Natural Locomotion Research Articles

Numerical investigation of the forward and backward travelling waves through an undulating propulsor: performance and wake pattern

Recently, the mechanisms of natural undulatory locomotion of aquatic animal swimming have become one of the most significant issues for the researchers, swimmers and engineers. This study aims to elucidate and compare the propulsive vortical signature and performance of backward (negative undulation) and forward (positive undulation) travelling waves through a typical fishlike propulsor by a systematic numerical study. The numerical approach uses a pressure-based finite volume method solver to solve Navier–Stokes equations in an arbitrary Lagrangian–Eulerian framework domain containing a two-dimensional NACA 0012 foil moving with prescribed kinematics. Some of the important findings are: (1) time-dependent forces and pitching moments show that both mechanisms suffer from the energy losses; however, the negative undulations show less energy losses, (2) Strouhal number of undulations shows a transition point from drag-dominated regime to thrust-dominated regime for both mechanisms and a transition point from thrust-dominated regime to drag-dominated regime for positive undulation, (3) the consumed power plot shows that at lower and medium St, both mechanisms consume closely same powers, while, at higher St, the negative undulation consumes more power, (4) the efficiency plots show that the efficiency of the positive undulation is close to zero, while, the negative undulation reaches considerably higher performances, (5) low St vortical patterns of the mechanisms show some similarity, while, the patterns at medium and high St reveal appreciable discrepancies, and (6) the most significant difference between the vortical patterns of the mechanisms is appearing more regular and stronger vortices in the wake of the negative undulation.

Locomotion control of hybrid cockroach robots.

Natural systems retain significant advantages over engineered systems in many aspects, including size and versatility. In this research, we develop a hybrid robotic system using American (Periplaneta americana) and discoid (Blaberus discoidalis) cockroaches that uses the natural locomotion and robustness of the insect. A tethered control system was firstly characterized using American cockroaches, wherein implanted electrodes were used to apply an electrical stimulus to the prothoracic ganglia. Using this approach, larger discoid cockroaches were engineered into a remotely controlled hybrid robotic system. Locomotion control was achieved through electrical stimulation of the prothoracic ganglia, via a remotely operated backpack system and implanted electrodes. The backpack consisted of a microcontroller with integrated transceiver protocol, and a rechargeable battery. The hybrid discoid roach was able to walk, and turn in response to an electrical stimulus to its nervous system with high repeatability of 60%.

Influence of Lateral Dominance of Sight on the Quality of the Natural Locomotion Performance at the Senior Preschool Age

The article shows age-specific peculiarities of the formation of the asymmetry of visual perception and justifies the mechanisms of participation of the visual sensory system in the implementation of natural motor actions that contribute to the development of concepts of motor systems management, the development of the strategy of the typological approach to training and development of preschool children who demonstrate different types of lateral dominance. Experimental results were obtained using certified hardware. Recording of the surface EMG was performed using the “Neuro-Mvp” multipurpose computer system. Motor tasks under the control of binocular vision in the age of 5-6 years are implemented with the key role of the dominant eye. The narrowing of the visual field by means of closing the dominant eye during performance of a single manual action reduces the bioelectric activity of muscles due to the decrease in the maximum amplitude of the EMG signal, which indicates the reduction in the rate of muscles contraction. At the binocular method of sight, EMG of all studied muscle groups is characterized by the uniform bioelectric activity. When one is holding the “Flamingo” pose with closed eyes, disruption of the stability of the parameters of bioelectric activity takes place, which is manifested as appearing sharp bursts of the bioelectric activity in the EMG patterns. The sight space narrowing at closing the dominant eye leads to disruption of the bioelectric stability of postural muscles of the back and thigh. The sight space narrowing at closing the subdominant eye during holding the “Flamingo” pose leads to disruption of the bioelectric stability of postural muscles of the thigh.

Wide housing space and chronic exercise enhance physical fitness and adipose tissue morphology in rats.

The current cages commonly used in animal experiments can prevent rats from engaging in most forms of natural locomotion behaviors. These animals tend to exhibit sedentary habits. Here, we show that a combination of wide housing space and training exercise helps to reduce white adipose mass and to increase brown adipose mass. Thus, this combination is a useful strategy for truly enhancing the physical fitness of captive rats commonly used in exercise-related interventional studies and to maximize their welfare.

