Dynamic Walking Stability Research Articles

Effects of the kinematic variable, time delay and data length on test-retest reliability of the maximal Lyapunov exponent of human walking.

The maximal Lyapunov exponent (MLE) has been used to quantify the dynamic stability of human locomotion. The method for estimating MLE requires selecting a proper time series of kinematic variables and reconstructing phase space using proper time delay. The data length also affects the reliability of the measured MLE. However, there has been no criterion for the choice of the time series, time delay or data length. Here, we quantified the effect of these factors on the test-retest reliability of MLE estimations. We recruited 15 young and healthy adults and let them walk on a treadmill three times. We calculated MLE employing various lengths of time series of 18 frequently used kinematic variables and two typical choices of time delay: fixed delay and delay selected by average mutual information algorithm. Then, we measured the intraclass correlation coefficient (ICC) of the measured MLE under each condition. Our results show that the choice of time delay does not affect reliability. Five among the 18 kinematic variables enabled excellent reliability with ICC above 0.9 within 450 strides and also enabled ICC above 0.75 even with 60 or less strides. These findings can contribute to establishing the criteria for measuring the dynamic stability of human walking.

Dynamic Stability of Human Walking in Response to Sudden Speed Changes

Abrupt changes in gait speed can interfere with the symmetry of the overall gait apparatus and result in unstable joint movement patterns. Because unstable joint movements may cause slips, trips, and falls, it is necessary to quantitatively characterize the changes in joint movement patterns in response to sudden speed changes. The purpose of this study is to examine how abrupt changes in gait speed affect gait dynamics. Twenty-two healthy young subjects walked for four minutes, including a warm-up period, under three different speed conditions. Utilizing nonlinear dynamics tools, including the maximum Lyapunov exponent, Sample Entropy, and Detrended Fluctuation Analysis, we quantitatively assessed gait dynamics for the different speed conditions. Our findings highlight how different speed change patterns impact joint instability, notably within the knee joint during gait (p < 0.05). Furthermore, introducing a resting phase during random speed changes exhibited the potential to restore gait symmetry and control movement patterns. This research offers valuable insights into human gait stability dynamics, especially concerning sudden speed changes. Understanding how controlled speed variations affect gait and joint instability informs fall prevention and rehabilitation strategies, emphasizing speed management to improve gait symmetry and reduce joint instability.

Mediolateral foot placement control can be trained: Older adults learn to walk more stable, when ankle moments are constrained.

Falls are a problem, especially for older adults. Placing our feet accurately relative to the center-of-mass helps us to prevent falling during gait. The degree of foot placement control with respect to the center-of mass kinematic state is decreased in older as compared to young adults. Here, we attempted to train mediolateral foot placement control in healthy older adults. Ten older adults trained by walking on shoes with a narrow ridge underneath (LesSchuh), restricting mediolateral center-of-pressure shifts. As a training effect, we expected improved foot placement control during normal walking. A training session consisted of a normal walking condition, followed by a training condition on LesSchuh and finally an after-effect condition. Participants performed six of such training sessions, spread across three weeks. As a control, before the first training session, we included two similar sessions, but on normal shoes only. We evaluated whether a training effect was observed across sessions and weeks in a repeated-measures design. Whilst walking with LesSchuh, the magnitude of foot placement error reduced half-a-millimeter between sessions within a week (cohen's d = 0.394). As a training effect in normal walking, the magnitude of foot placement errors was significantly lower compared to the control week, by one millimeter in weeks 2 (cohen's d = 0.686) and 3 (cohen's d = 0.780) and by two millimeters in week 4 (cohen's d = 0.875). Local dynamic stability of normal walking also improved significantly. More precise foot placement may thus have led to improved stability. It remains to be determined whether the training effects were the result of walking on LesSchuh or from repeated treadmill walking itself. Moreover, enhancement of mechanisms beyond the scope of our outcome measures may have improved stability. At the retention test, gait stability returned to similar levels as in the control week. Yet, a reduction in foot placement error persisted.

Dynamic Stability of Passive Dynamic Walking Following Unexpected Perturbations.

