Preferred step frequency minimizes veering during natural human walking

LoCoMoTe - A Framework for Classification of Natural Locomotion in VR by Task, Technique and Modality

Virtual reality (VR) research has provided overviews of locomotion techniques, how they work, their strengths and overall user experience. Considerable research has investigated new methodologies, particularly machine learning to develop redirection algorithms. To best support the development of redirection algorithms through machine learning, we must understand how best to replicate human navigation and behaviour in VR, which can be supported by the accumulation of results produced through live-user experiments. However, it can be difficult to identify, select and compare relevant research without a pre-existing framework in an ever-growing research field. Therefore, this work aimed to facilitate the ongoing structuring and comparison of the VR-based natural walking literature by providing a standardised framework for researchers to utilise. We applied thematic analysis to study methodology descriptions from 140 VR-based papers that contained live-user experiments. From this analysis, we developed the LoCoMoTe framework with three themes: navigational decisions, technique implementation, and modalities. The LoCoMoTe framework provides a standardised approach to structuring and comparing experimental conditions. The framework should be continually updated to categorise and systematise knowledge and aid in identifying research gaps and discussions.

The role of the nucleus pulposus in intervertebral disc recovery: Towards improved specifications for nucleus replacement devices

Nucleus replacement devices (NRDs) have potential to treat degenerated or herniated intervertebral discs (IVDs). However, IVD height loss is a post-treatment complication. IVD height recovery involves the nucleus pulposus (NP), but the mechanism of this in response to physiological loads is not fully elucidated. This study aimed to characterise the non-linear recovery behaviour of the IVD in intact, post-nuclectomy, and post-NRD treatment states, under physiological loading. 36 bovine IVDs (12 intact, 12 post-nuclectomy, 12 post-treatment) underwent creep-recovery protocols simulating Sitting, Walking or Running, followed by 12 h of recovery. A rheological model decoupled the fluid-independent (elastic, fast) and fluid-dependent (slow) recovery phases. In post-nuclectomy and post-treatment groups, nuclectomy efficiency (ratio of NP removed to remaining NP) was quantified following post-test sectioning. Relative to intact, post-nuclectomy recovery significantly decreased in Sitting (-0.3 ± 0.4 mm, p < 0.05) and Walking (-0.6 ± 0.3 mm, p < 0.001) coupled with significant decreases to the slow response (p < 0.05). Post-nuclectomy, the fast and slow responses negatively correlated with nuclectomy efficiency (p < 0.05). In all protocols, the post-treatment group performed significantly worse in recovery (-0.5 ± 0.3 mm, p < 0.01) and the slow response (p < 0.05). Results suggest the NP mainly facilitates slow-phase recovery, linearly dependent on the amount of NP present. Failure of this NRD to recover is attributed to poor fluid imbibition. Additionally, unconfined NRD performance cannot be extrapolated to the in vitro response. This knowledge informs NRD design criteria to provide high osmotic pressure, and encourages testing standards to incorporate long-term recovery protocols.

Mechanical and contact characteristics of foam materials within wound dressings: Theoretical and practical considerations in treatment

In the treatment of acute and chronic wounds, the clinical performance of a given foam-based dressing, and, ultimately, the wound healing and cost of care outcomes are strongly influenced by the mechanical performance of the foam material/s within that dressing. Most aspects of the mechanical performance of foam materials, for example, their stiffness, frictional properties, conformability, swelling characteristics and durability, and the overall mechanical protection provided by a foam-based dressing to a wound strongly depend on the microstructure of the foam components, particularly on their microtopography, density and porosity. This article, therefore, provides, for the first time, a comprehensive, self-inclusive compilation of clinically relevant theoretical and practical considerations, based on published analytical and experimental research as well as clinical experience related to the mechanical performance of foams in foam-based wound dressings. The current bioengineering information is useful for establishing understanding of the importance of mechanical properties of foams in foam-based dressings among clinicians and researchers in industry and academia, and other potential stakeholders in the wound care field, for example, regulators and buyers. This information is also particularly important for the development of standardised test methods for the evaluation of foam-based wound dressings and resulting standard mechanical performance metrics for these dressings.

An in vitro comparison of three nucleus pulposus removal techniques for partial intervertebral disc replacement: An ultra-high resolution MRI study

Background

Nuclectomy, also known as nucleotomy, is a percutaneous surgical procedure performed to remove nucleus material from the center of the disc. Multiple techniques have been considered to perform a nuclectomy, however, the advantages and disadvantages of each are not well understood.

Aims

This in vitro biomechanical investigation on human cadaveric specimens aimed to quantitatively compare three nuclectomy techniques performed using an automated shaver, rongeurs, and laser.