Wireless Neurosensor for Full-Spectrum Electrophysiology Recordings during Free Behavior

Brain recordings in large animal models and humans typically rely on a tethered connection, which has restricted the spectrum of accessible experimental and clinical applications. To overcome this limitation, we have engineered a compact, lightweight, high data rate wireless neurosensor capable of recording the full spectrum of electrophysiological signals fromthe cortex of mobile subjects. The wireless communication system exploits a spatially distributed network of synchronized receivers that is scalable to hundreds of channels and vast environments. To demonstrate the versatility of our wireless neurosensor, we monitored cortical neuron populations in freely behaving nonhuman primates during natural locomotion and sleep-wake transitions in ecologically equivalent settings. The interface is electrically safe and compatible with the majority of existing neural probes, which may support previously inaccessible experimental and clinical research.

Artificial tribotactic microscopic walkers: walking based on friction gradients.

Friction, the resistive force between two surfaces sliding past each other, is at the core of a wide diversity of locomotion schemes. While such schemes are well described for homogeneous environments, locomotion based on friction in inhomogeneous environments has not received much attention. Here we introduce and demonstrate the concept of tribotaxis, a motion that is guided by gradients in the friction coefficient. Our system is composed of microwalkers that undergo an effective frictional interaction with biological receptors on the substrate, which is regulated by the density of such receptors. When actuated stochastically, microwalkers migrate to regions of higher friction, much like a chemotactic cell migrates to regions of higher chemoattractant concentration. Simulations and theory based on biased random walks are in excellent agreement with experiments. We foresee important implications for tribotaxis in artificial and natural locomotion in biological environments.

Establishing the Range of Perceptually Natural Visual Walking Speeds for Virtual Walking-In-Place Locomotion

Walking-In-Place (WIP) techniques make it possible to facilitate relatively natural locomotion within immersive virtual environments that are larger than the physical interaction space. However, in order to facilitate natural walking experiences one needs to know how to map steps in place to virtual motion. This paper describes two within-subjects studies performed with the intention of establishing the range of perceptually natural walking speeds for WIP locomotion. In both studies, subjects performed a series of virtual walks while exposed to visual gains (optic flow multipliers) ranging from 1.0 to 3.0. Thus, the slowest speed was equal to an estimate of the subjects normal walking speed, while the highest speed was three times greater. The perceived naturalness of the visual speed was assessed using self-reports. The first study compared four different types of movement, namely, no leg movement, walking on a treadmill, and two forms of gestural input for WIP locomotion. The results suggest that WIP locomotion is accompanied by a perceptual distortion of the speed of optic flow. The second study was performed using a 4×2 factorial design and compared four different display field-of-views (FOVs) and two types of movement, walking on a treadmill and WIP locomotion. The results revealed significant main effects of both movement type and field of view, but no significant interaction between the two variables. Particularly, they suggest that the size of the display FOV is inversely proportional to the degree of underestimation of the virtual speeds for both treadmill-mediated virtual walking and WIP locomotion. Combined, the results constitute a first attempt at establishing a set of guidelines specifying what virtual walking speeds WIP gestures should produce in order to facilitate a natural walking experience.

Walking pace affected by interactive sounds simulating stepping on different terrains

This article investigates whether auditory feedback affects natural locomotion patterns. Individuals were provided with footstep sounds simulating different surface materials. The sounds were interactively generated using shoes with pressure sensors. Results showed that subjects' walking speed changed as a function of the type of simulated ground material. This effect may arise due to the presence of conflicting information between the auditory and foot-haptic modality, or because of an adjustment of locomotion to the physical properties evoked by the sounds simulating the ground materials. The results reported in this study suggest that auditory feedback may be more important in the regulation of walking in natural environments than has been acknowledged. Furthermore, auditory feedback could be used to develop novel approaches to the design of therapeutic and rehabilitation procedures for locomotion.