Mitigating the risk of falling is an area of significant interest among clinicians due to the often profound health-related consequences of falls. Consequently, there is acute interest in characterizing the biomechanical conditions associated with increased fall risk, and in methods for quantifying gait stability under those conditions toward predicting and ultimately preventing falls. Considerable insights into the biomechanics of fall risk have been provided by examining the passive dynamic walking (PDW) model under nominal and perturbed conditions. This work aims to expand upon prior efforts and develop the PDW model as a model of tripping and slipping by simulating and analyzing the behavior of the model during transient perturbations. We show that fall risk increases with increasing perturbation magnitude, yet stable walking may be found even with fairly large perturbations. In cases where transient perturbations result in a fall, a nontrivial portion exhibit a substantial period of stumbling before the fall, indicating an opportunity for developing early fall-risk detection and intervention techniques. In such cases, we show that widely used kinematic metrics are able to predict whether or not a fall will occur with up to 82% balanced accuracy, even when a variety of gait kinematics are considered.

Abstract TP64: Determining The Role Of Single Support Center Of Pressure Distance For Characterizing Post-stroke Walking Impairment And Response To Rehabilitation Training

Introduction: Stroke is a major cause of balance and walking impairment and is on the rise. The most widely used walking impairment measure is the 10-meter walk test (10-mWT), which provides information about walking speed but does not inform about walking kinematics or neuromuscular control. Objective: Herein, we evaluate single support center of pressure distance (SS CoP Dist), a kinematic measure of dynamic postural control and walking stability, as a complementary measure of walking impairment. We hypothesize that SS CoP Dist will be closely associated with baseline walking speed, and will improve with Backward Locomotor Treadmill Training (BLTT). Methods: Thirty-six chronic stroke survivors with residual walking impairment, based on 10-mWT speed [ mild >0.8 m/s (n =7); moderate 0.4-0.8m/s (n =18); and severe <0.4 m/s (n = 11)] , underwent six 30-minute BLTT sessions over two consecutive weeks. During testing (10-mWT), participants were instructed to walk as fast as possible over the gait analysis mat to capture SS CoP Dist and walking speed. Results: At baseline, there was a weak to moderate positive relationship between walking speed and SS CoP Dist (R 2 paretic = 0.22, p = 0.0036; R 2 Nonparetic = 0.44, p < 0.0001). Following BLTT, SS COP Dist increased (more stable) in the mild and moderate groups [mild paretic ( p = 0.0039)/mild Nonparetic ( p = 0.0034) , moderate paretic ( p = 0.0360)/ moderate Nonparetic ( p = 0.0087)], with improved interlimb symmetry in the mild group. In contrast, no significant improvement in SS CoP Dist was seen in participants with severe walking impairment ( p = 0.3830). Training-related changes in walking speed were strongly correlated with change in SS CoP Dist (R 2 Nonparetic = 0.54, p = 0.0007). Conclusion: Our preliminary findings suggest that SS CoP Dist compliments walking speed for characterizing walking severity and response to training in chronic stroke survivors. In addition, BLTT significantly improved SS CoP Dist in mild-moderately impaired stroke survivors but not in survivors with severe walking impairment. Future well-powered, prospective studies with BLTT and other training paradigms are needed to validate these findings.

An Exploration Into Potential Contributing Factors to Upper Limb Associated Reactions in People With Acquired Brain Injury

