Small directional treadmill perturbations induce differential gait stability adaptation

Effects of mediolateral whole-body vibration during gait with additional cognitive load

Whole-body vibration (WBV) may increase musculoskeletal disorder risk among workers standing on vibrating surfaces for prolonged periods. Limited studies were conducted to comprehend WBV impact on individuals engaged in dynamic activities. This study explored the effects of different horizontal WBV frequencies on gait parameters, lower limb kinematics, and the cognitive response of healthy subjects. Forty participants walked at constant speed on a treadmill mounted on a horizontal shaker providing harmonic vibration with an amplitude of 1 m/s2 and frequencies 2-10 Hz, with inversely proportional amplitudes. A Psychomotor Vigilance Test measured reaction time while a motion capture system recorded walking kinematics. ANOVA results revealed no significant impact of vibration frequencies on the reaction time. At 2 Hz, alterations in gait spatiotemporal parameters were significant, with reduced stride length, stride time, step length, and stance time and increased step width and cadence. Similarly, gait variability measured by standard deviation and coefficient of variation significantly increased at 2 Hz compared to the other conditions. Comparably, kinematic time series analyzed through statistical parametric mapping showed significant adjustments in different portions of the gait cycle at 2 Hz, including increased hip abduction and flexion, greater knee flexion around the heel strike, and augmented ankle dorsiflexion. Participants exhibited gait kinematic variations, mainly at 2 Hz, where the associated mediolateral displacement was higher, as a plausible strategy to maintain stability and postural control during perturbed locomotion. These findings highlight individuals' complex biomechanical adaptations in response to horizontal WBV, especially at lower frequencies, under dual-task conditions.

Individuals with knee osteoarthritis show few limitations in balance recovery responses after moderate gait perturbations

BACKGROUND

Knee osteoarthritis causes structural joint damage. The resultant symptoms can impair the ability to recover from unexpected gait perturbations. This study compared balance recovery responses to moderate gait perturbations between individuals with knee osteoarthritis and healthy individuals.

METHODS

Kinematic data of 35 individuals with end-stage knee osteoarthritis, and 32 healthy individuals in the same age range were obtained during perturbed walking on a treadmill at 1.0 m/s. Participants received anteroposterior (acceleration or deceleration) or mediolateral perturbations during the stance phase. Changes from baseline in margin of stability, step length, step time, and step width during the first two steps after perturbation were compared between groups using a linear regression model. Extrapolated center of mass excursion was descriptively analyzed.

FINDINGS

After all perturbation modes, extrapolated center of mass trajectories overlapped between individuals with knee osteoarthritis and healthy individuals. Participants predominantly responded to mediolateral perturbations by adjusting their step width, and to anteroposterior perturbations by adjusting step length and step time. None of the perturbation modes yielded between-group differences in changes in margin of stability and step width during the first two steps after perturbation. Small between-group differences were observed for step length (i.e. 2 cm) of the second step after mediolateral and anteroposterior perturbations, and for step time (i.e. 0.01-0.02 s) of first step after mediolateral perturbations and the second step after outward and belt acceleration perturbations.

INTERPRETATION

Despite considerable pain and damage to the knee joint, individuals with knee osteoarthritis showed comparable balance recovery responses after moderate gait perturbations to healthy participants.

A comparison of the effects of mediolateral surface and foot placement perturbations on balance control and response strategies during walking

BACKGROUND

Balance perturbation studies during walking have improved our understanding of balance control in various destabilizing conditions. However, it is unknown to what extent balance recovery strategies can be generalized across different types of mediolateral balance perturbations.

RESEARCH QUESTION

Do similar mediolateral perturbations (foot placement versus surface translation) have similar effects on balance control and corresponding balance response strategies?

METHODS

Kinetic and kinematic data were previously collected during two separate studies, each with 15 young, healthy participants walking on an instrumented treadmill. In both studies, medial and lateral balance perturbations were applied at 80% of the gait cycle either by a treadmill surface translation or a pneumatic force applied to the swing foot. Differences in balance control (frontal plane whole body angular momentum) and balance response strategies (hip abduction moment, ankle inversion moment, center of pressure excursion and frontal plane trunk moment) between perturbed and unperturbed gait cycles were evaluated using statistical parametric mapping.

RESULTS

Balance disruptions after foot placement perturbations were larger and sustained longer compared to surface translations. Changes in joint moment responses were also larger for the foot placement perturbations compared to the surface translation perturbations. Lateral hip, ankle, and trunk strategies were used to maintain balance after medial foot placement perturbations, while a trunk strategy was primarily used after surface translations.