Whey Proteins Are More Efficient than Casein in the Recovery of Muscle Functional Properties following a Casting Induced Muscle Atrophy

The purpose of this study was to investigate the effect of whey supplementation, as compared to the standard casein diet, on the recovery of muscle functional properties after a casting-induced immobilization period. After an initial (I0) evaluation of the contractile properties of the plantarflexors (isometric torque-frequency relationship, concentric power-velocity relationship and a fatigability test), the ankle of 20 male adult rats was immobilized by casting for 8 days. During this period, rats were fed a standard diet with 13% of casein (CAS). After cast removal, rats received either the same diet or a diet with 13% of whey proteins (WHEY). A control group (n = 10), non-immobilized but pair-fed to the two other experimental groups, was also studied and fed with the CAS diet. During the recovery period, contractile properties were evaluated 7 (R7), 21 (R21) and 42 days (R42) after cast removal. The immobilization procedure induced a homogeneous depression of average isometric force at R7 (CAS: − 19.0±8.2%; WHEY: − 21.7±8.4%; P<0.001) and concentric power (CAS: − 26.8±16.4%, P<0.001; WHEY: − 13.5±21.8%, P<0.05) as compared to I0. Conversely, no significant alteration of fatigability was observed. At R21, isometric force had fully recovered in WHEY, especially for frequencies above 50 Hz, whereas it was still significantly depressed in CAS, where complete recovery occurred only at R42. Similarly, recovery of concentric power was faster at R21 in the 500−700°/s range in the WHEY group. These results suggest that recovery kinetics varied between diets, the diet with the whey proteins promoting a faster recovery of isometric force and concentric power output as compared to the casein diet. These effects were more specifically observed at force level and movement velocities that are relevant for functional abilities, and thus natural locomotion.

Horse-like walking, trotting, and galloping derived from kinematic Motion Primitives (kMPs) and their application to walk/trot transitions in a compliant quadruped robot

This manuscript proposes a method to directly transfer the features of horse walking, trotting, and galloping to a quadruped robot, with the aim of creating a much more natural (horse-like) locomotion profile. A principal component analysis on horse joint trajectories shows that walk, trot, and gallop can be described by a set of four kinematic Motion Primitives (kMPs). These kMPs are used to generate valid, stable gaits that are tested on a compliant quadruped robot. Tests on the effects of gait frequency scaling as follows: results indicate a speed optimal walking frequency around 3.4 Hz, and an optimal trotting frequency around 4 Hz. Following, a criterion to synthesize gait transitions is proposed, and the walk/trot transitions are successfully tested on the robot. The performance of the robot when the transitions are scaled in frequency is evaluated by means of roll and pitch angle phase plots.

How Do You Learn to Walk? Thousands of Steps and Dozens of Falls per Day

A century of research on the development of walking has examined periodic gait over a straight, uniform path. The current study provides the first corpus of natural infant locomotion derived from spontaneous activity during free play. Locomotor experience was immense: Twelve- to 19-month-olds averaged 2,368 steps and 17 falls per hour. Novice walkers traveled farther faster than expert crawlers, but had comparable fall rates, which suggests that increased efficiency without increased cost motivates expert crawlers to transition to walking. After walking onset, natural locomotion improved dramatically: Infants took more steps, traveled farther distances, and fell less. Walking was distributed in short bouts with variable paths—frequently too short or irregular to qualify as periodic gait. Nonetheless, measures of periodic gait and of natural locomotion were correlated, which indicates that better walkers spontaneously walk more and fall less. Immense amounts of time-distributed, variable practice constitute the natural practice regimen for learning to walk.

Model-Based Estimation of Knee Stiffness

During natural locomotion, the stiffness of the human knee is modulated continuously and subconsciously according to the demands of activity and terrain. Given modern actuator technology, powered transfemoral prostheses could theoretically provide a similar degree of sophistication and function. However, experimentally quantifying knee stiffness modulation during natural gait is challenging. Alternatively, joint stiffness could be estimated in a less disruptive manner using electromyography (EMG) combined with kinetic and kinematic measurements to estimate muscle force, together with models that relate muscle force to stiffness. Here we present the first step in that process, where we develop such an approach and evaluate it in isometric conditions, where experimental measurements are more feasible. Our EMG-guided modeling approach allows us to consider conditions with antagonistic muscle activation, a phenomenon commonly observed in physiological gait. Our validation shows that model-based estimates of knee joint stiffness coincide well with experimental data obtained using conventional perturbation techniques. We conclude that knee stiffness can be accurately estimated in isometric conditions without applying perturbations, which presents an important step toward our ultimate goal of quantifying knee stiffness during gait.