<h3>Research Objectives</h3> To determine which potential contributing factors are associated with upper limb associated reaction (AR) expression in individuals with acquired brain injury (ABI). <h3>Design</h3> Cross-sectional observational study. <h3>Setting</h3> A major brain injury rehabilitation centre in Australia. <h3>Participants</h3> Forty-two participants with an adult-onset, non-progressive ABI and an AR in their hemiplegic upper limb during walking were recruited. <h3>Interventions</h3> N/A <h3>Main Outcome Measures</h3> Participants underwent three-dimensional motion analysis at self-selected walking speed to generate an AR outcome measure, quantifying upper limb kinematic deviation compared to healthy controls. Clinical assessment of potential contributing factors included: upper and lower limb hypertonicity, spasticity and strength, balance, dynamic walking stability, arm and leg function, anxiety, arm pain/discomfort, and fear of falling. <h3>Results</h3> Significant, moderate-to-strong correlations (r = 0.42 - 0.74, p < 0.05) existed between upper limb ARs and both hypertonicity and spasticity of the upper limb muscles and the knee extensors. Significant, moderate correlations to ARs (r = 0.42 - 0.59, p < 0.05) existed for balance, dynamic stability, upper limb strength, and arm function. Those participants who had hypertonicity of shoulder internal rotators, elbow, forearm, and finger flexors; spasticity of the elbow and finger flexors; knee extensor spasticity; and, reduced dynamic stability had a more severe AR (p < 0.05; effect sizes ≥ 0.80). Associated reactions were however present in the absence of positive upper motor neuron syndrome features. For example, 21% of participants had an elbow joint axis AR without elbow flexor hypertonicity and 33% without elbow flexor spasticity. <h3>Conclusions</h3> Associated reactions are complex and multi-factorial. There were several significant correlations and factors that may influence AR severity. While positive upper motor neuron syndrome features should be prioritised for clinical assessment, these factors are not prerequisites for ARs. <h3>Author(s) Disclosures</h3> There are no disclosures or conflicts to declare.

Two-dimensional dynamic walking stability of elderly females with a history of falls.

Injuries related with falls are a major health risk for the elderly. Accurate evaluation of the dynamic walking stability of elderly people is the key to fall prevention. A two-dimensional (2-D) model is proposed in this study given that the custom method is mainly focused on the dynamic walking stability along the antero-posterior axis. An inverted pendulum model was utilised to calculate the region of stability at toe-off, and stability conditions were evaluated first along the antero-posterior and medio-lateral axes. The analysis was then extended to the 2-D plane. In the 2-D case, the region of stability was determined based on the use of the information of the envelope of the foot. Twenty-four female participants, categorised as healthy young, healthy elderly, and elderly with a history of falls, were examined. Significant differences among the three groups were demonstrated with the 2-D analysis method, but not in the antero-posterior or medio-lateral analyses. The centre-of-masses of elderly fallers were significantly closer to the foot-supporting boundary compared with that of healthy young and elderly adults at toe-off. A 2-D analysis method using the envelope-of-foot could evaluate the dynamic stability of elderly females based on a more accurate scale.

Potential contributing factors to upper limb associated reactions in people with acquired brain injury: an exploratory study

Purpose To determine which potential contributing factors are associated with upper limb associated reaction (AR) expression in individuals with acquired brain injury (ABI). Methods Forty-two participants underwent three-dimensional motion analysis at self-selected walking speed to generate the AR outcome measure, quantifying their upper limb kinematic deviation compared to healthy controls. Clinical assessment included: upper and lower limb hypertonicity, spasticity and strength, balance, dynamic walking stability, arm and leg function, anxiety, arm pain/discomfort, and fear of falling. Results Significant, moderate-to-strong correlations (r = 0.42–0.74, p < 0.05) existed between upper limb ARs and both hypertonicity and spasticity of the upper limb muscles and the knee extensors. Significant, moderate correlations to ARs (r = 0.42–0.59, p < 0.05) existed for balance, dynamic stability, upper limb strength, and arm function. The severity of AR was significantly different between those with and without hypertonicity of the four tested upper limb muscles, elbow and long finger flexor spasticity, knee extensor spasticity, and reduced dynamic stability (p < 0.05; effect sizes ≥0.80). However, these contributing factors were not present in all participants. Conclusions Associated reactions are complex and multi-factorial. There were several significant correlations indicating that factors may influence AR severity. While positive upper motor neuron syndrome features should be prioritised for clinical assessment, these factors are not prerequisites for ARs. IMPLICATIONS FOR REHABILITATION Upper limb associated reactions are a complex and multi-factorial phenomenon. Upper limb muscle hypertonicity and spasticity should be prioritised for assessment; however, they are not prerequisites for associated reactions. Hypertonicity and spasticity should be differentiated as they may have differing relationships to associated reactions. Knee extensor hypertonicity and spasticity, postural stability, upper limb strength, and arm function may also be contributing factors to consider.