SIGNIFICANCE

Surface and foot placement perturbations influence balance control and corresponding response strategies differently. These results can help inform the development of perturbation-based balance training interventions aimed at reducing fall risk in clinical populations.

A Wearable System for Continuous Monitoring and Assessment of Speech, Gait, and Cognitive Decline for Early Diagnosis of ADRD

Early detection of cognitive decline is essential to study mild cognitive impairment and Alzheimer's Disease in order to develop targeted interventions and prevent or stop the progression of dementia. This requires continuous and longitudinal assessment and tracking of the related physiological and behavioral changes during daily life. In this paper, we present a low cost and low power wearable system custom designed to track the trends in speech, gait, and cognitive stress while also considering the important human factor needs such as privacy and compliance. In the form factors of a wristband and waist-patch, this multimodal, multi-sensor system measures inertial signals, sound, heart rate, electrodermal activity and pulse transit time. A total power consumption of 2.6 mW without any duty cycling allows for more than 3 weeks of run time between charges when 1500 mAh batteries are used.Clinical Relevance- Much earlier detection of Alzheimer's disease and related dementias may be possible by continuous monitoring of physiological and behavioral state using application specific wearable sensors during the activities of daily life.

Classifying Unstable and Stable Walking Patterns Using Electroencephalography Signals and Machine Learning Algorithms

Analyzing unstable gait patterns from Electroencephalography (EEG) signals is vital to develop real-time brain-computer interface (BCI) systems to prevent falls and associated injuries. This study investigates the feasibility of classification algorithms to detect walking instability utilizing EEG signals. A 64-channel Brain Vision EEG system was used to acquire EEG signals from 13 healthy adults. Participants performed walking trials for four different stable and unstable conditions: (i) normal walking, (ii) normal walking with medial-lateral perturbation (MLP), (iii) normal walking with dual-tasking (Stroop), (iv) normal walking with center of mass visual feedback. Digital biomarkers were extracted using wavelet energy and entropies from the EEG signals. Algorithms like the ChronoNet, SVM, Random Forest, gradient boosting and recurrent neural networks (LSTM) could classify with 67 to 82% accuracy. The classification results show that it is possible to accurately classify different gait patterns (from stable to unstable) using EEG-based digital biomarkers. This study develops various machine-learning-based classification models using EEG datasets with potential applications in detecting unsteady gait neural signals and intervening by preventing falls and injuries.

Speeding up: Discrete mediolateral perturbations increased self-paced walking speed in young and older adults

BACKGROUND

In uncertain environments and with increasing age, humans often walk, slower while taking shorter, quicker, and wider steps, reflective of a cautious gait., Understanding when humans opt to use a cautious gait and the differences in gait, strategies used as people age could be examined with perturbations on a self-paced, treadmill that allows participants to adjust their walking speed. Adding varying degrees, of unpredictability, an inherent element of real-world walking, could also improve, understanding of when specific gait strategies are used RESEARCH QUESTION: We investigated how healthy young and older adults adjust their, gait strategies when responding to perturbations of varying unpredictability. We, hypothesized that more unpredictable perturbations would produce more cautious gait, strategies and be more pronounced in older adults than young adults METHODS: Ten young and ten older adults walked on a self-paced treadmill with, discrete mediolateral treadmill shift perturbations. We changed the shift magnitude, and/or the timing of the perturbations during the gait cycle to vary perturbation, unpredictability. We analyzed walking speed and step kinematics from treadmill and, motion capture data RESULTS: Surprisingly, participants walked faster, not slower, for the conditions with, perturbations. Even more surprising, older adults walked faster overall than young, adults. As expected, participants took faster and wider steps for the most unpredictable, perturbation but also took longer steps, which was not expected. Step kinematic, variability and average step width also increased as perturbation unpredictability, increased, suggesting that the more unpredictable conditions demanded greater, balance control. Additionally, older adults had greater step kinematic variability, highlighted further using detrended step length variability, compared to young adults SIGNIFICANCE: Overall, these findings provide new insights about gait strategies and, suggest that perturbations such as discrete mediolateral treadmill shifts can potentially, be designed to encourage participants to walk faster, if it is beneficial.