Material & Methods

Comparisons were made in terms of mass, volume and location of material removal, changes in disc height, and stiffness. Fifteen vertebra-disc-vertebra lumbar specimens were acquired from six donors (40 ± 13 years) and split into three groups. Before and after nucleotomy axial mechanical tests were performed and T2-weighted 9.4T MRIs were acquired for each specimen.

Results

When using the automated shaver and rongeurs similar volumes of disc material were removed (2.51 ± 1.10% and 2.76 ± 1.39% of the total disc volume, respectively), while considerably less material was removed using the laser (0.12 ± 0.07%). Nuclectomy using the automated shaver and rongeurs significantly reduced the toe-region stiffness (p = 0.036), while the reduction in the linear region stiffness was significant only for the rongeurs group (p = 0.011). Post-nuclectomy, 60% of the rongeurs group specimens showed changes in the endplate profile while 40% from the laser group showed subchondral marrow changes.

Discussion

From the MRIs, homogeneous cavities were seen in the center of the disc when using the automated shaver. When using rongeurs, material was removed non-homogeneously both from the nucleus and annulus regions. Laser ablation formed small and localized cavities suggesting that the technique is not suitable to remove large volumes of material unless it is developed and optimized for this application.

Conclusion

The results demonstrate that both rongeurs and automated shavers can be used to remove large volumes of NP material but the reduced risk of collateral damage to surrounding tissues suggests that the automated shaver may be more suitable.

Spine biomechanical testing methodologies: The controversy of consensus vs scientific evidence

Biomechanical testing methodologies for the spine have developed over the past 50 years. During that time, there have been several paradigm shifts with respect to techniques. These techniques evolved by incorporating state-of-the-art engineering principles, in vivo measurements, anatomical structure-function relationships, and the scientific method. Multiple parametric studies have focused on the effects that the experimental technique has on outcomes. As a result, testing methodologies have evolved, but there are no standard testing protocols, which makes the comparison of findings between experiments difficult and conclusions about in vivo performance challenging. In 2019, the international spine research community was surveyed to determine the consensus on spine biomechanical testing and if the consensus opinion was consistent with the scientific evidence. More than 80 responses to the survey were received. The findings of this survey confirmed that while some methods have been commonly adopted, not all are consistent with the scientific evidence. This review summarizes the scientific literature, the current consensus, and the authors' recommendations on best practices based on the compendium of available evidence.

Hidden Markov models identify major movement modes in accelerometer and magnetometer data from four albatross species

BACKGROUND

Inertial measurement units (IMUs) with high-resolution sensors such as accelerometers are now used extensively to study fine-scale behavior in a wide range of marine and terrestrial animals. Robust and practical methods are required for the computationally-demanding analysis of the resulting large datasets, particularly for automating classification routines that construct behavioral time series and time-activity budgets. Magnetometers are used increasingly to study behavior, but it is not clear how these sensors contribute to the accuracy of behavioral classification methods. Development of effective  classification methodology is key to understanding energetic and life-history implications of foraging and other behaviors.

METHODS

We deployed accelerometers and magnetometers on four species of free-ranging albatrosses and evaluated the ability of unsupervised hidden Markov models (HMMs) to identify three major modalities in their behavior: 'flapping flight', 'soaring flight', and 'on-water'. The relative contribution of each sensor to classification accuracy was measured by comparing HMM-inferred states with expert classifications identified from stereotypic patterns observed in sensor data.

RESULTS

HMMs provided a flexible and easily interpretable means of classifying behavior from sensor data. Model accuracy was high overall (92%), but varied across behavioral states (87.6, 93.1 and 91.7% for 'flapping flight', 'soaring flight' and 'on-water', respectively). Models built on accelerometer data alone were as accurate as those that also included magnetometer data; however, the latter were useful for investigating slow and periodic behaviors such as dynamic soaring at a fine scale.

CONCLUSIONS

The use of IMUs in behavioral studies produces large data sets, necessitating the development of computationally-efficient methods to automate behavioral classification in order to synthesize and interpret underlying patterns. HMMs provide an accessible and robust framework for analyzing complex IMU datasets and comparing behavioral variation among taxa across habitats, time and space.

Classifying sitting, standing, and walking using plantar force data

Prolonged static weight-bearing at work may increase the risk of developing plantar fasciitis (PF). However, to establish a causal relationship between weight-bearing and PF, a low-cost objective measure of workplace behaviors is needed. This proof-of-concept study assesses the classification accuracy and sensitivity of low-resolution plantar pressure measurements in distinguishing workplace postures. Plantar pressure was measured using an in-shoe measurement system in eight healthy participants while sitting, standing, and walking. Data was resampled to simulate on/off characteristics of 24 plantar force sensitive resistors. The top 10 sensors were evaluated using leave-one-out cross-validation with machine learning algorithms: support vector machines (SVMs), decision tree (DT), discriminant analysis (DA), and k-nearest neighbors (KNN). SVM and DT best classified sitting, standing, and walking. High classification accuracy was obtained with five sensors (98.6% and 99.1% accuracy, respectively) and even a single sensor (98.4% and 98.4%, respectively). The central forefoot and the medial and lateral midfoot were the most important classification sensor locations. On/off plantar pressure measurements in the midfoot and central forefoot can accurately classify workplace postures. These results provide the foundation for a low-cost objective tool to classify and quantify sedentary workplace postures.