Fuzziness of muscle synergies in patients with multiple sclerosis indicates increased robustness of motor control during walking

Deficits during gait poses a significant threat to the quality of life in patients with Multiple Sclerosis (MS). Using the muscle synergy concept, we investigated the modular organization of the neuromuscular control during walking in MS patients compared to healthy participants (HP). We hypothesized a widening and increased fuzziness of motor primitives (e.g. increased overlap intervals) in MS patients compared to HP allowing the motor system to increase robustness during walking. We analysed temporal gait parameters, local dynamic stability and muscle synergies from myoelectric signals of 13 ipsilateral leg muscles using non-negative matrix factorization. Compared to HP, MS patients showed a significant decrease in the local dynamic stability of walking during both, preferred and fixed (0.7 m/s) speed. MS patients demonstrated changes in time-dependent activation patterns (motor primitives) and alterations of the relative muscle contribution to the specific synergies (motor modules). We specifically found a widening in three out of four motor primitives during preferred speed and in two out of four during fixed speed in MS patients compared to HP. The widening increased the fuzziness of motor control in MS patients, which allows the motor system to increase its robustness when coping with pathology-related motor deficits during walking.

Investigation on the effect of noisy galvanic vestibular stimulation on fine motor skills during a visuomotor task in healthy participants.

Noisy galvanic vestibular stimulation (nGVS) has been shown to improve dynamic walking stability, affect postural responses, enhance balance in healthy subjects, and influence motor performance in individuals with Parkinson’s disease. Although the studies to fully characterize the effect of nGVS are still ongoing, stochastic resonance theory which states that the addition of noisy signal may enhance a weak sensory input signals transmission in a non-linear system may provide a possible explanation for the observed positive effects of nGVS. This study explores the effect of nGVS on fine tracking behavior in healthy subjects. Ten healthy participants performed a computer-based visuomotor task by controlling an object with a joystick to follow an amplitude-modulated signal path while simultaneously receiving a sham or pink noise nGVS. The stimulation was generated to have a zero-mean, linearly detrended 1/f-type power spectrum, Gaussian distribution within 0.1–10 Hz range, and a standard deviation (SD) set to 90% based on each participant’s cutaneous threshold value. Results show that simultaneous nGVS delivery statistically improved the tracking performance with a decreased root-mean-squared error of 5.71±6.20% (mean±SD), a decreased time delay of 11.88±9.66% (mean±SD), and an increased signal-to-noise ratio of 2.93% (median, interquartile range (IQR) 3.31%). This study showed evidence that nGVS may be beneficial in improving sensorimotor performance during a fine motor tracking task requiring fine wrist movement in healthy subjects. Further research with a more comprehensive subset of tasks is required to fully characterize the effects of nGVS on fine motor skills.

A Multi-module Controller for Walking Quadruped Robots

Motion control based on biologically inspired methods, such as Central Pattern Generator (CPG) models, offers a promising technique for robot control. However, for a quadruped robot which needs to maintain balance while performing flexible movements, this technique often requires a complicated nonlinear oscillator to build a controller, and it is difficult to achieve agility by merely modifying the predefined limit cycle in real time. In this study, we tried to solve this problem by constructing a multi-module controller based on CPG. The different parallel modules will ensure the dynamic stability and agility of walking. In the proposed controller, a specific control task is accomplished by adding basic and superposed motions. The basic motions decide the basic foot end trajectories, which are generated by the predefined limit cycle of the CPG model. According to conventional kinematics-based design, the superposed motions are generated through different modules alter the basic foot end trajectories to maintain balance and increase agility. As a considerable stability margin can be achieved, different modules are designed separately. The proposed CPG-based controller is capable of stabilizing a walking quadruped robot and performing start and stop movements, turning, lateral movement and reversal in real time. Experiments and simulations demonstrate the effectiveness of the method.