Impossible Spaces: Maximizing Natural Walking in Virtual Environments with Self-Overlapping Architecture

Walking is only possible within immersive virtual environments that fit inside the boundaries of the user's physical workspace. To reduce the severity of the restrictions imposed by limited physical area, we introduce "impossible spaces," a new design mechanic for virtual environments that wish to maximize the size of the virtual environment that can be explored with natural locomotion. Such environments make use of self-overlapping architectural layouts, effectively compressing comparatively large interior environments into smaller physical areas. We conducted two formal user studies to explore the perception and experience of impossible spaces. In the first experiment, we showed that reasonably small virtual rooms may overlap by as much as 56% before users begin to detect that they are in an impossible space, and that the larger virtual rooms that expanded to maximally fill our available 9.14 m x 9.14 m workspace may overlap by up to 31%. Our results also demonstrate that users perceive distances to objects in adjacent overlapping rooms as if the overall space was uncompressed, even at overlap levels that were overtly noticeable. In our second experiment, we combined several well-known redirection techniques to string together a chain of impossible spaces in an expansive outdoor scene. We then conducted an exploratory analysis of users' verbal feedback during exploration, which indicated that impossible spaces provide an even more powerful illusion when users are naive to the manipulation.

Enabling techniques for in vitro studies on mammalian spinal locomotor mechanisms

The neonatal rodent spinal cord maintained in vitro is a powerful model system to understand the central properties of spinal circuits generating mammalian locomotion. We describe three enabling approaches that incorporate afferent input and attached hindlimbs. (i) Sacral dorsal column stimulation recruits and strengthens ongoing locomotor-like activity, and implementation of a closed positive-feedback paradigm is shown to support its stimulation as an untapped therapeutic site for locomotor modulation. (ii) The spinal cord hindlimbs-restrained preparation allows suction electrode electromyographic recordings from many muscles. Inducible complex motor patterns resemble natural locomotion, and insights into circuit organization are demonstrated during spontaneous motor burst 'deletions', or following sensory stimuli such as tail and paw pinch. (iii) The spinal cord hindlimbs-pendant preparation produces unrestrained hindlimb stepping. It incorporates mechanical limb perturbations, kinematic analyses, ground reaction force monitoring, and the use of treadmills to study spinal circuit operation with movement-related patterns of sensory feedback while providing for stable whole-cell recordings from spinal neurons. Such techniques promise to provide important additional insights into locomotor circuit organization.

Optimal locomotion trajectory for biped robot ‘D2’ with knees stretched, heel-contact landings, and toe-off liftoffs

Most of the current biped robots with active revolute joints walk with their knees bent while a human walks without bending his or her knees in “natural” gaits. This paper proposes a method to generate natural locomotion trajectory for biped robots without bending knees based on a 2-DOF model of an inverted pendulum. In addition to the natural leg motion, this paper proposes a foot trajectory that has heel-contact landing and toe-off liftoff phases similar to the human foot. The trajectory is parameterized and optimized with a genetic algorithm based on energy consumption. In simulation of locomotion of biped robot, D2, which has a double deck structure of parallel mechanisms, the resulting trajectory looks natural and requires approximately 28% less energy than the one generated by the LIPM method. In addition to proposing the method to generate trajectory for a biped robot, this paper introduces the mechanism of serially linked parallel-mechanism for a biped robot with knees.

Natural Locomotion Interfaces – With a Little Bit of Magic!