Comparison of energy expenditure and substrate metabolism during overground and motorized treadmill running in Chinese middle-aged women

The purpose of this study was to compare differences of energy expenditure and substrate metabolism between motorized-treadmill and overground running in three different velocities in Chinese middle-aged women. In total, 74 healthy middle-aged women (age, 48 ± 4 years; height, 159.4 ± 4.9 cm; weight, 58.6 ± 6.7 kg; and body-mass index (BMI), 23.1 ± 2.7 kg/m²) volunteered to participate in this study. Bioelectrical-impedance analysis was used to measure body composition. Energy expenditure, carbohydrates (CHO), and fat oxidation were calculated with indirect calorimetry during motorized-treadmill and overground running. Running speed from slow to fast was 7.0, 8.0, and 9.0 km/h. The duration of each velocity was 6 min, separated by 5–15 min rest. There was no significant difference in energy expenditure between overground and treadmill running at the speed of 7 km/h (8.10 ± 1.25 vs. 7.75 ± 1.13 kcal/min, p > 0.05). Energy expenditure of overground running at 8 and 9 km/h was higher than that of treadmill running (9.36 ± 1.40 vs. 8.54 ± 1.21 kcal/min; 10.33 ± 1.55 vs. 9.54 ± 1.36 kcal/min; both p < 0.01). Fat contribution to energy consumption was significantly higher during treadmill running than during overground running (both p < 0.01) at speeds of 8 and 9 km/h. Overground running at high intensity incurred greater energy consumption than treadmill running did. However, results showed greater fat utilization during treadmill running than during overground running at high intensity. It is critical that these differences are taken into account when we prescribe training modes and intensities for middle-aged women.

Visual deprivation is met with active changes in ground reaction forces to minimize worsening balance and stability during walking

Previous studies suggest that visual information is essential for balance and stability of locomotion. We investigated whether visual deprivation is met with active reactions tending to minimize worsening balance and stability during walking in humans. We evaluated effects of vision on kinetic characteristics of walking on a treadmill-ground reaction forces (GRFs) and shifts in the center of mass (COM). Young adults (n = 10) walked on a treadmill at a comfortable speed. We measured three orthogonal components of GRFs and COM shifts during no-vision (NV) and full-vision (FV) conditions. We also computed the dynamic balance index (D_N)-the perpendicular distance from the projection of center of mass (pCOM) to the inter-foot line (IFL) normalized to half of the foot length. Locally weighted regression smoothing with alpha-adjusted serial T tests was used to compare GRFs and D_N between two conditions during the entire stance phase. Results showed significant differences in GRFs between FV and NV conditions in vertical and ML directions. Variability of peak forces of all three components of GRF increased in NV condition. We also observed significant increase in D_N for NV condition in eight out of ten subjects. The pCOM was kept within BOS during walking, in both conditions, suggesting that body stability was actively controlled by adjusting three components of GRFs during NV walking to minimize stability loss and preserve balance.

An Analysis Model Combining Gamma-Type Stirling Engine and Power Converter

Waste heat is a potential source for powering our living environment. It can be harvested and transformed into electricity. Ohmic heat is a common type of waste heat. However, waste heat has the following limitations: wide distribution, insufficient temperature difference (ΔT < 70 K) for triggering turbines, and producing voltage below the open voltage of the battery. This paper proposes an energy harvester model that combines a gamma-type Stirling engine and variable capacitance. The energy harvester model is different from Tavakolpour-Saleh’s free-piston-type engine [7.1 W at ΔT = 407 K (273–680 K)]. The gamma-type Stirling engine is a low-temperature-difference engine. It can be triggered by a minimum ΔT value of 12 K (293–305 K). The triggering force in the variable capacitance is almost zero. Furthermore, the gamma-type Stirling engine is suitable for harvesting waste heat at room temperature. This study indicates that 21 mW of energy can be produced at ΔT = 30 K (293–323 K) for a bias voltage of 70 V and volume of 103.25 cc. Because of the given bias voltage, the energy harvester can break through the open voltage of the battery to achieve energy storage at a low temperature difference.