Hybrid CPG–FRI dynamic walking algorithm balancing agility and stability control of biped robot

Dynamic walking fulfill agility and stability simultaneously is one of the most difficulty for biped robot control. The traditional zero moment point (ZMP) is the most commonly used reference point for biped robot static and quasi dynamic walking control. However, human walking experimental results indicate that during walking process of human beings, the ZMP trajectory is not always conformed to the requirement of stability, such as giant strides, acceleration walking or fast walking. In order to reveal the mechanism of the biped dynamic walking, this paper proposed a novel stability criterion for the biped walking by tuning the conventional fixed support polygon area to an adjustable one. This method includes the tiptoe underactuated phase of the support foot during the biped walking. A new algorithm for the real-time biped walking generation by combining central pattern generation (CPG) with foot rotation indicator (FRI) is presented. The FRI monitor establishes the mapping function between the center of mass of the biped robot with the boundary of the elastic support polygon. By introducing FRI information, the CPG parameters can be adjusted in real time to generate a rhythmic and stable walking pattern. Numerical simulation results show that the proposed algorithm extends the application area of the ZMP criterion and improves the walking velocity of the biped robot. Moreover, the algorithm builds a bridge for the dynamic biped walking from the robot agility to motor parameters. This means that the agility of the biped robot can be quantitative controlled by modulating the motor parameters.

On the manipulability of swing foot and stability of human locomotion

Manipulability is a measure that quantifies the range of possible motions of a robotic end-effector and it is also an important measure in the study of coordination of human upper body and grasping tasks. This measure, which is defined on both the kinematic and dynamic level, could be useful in gait, as it could be used to determine potential foot placement possibilities. Kinematic manipulability is defined based on the Jacobian and dynamic manipulability on both the Jacobian and mass-inertia matrix. The main purpose of this study was to evaluate the manipulability of human walking and to explore a possible relation between the manipulability and dynamic stability of walking at different speeds. A 37-DoF tree-like model of the human body was developed to evaluate the manipulability index of human walking. We measured kinematics of 11 healthy male subjects while walking on a treadmill, and mapped the data to the model using inverse kinematics. Jacobian based kinematic/dynamic manipulability measures of walking were evaluated for the swing phase of walking. Manipulability ellipsoids were drawn for geometric determination of this measure in all directions during early, mid- and late swing phases. As stability metrics, the local divergence exponent and Floquet Multipliers were calculated. The results indicated a high kinematic manipulability of the swing foot during early and late swing phases and a drop in kinematic manipulability during mid-swing. Kinematic manipulability of the swing leg during early and late (but not mid-) swing phases increased with walking speed but the average kinematic manipulability of the center of mass and dynamic manipulability of swing foot decreased with increasing walking speed. Moreover, the results showed a weak relation between the manipulability and local and orbital stability.

Dynamic walking stability of elderly people with various BMIs

BackgroundFalls are one of the major causes of injury in the elderly. Obesity may be related to the risk of falling. Understanding the dynamic stability mechanisms of obese elderly people during gait is important as it may be associated with fall protection. Research questionDoes obesity affect the dynamic walking stability of elderly people? MethodsThis is a prospective study. Fifty-three elderly participants, aged 60–82 years, were categorized into body mass index (BMI) groups. In single-limb support experiments, the center of mass velocity (COMv), center of mass acceleration (COMa), region of velocity stability (ROSv) and region of acceleration stability (ROSa) were calculated using kinematic data sampled from a motion analysis system. In addition, all participants were assessed for the dynamic balance ability test scale (DBATS). Statistical analyses were performed by one-way ANOVA, Kruskal–Wallis/Wilcoxon nonparametric tests, or bivariate Pearson/Spearman correlation analysis. ResultsDuring walking, peak COMv and COMa decreased with increasing BMI (Normal BMI: 1.20 ± 0.14 m/s, 1.66 ± 0.36 m/s2; High BMI: 1.14 ± 0.11 m/s, 1.56 ± 0.30 m/s2; Higher BMI: 1.04 ± 0.15 m/s, 1.47 ± 0.25 m/s2). At toe-off (TO), the normalized participants’ center of mass (COM) is significantly more anterior in the Higher BMI group (Normal BMI: -0.30 ± 0.09, High BMI: -0.23 ± 0.07, Higher BMI: -0.16 ± 0.10), their normalized COMv and COMa (Normal BMI: 1.40 ± 0.16, 0.53 ± 0.11; High BMI: 1.33 ± 0.13, 0.49 ± 0.11; Higher BMI: 1.21 ± 0.16, 0.46 ± 0.11) are slower. The mean DBATS score of the Higher BMI group was the highest, indicating the weakest dynamic balance ability. SignificanceThe COM dynamic stability parameters indicate that obesity may worsen balance, with the peak COMv and ROSv most affected. With increasing BMI, the dynamic stability and balance of elderly people both decreased.

