postural response to perturbations in different directions. Fourteen healthy adults underwent standard baseline perturbations via a benchmarking system, B.E.A. T, while wearing the EXO-H2, a lower-extremity exoskeleton. Lower limb kinematics were measured using seven inertial sensors. The B.E.A.T. platform provided four perturbative scenarios with 8° tilt steps and tilt directions, following the four cardinal directions of north, east, south, and west. A set of5 ANNs with different kernels was tested to predict the four perturbative responses. Features extracted from lower limb joint angles were used to train and test the algorithms. The highest accuracy (95.3%) was obtained when applying the Narrow Neural Network. The lowest/highest values of true-positive/false-negative rates were found in the north direction. Our results provide relevant information to implement a similar algorithm in the control system of lower limb exoskeletons for instability management

Additive manufacturing structural redesign of hip prostheses for stress-shielding reduction and improved functionality and safety

Nowadays, the total hip arthroplasty (THA) is a widespread surgical procedure, representing the best option to restore hip joint mobility in patients suffering from trauma or joint diseases. One of the well-known possible drawbacks of THA is the stress-shielding phenomenon. Some years after the surgery, the femur starts to degrade because of its persistent unloaded condition induced by the high prosthesis stiffness, which carries the great part of the load normally taken by the bone. This condition is particularly invalidating in younger patients, with longer life expectation after the operation, requiring one or multiple additional operations to restore the proper prosthesis-bone firm connection. The present study tries to address this issue proposing an innovative prosthesis design, taking advantage of the shape freedom ensured by Additive Manufacturing techniques. Additionally, the structural integrity of the novel prosthesis is assessed using a ductile damage numerical approach. Different prosthesis geometries were investigated: one conventional and commercially available already, and two more innovative geometries. For each one, a bulk solution was compared to a lighter version characterized by an inner reticular structure with a body-centred cubic unit cell and by an equivalent density of about 5%, only feasible through the additive manufacturing fabrication. Extensive Finite Element numerical simulations were carried out to compare the percentage of the induced stress shielding for the different prosthesis geometries. Pros and cons of each geometry were pointed out and eventually the most promising solution in limiting the stress shielding phenomenon was chosen. At the same time, the structural integrity of the selected design was ensured, embedding a ductile damage model in the Finite Element analysis, calibrated on a SLM Ti6Al4V, the biocompatible alloy for the prosthesis fabrication. Structural safety was evaluated under four different loading conditions: walking, stumbling, the exceptional overload due to hammering insertion during surgery and the force which induced the collapse of the implant. Additionally, the safety margin was quantified through the definition of an overall safety factor under the maximum expected load

Muscle Activation Patterns Are More Constrained and Regular in Treadmill Than in Overground Human Locomotion

The use of motorized treadmills as convenient tools for the study of locomotion has been in vogue for many decades. However, despite the widespread presence of these devices in many scientific and clinical environments, a full consensus on their validity to faithfully substitute free overground locomotion is still missing. Specifically, little information is available on whether and how the neural control of movement is affected when humans walk and run on a treadmill as compared to overground. Here, we made use of linear and non-linear analysis tools to extract information from electromyographic recordings during walking and running overground, and on an instrumented treadmill. We extracted synergistic activation patterns from the muscles of the lower limb via non-negative matrix factorization. We then investigated how the motor modules (or time-invariant muscle weightings) were used in the two locomotion environments. Subsequently, we examined the timing of motor primitives (or time-dependent coefficients of muscle synergies) by calculating their duration, the time of main activation, and their Hurst exponent, a non-linear metric derived from fractal analysis. We found that motor modules were not influenced by the locomotion environment, while motor primitives were overall more regular in treadmill than in overground locomotion, with the main activity of the primitive for propulsion shifted earlier in time. Our results suggest that the spatial and sensory constraints imposed by the treadmill environment might have forced the central nervous system to adopt a different neural control strategy than that used for free overground locomotion, a data-driven indication that treadmills could induce perturbations to the neural control of locomotion.Peer Reviewe

Yaw Postural Perturbation Through Robotic Platform: Aging Effects on Muscle Synergies

Aging causes a worsening in muscle system, which could cause balance impairments, increasing the risk of falls. The study aims at evaluating the effects of aging on muscle activation in response to a yaw rotation imposed by the RotoBiT 1D . Eight younger and eight older adults were enrolled in the study. A right sigmoidal rotation of 55° around the yaw axis was imposed to the subject by means of the RotoBiT 1D platform in two velocity conditions, characterized by an angular velocity peak equal to 80¼/s and 100 °/s, respectively. The activations of 16 bilateral muscles of upper body were recorded through wireless surface electromyography. A Non-Negative Matrix Factorization was performed to extract the muscle synergies. The number of muscle synergies was selected by using the Variability Account For. The cosine of similarity was computed for the quantification of intra-group and inter-group similarity related to the muscle synergy vectors. The number of muscle synergies ranged from 4 to 6 in younger and from 3 to 6 in older, even though no statistical difference was found between groups or velocity conditions. As regards intra-group similarity, younger adults showed values always above the similarity threshold; while a lower similarity was observed in older adults, confirming the heterogeneity of postural response. The overall structure of muscle synergy vectors was not similar between groups and the inter-group similarity decreased with the increase of the velocity. The differences were greater in synergies involving head and upper limb muscles. Findings unveiled a different muscle synergy organization in terms of muscle synergy vectors. Such a different organization calls for a deeper investigation towards the aim of identifying causes of fall in elderly