Gait parameters are differently affected by concurrent smartphone-based activities with scaled levels of cognitive effort

The widespread and pervasive use of smartphones for sending messages, calling, and entertainment purposes, mainly among young adults, is often accompanied by the concurrent execution of other tasks. Recent studies have analyzed how texting, reading or calling while walking–in some specific conditions–might significantly influence gait parameters. The aim of this study is to examine the effect of different smartphone activities on walking, evaluating the variations of several gait parameters. 10 young healthy students (all smartphone proficient users) were instructed to text chat (with two different levels of cognitive load), call, surf on a social network or play with a math game while walking in a real-life outdoor setting. Each of these activities is characterized by a different cognitive load. Using an inertial measurement unit on the lower trunk, spatio-temporal gait parameters, together with regularity, symmetry and smoothness parameters, were extracted and grouped for comparison among normal walking and different dual task demands. An overall significant effect of task type on the aforementioned parameters group was observed. The alterations in gait parameters vary as a function of cognitive effort. In particular, stride frequency, step length and gait speed show a decrement, while step time increases as a function of cognitive effort. Smoothness, regularity and symmetry parameters are significantly altered for specific dual task conditions, mainly along the mediolateral direction. These results may lead to a better understanding of the possible risks related to walking and concurrent smartphone use.

Restricted vision increases sensorimotor cortex involvement in human walking

This study aimed to determine whether there is electrocortical evidence of augmented participation of sensory brain areas in walking modulation during walking with eyes closed. Healthy subjects (n = 10) walked on a treadmill at 1 m/s while alternating 5 min of walking with the eyes open or closed while we recorded ground reaction forces (GRFs) and high-density scalp electroencephalography (EEG). We applied independent component analysis to parse EEG signals into maximally independent component (IC) processes and then computed equivalent current dipoles for each IC. We clustered cortical source ICs and analyzed event-related spectral perturbations synchronized to gait events. Our results indicated that walking with eyes closed reduced the first peak of the vertical GRFs and induced shorter stride duration. Regarding the EEG, we found that walking with eyes closed induced significantly increased relative theta desynchronization in the frontal and premotor cortex during stance, as well as greater desynchronization from theta to beta bands during transition to single support for both left and right somatosensory cortex. These results suggest a phase-specific increased participation of brain areas dedicated to sensory processing and integration when vision is not available for locomotor guidance. Furthermore, the lack of vision demands higher neural processing related to motor planning and execution. Our findings provide evidence supporting the use of eyes-closed tasks in clinical practice, such as gait rehabilitation and improvements in balance control, as there is higher demand for additional sensory integration for achieving postural control.NEW & NOTEWORTHY We measured electrocortical dynamics in sighted individuals while walking with eyes open and eyes closed to induce the participation of other sensory systems in postural control. Our findings show that walking with visual restriction increases the participation of brain areas dedicated to sensory processing, motor planning, and execution. These results confirm the essential participation of supraspinal inputs to postural control in human locomotion, supporting the use of eyes-closed tasks in clinical practice.

Beaconing Signalization Substantially Reduces Blind Pedestrians' Veer on Snow-Covered Pavement

Veering outside of crosswalks is a common problem experienced by individuals who are blind. One technology found to be effective for reducing this veer when other guidance cues are absent is audible beaconing. However, veering in general and veering from crosswalks in particular have been studied primarily on smooth, flat walking surfaces such as clear pavement. This experiment compared veering on clear pavement with veering on snow-covered pavement, with and without audible beaconing. Eleven blind participants traveling with long canes attempted to walk a straight path for 72 ft (21.9 m), a typical length of a six-lane crosswalk. Beaconing substantially reduced veering at 36 ft (11.0 m) and 72 ft from the starting point and enabled participants to remain within a simulated crosswalk. Walking on snow was not found to affect veering but did increase the number of steps taken. The findings suggest that in snowy and clear conditions alike, audible beaconing is an effective wayfinding tool for intersections equipped with accessible pedestrian signals.

Walking in circles: a modelling approach

Blindfolded or disoriented people have the tendency to walk in circles rather than on a straight line even if they wanted to. Here, we use a minimalistic walking model to examine this phenomenon. The bipedal spring-loaded inverted pendulum exhibits asymptotically stable gaits with centre of mass (CoM) dynamics and ground reaction forces similar to human walking in the sagittal plane. We extend this model into three dimensions, and show that stable walking patterns persist if the leg is aligned with respect to the body (here: CoM velocity) instead of a world reference frame. Further, we demonstrate that asymmetric leg configurations, which are common in humans, will typically lead to walking in circles. The diameter of these circles depends strongly on parameter configuration, but is in line with empirical data from human walkers. Simulation results suggest that walking radius and especially direction of rotation are highly dependent on leg configuration and walking velocity, which explains inconsistent veering behaviour in repeated trials in human data. Finally, we discuss the relation between findings in the model and implications for human walking.