Effects of physical exhaustion on local dynamic stability and automaticity of walking

BackgroundWhile the effects of diseases, performance of proprioceptors, anxiety or pain on gait stability or automaticity of walking are well-explored, physical fatigue might be another relevant factor whose consequences are not sufficiently investigated, yet. Research questionThe aim of the current study was to evaluate the effect of physical exhaustion on local dynamic stability (LDS) and automaticity of gait. MethodsIn a randomized controlled trial, 30 young and healthy adults were randomly assigned to either a passive control group or a fatigue group. The participants assigned to the fatigue group passed a shuttle-run test which finished at maximal exhaustion while those of the control group rested in sitting position for 15 min. Immediately before and after the intervention, local dynamic gait stability as well as the cognitive (serial seven subtractions) and motor dual-task costs, as a measure of automaticity, were registered. ResultsWhile there was no effect of fatigue on LDS during single-task walking, we observed an interaction effect for LDS in the dual-task condition (p = .034) and for the motor dual-task costs (p = .031). Lower dual-task costs were found in the fatigued group in the post-test compared to the pre-test while the control group increased their costs at the same time. SignificanceIn conclusion, gait automaticity might increase after total exhaustion in young adults. Still, the underlying mechanisms are not completely resolved and further research incorporating measurements of cortical gait control might be promising.

Stability improvement of a dynamic walking system via reversible switching surfaces

Inspired by the effects of a switching surface on the stability of passive dynamic walking (Safa and Naraghi in Robotica 33(01):195–207, 2015; Safa et al. in Nonlinear Dyn. 81(4):2127–2140, 2015), this paper suggests a new control strategy for stabilization of dynamic bipedal locomotion. It verifies that the stability improvement of a dynamic walking system is feasible while preserving the speed, step-length, period, natural dynamics, and the energy effectiveness of the gait. The proposed control policy goes behind the three primary principles: (i) The system’s switching surface has to be replaced by a new one if an external disturbance is induced. (ii) The new switching surface has to be reshaped back into its old style, together with the disturbance rejection. (iii) The stabilization procedure has to be performed with as small energy consumption as possible. Because of the reversibility effects of the switching surfaces in the above rules, the terminology of “Reversible Switching Surfaces” (RSS) is employed to address the control scheme; so the control objective would be the implementation of RSS for a bipedal robotic system. In this paper, this aim is achieved by a kinematically controlled foot scheme that is implemented on a simple structured biped. The presented idea is validated by a commercial version of MSC Adams software.

Effects of smartphone texting on the visual perception and dynamic walking stability.

Mobile phone use while walking can cause dual-task interference and increases safety risks by increasing attentional and cognitive demands. While the interference effect on cognitive function has been examined extensively, how perception of the environment and walking dynamics are affected by mobile phone use while walking is not well understood. The amount of visual information loss and its consequent impact on dynamic walking stability was examined in this study. Young adults (mean, 20.3 years) volunteered and walked on a treadmill while texting and attending to visual tasks simultaneously. Performance of visual task, field of regard loss, and margin of stability under dual-task conditions were compared with those of single-task conditions (i.e., visual task only). The results revealed that the size of visual field and visual acuity demand were varied across the visual task conditions. Approximately half of the visual cues provided during texting while walking were not perceived as compared to the visual task only condition. The field of regard loss also increased with increased dual-task cost of mobile phone use. Dynamic walking stability, however, showed no significant differences between the conditions. Taken together, the results demonstrate that the loss of situational awareness is unavoidable and occurs simultaneously with decrements in concurrent task performance. The study indicates the importance of considering the nature of attentional resources for the studies in dual-task paradigm and may provide practical information to improve the safe use of mobile phones while walking.