The mission of the Immersive Media Group (IMG) is to develop virtual locomotion user interfaces which allow humans to experience arbitrary 3D environments by means of the natural walking metaphor. Traveling through immersive virtual environments (IVEs) by means of real walking is an important activity to increase naturalness of virtual reality (VR)-based interaction. However, the size of the virtual world often differs from the size of the tracked lab space so that a straightforward implementation of omni-directional and unlimited walking is not possible. Redirected walking is one concept to address this issue by inconspicuously guiding the user on a physical path that may differ from the path the user perceives in the virtual world. For example, intentionally rotating the virtual camera to one side causes the user to unknowingly compensate by walking on a circular arc into the opposite direction. In the scope of the LOCUI project, which is funded by the German Research Foundation, we analyze how gains of locomotor speed, turns and curvatures can gradually alter the physical trajectory with respect to the path perceived in the virtual world without the users observing any discrepancy. Thus, users can be guided in order to avoid collisions with physical obstacles (e.g., lab walls) or they can be guided to arbitrary locations in the physical space. For example, if the user approaches a virtual object, she can be guided to a real proxy prop that is registered to and aligned with its virtual counterpart. Hence, the user can interact with a virtual object by touching the corresponding real-world proxy prop that provides haptic feedback. Based on the results of psychophysical experiments we plan With such a user interface it becomes possible to intuitively interact with any virtual object by touching registered real-world props.

Effects of gait pattern and arm swing on intergirdle coordination

Mature locomotion in humans is characterized by an anti-phase coordination (moving in opposite directions) between the pelvic and the scapular girdles. This pattern involves a specific relationship between the arm and leg motion is deemed to be most flexible and dynamically efficient. Still, when the arms are involved in another task, like a field player running with a ball in the hands, locomotion is still possible. In order to probe the flexibility of the locomotor synergy, the present study aimed to determine the persistence and the strength of the coordination patterns between the pelvic and scapular girdles when no arm swing was allowed during walking and running.Relative phase, the time difference between the girdle rotations, measured the ongoing inter-girdle coordination of eight healthy participants asked to walk and run with or without arm swing. Results showed that an absence of arm swing led to a change from an anti-phase to in-phase pattern (girdles moving in the same direction) and that an increase in velocity strengthened the adopted pattern. Moreover, the frequency distribution of relative phase for all gait patterns with arm swing proved to be bimodal, indicating that the prevailing anti-phase pattern was always mixed with a noticeable proportion of in-phase coordination. The presence of the in-phase pattern in the easy, natural locomotion with arm swing manifests its persistence and its stability, perhaps pertaining to its prevalence in earlier times in ontogeny or evolution.

A Hybrid Class Underwater Vehicle: Bioinspired Propulsion, Embedded System, and Acoustic Communication and Localization System

AbstractInspired by the natural locomotion of jellyfish and squid, a series of compact thrusters series is developed for propulsion and maneuvering of underwater vehicles. These thrusters successively ingest and expel jets of water in a controlled manner at high frequencies to generate propulsive forces. The parameters controlling the performance of the thrusters are reviewed and investigated to achieve higher thrust levels. The thrusters are compact and can be placed completely inside a vehicle hull providing the desired maneuvering capability without sacrificing a sleek hydrodynamic shape for efficient cruising. The system design of a prototype hybrid vehicle, called CephaloBot, utilizing these thrusters, is also presented. A compact and custom-developed embedded system is also designed for the CephaloBot. Key features of the system include a base set of navigational sensors, an acoustic system for localization and underwater communication, Xbee RF transceiver for communication above water, and a LabVIEW programmed processing board.

Visually guided navigation: Head-mounted eye-tracking of natural locomotion in children and adults

The current study showed that visual fixation of obstacles is not required for rapid and adaptive navigation of obstacles. Children and adults wore a wireless, head-mounted eye-tracker during a visual search task in a room cluttered with obstacles. They spontaneously walked, jumped, and ran through the room, stepping up, down, and over obstacles. Both children and adults navigated adaptively without fixating obstacles, however, adults fixated less often than children. We discuss several possibilities for why obstacle navigation may shift from foveal to peripheral control over development.

The step space: example‐based footprint‐driven motion synthesis

AbstractEspecially in a constrained virtual environment, precise control of foot placement during character locomotion is crucial to avoid collisions and to ensure a natural locomotion. In this paper, we present the step space: a novel technique for generating animations of a character walking over a set of desired foot steps in real‐time. We use an efficient greedy nearest‐neighbor approach and warp the resulting animation such that it adheres to both spatial and temporal constraints. We use smart aligning and inverse kinematics to ensure spatial constraints and time warping for temporal constraints. We will show that our technique can generate realistic locomotion animations very efficiently even though we impose many constraints on the animation. Copyright © 2010 John Wiley &amp; Sons, Ltd.