Fuzzy Control for Walking Balance of the Biped Robot Using ZMP Criterion

The dynamic walking stability of biped robot is a challenging research topic. In this paper, the fuzzy controller on zero movement point (ZMP) criterion is implemented to maintain the balance of dynamic walking. We designed a force sensitive resistor (FSR) sensor circuits to collect information from the sensors for the ZMP trajectory tracking. The robot walking has an imbalance when the ZMP shows the risk of moving out the footprint. The fuzzy controller is provided to drive the ZMP inside the ZMP reference area, by adjusting a suitable angle for the ankle and hip joint. In order to determine the ZMP reference, we compute the inverse kinematic and Jacobian coordinates from the biped robot model. In this research, we also introduce the biped robot configuration for control dynamic walking. A user interface is designed to conventionally observe the ZMP trajectory generation. The experimental results for stability of dynamic walking are presented to appreciate the proposed method.

Dynamic gait stability of treadmill versus overground walking in young adults

Treadmill has been broadly used in laboratory and rehabilitation settings for the purpose of facilitating human locomotion analysis and gait training. The objective of this study was to determine whether dynamic gait stability differs or resembles between the two walking conditions (overground vs. treadmill) among young adults. Fifty-four healthy young adults (age: 23.9±4.7years) participated in this study. Each participant completed five trials of overground walking followed by five trials of treadmill walking at a self-selected speed while their full body kinematics were gathered by a motion capture system. The spatiotemporal gait parameters and dynamic gait stability were compared between the two walking conditions. The results revealed that participants adopted a “cautious gait” on the treadmill compared with over ground in response to the possible inherent challenges to balance imposed by treadmill walking. The cautious gait, which was achieved by walking slower with a shorter step length, less backward leaning trunk, shortened single stance phase, prolonged double stance phase, and more flatfoot landing, ensures the comparable dynamic stability between the two walking conditions. This study could provide insightful information about dynamic gait stability control during treadmill ambulation in young adults.

EP 68. Stochastic resonance in the vestibular system

Stochastic resonance (SR) is a phenomenon, wherein the response of a nonlinear system to weak input signals can be optimized by addition of a particular non-zero level of noise. Here we tested for the presence of SR in the vestibular system by evaluating if a white noise galvanic vestibular stimulation (GVS) lowers the vestibular detection threshold. Sixteen healthy subjects (mean age 28.9 ± 2.0 years) participated in the study. Vestibular threshold detection was done by identifying the amplitude of a 1 Hz sinusoidal GVS (Digitimer, Hertfordshire, UK) at which subjects exhibit motion induced by the stimulation. Threshold detection was performed without and with an additional white noise GVS within a frequency range of 0–30 Hz and an amplitude set to 80% of the individual cutaneous threshold for GVS. Each threshold detection task consisted in ten bipolar sinusoidal GVS trials with amplitudes ranging from 0.1 μA to 1.9 μA (0.2 μA steps) while subjects sat on a chair with their eyes closed. Body motion was recorded via two inertial sensors (APDM, Inc., Portland, OR) fixed on the head and the trunk and motion responses were counted whenever the motion amplitude exceeded two standard deviations from mean calculated during a resting period preceding each stimulation trial. Body motion responses to stimulation were normalized with respect to the largest response value across all stimulation trials. A binomial distribution function was fit to the GVS amplitude and body response data and the detection was then determined as the stimulation amplitude at the point of subjective equality (i.e., a 50% chance of motion detection). The total of 20 stimulation trials was examined in a random order and subjects were blinded to the protocol. Individual detection thresholds without and with white noise GVS were compared using a paired samples t-test. White noise GVS significantly lowered vestibular detection thresholds from 1.02 ± 0.06 μA to 0.87 ± 0.04 μA (p = 0.011). The mean improvement was 7.9 ± 5.9%. White noise GVS has been previously found to improve cardiac function, postural control, and dynamic walking stability in healthy subjects and patients with bilateral vestibular dysfunction as well as Parkinson’s disease. The present findings indicate that the previously observed ameliorating effects of white noise GVS might result from an enhanced vestibular information processing and provide thereby first evidence for the presence of SR phenomena in the vestibular system.