Rethinking margin of stability: Incorporating step-to-step regulation to resolve the paradox

Derived from inverted pendulum dynamics, mediolateral Margin of Stability (MoSML) is a mechanically-grounded measure of instantaneous frontal-plane stability. However, average MoSML measures yield paradoxical results. Gait pathologies or perturbations often induce larger (supposedly "more stable") average MoSML, despite clearly destabilizing factors. However, people do not walk "on average" - they walk (and sometimes lose balance) one step at a time. We assert the paradox arises because averaging MoSML discards crucial step-to-step dynamics. We present a framework unifying the inverted pendulum with Goal-Equivalent Manifold (GEM) analyses. We identify in the pendulum's center-of-mass dynamics constant-MoSML manifolds, including one candidate "stability GEM" signifying the goal to maintain some constant MoSML∗. We used this framework to assess step-to-step MoSML dynamics of humans walking in destabilizing environments. While goal-relevant deviations were readily corrected, people did not exploit equifinality by allowing deviations to persist along this GEM. Thus, maintaining a constant MoSML∗ is inconsistent with observed step-to-step fluctuations in center-of-mass states. Conversely, the extent to which participants regulated fluctuations in mediolateral foot placements strongly predicted their regulation of center-of-mass fluctuations. Thus, center-of-mass dynamics may arise indirectly as a consequence of regulating mediolateral foot placements. To help resolve the paradox caused by averaging MoSML, we present a new statistic, Probability of Instability (PoIL), used here to predict lateral instability likelihood. Participants exhibited increased PoIL when destabilized (p = 9.45 × 10-34), despite exhibiting larger ("more stable") average MoSML (p = 1.70 × 10-15). Thus, PoIL correctly captured people's increased risk of losing lateral balance, whereas average MoSML did not. PoIL also helps explain why people's average MoSML increased in destabilizing contexts.

Different Types of Mastoid Process Vibrations Affect Dynamic Margin of Stability Differently

The vestibular system is critical for human locomotion. Any deteriorated vestibular system leads to gait instability. In the past decades, these alternations in gait patterns have been majorly measured by the spatial-temporal gait parameters and respective variabilities. However, measuring gait characteristics cannot capture the full aspect of motor controls. Thus, to further understand the effects of deteriorated vestibular system on gait performance, additional measurement needs to be taken into consideration. This study proposed using the margin of stability (MOS) to identify the patterns of dynamic control under different types of mastoid vibrations in walking. This study hypothesized that (1) using the MOS method could facilitate the understanding of another aspect of motor control induced by different types of mastoid vibrations, and (2) applying the mastoid vibrations could induce the asymmetric MOS. Twenty healthy young adults were recruited. Two electromechanical vibrotactile transducers were placed on the bilateral mastoid process to apply different types of vestibular vibrations (bilateral, unilateral, and no vibration). A motion capture system with eight cameras was used to measure the MOSap (margin of stability in the anterior-posterior direction), MOSml (margin of stability in the medial-lateral direction), and respective variabilities. The results were in line with the hypotheses that both bilateral and unilateral mastoid vibrations significantly increased MOSap (p = 0.036, p < 0.001), MOSml (p = 0.012, p < 0.001), and respective variabilities p = 0.001, p < 0.001; p = 0.001, p < 0.01 when compared to the no vibration condition. Also, significantly larger MOSml (p = 0.001), MOSml variability (p < 0.023), MOSap (p < 0.001), and MOSap variability (p = 0.002) were observed under the unilateral vibration condition than that observed under the bilateral vibration condition. The above-mentioned result found that different types of mastoid vibrations affected the MOS differently, suggesting different patterns of control mechanisms under different sensory-conflicted situations. Besides, a significant difference between the dominant and non-dominant legs was observed in MOSml. Moreover, applying the unilateral mastoid vibrations induced a greater symmetric index of MOSml, suggesting that more active control in balance was needed in the medial-lateral than in the anterior-posterior direction.

Which lower limb joints compensate for destabilizing energy during walking in humans?

Current approaches to investigating stabilizing responses during locomotion lack measures that both directly relate to perturbation demands and are shared across different levels of description (i.e. joints and legs). Here, we investigated whether mechanical energy could serve as a 'common currency' during treadmill walking with transient unilateral belt accelerations. We hypothesized that by delivering perturbations in either early or late stance, we could elicit net negative or positive work, respectively, from the perturbed leg at the leg/treadmill interface, which would dictate the net demand at the overall leg level. We further hypothesized that of the lower limb joints, the ankle would best reflect changes in overall leg work. On average across all seven participants and 222 perturbations, we found early stance perturbations elicited no change in net work performed by the perturbed leg on the treadmill, but net positive work by the overall leg, which did not support our hypotheses. Conversely, late stance perturbations partially supported our hypotheses by eliciting positive work at the leg/treadmill interface, but no change in net work by the overall leg. In support of our final hypothesis, changes in perturbed ankle work, in addition to contralateral knee work, best reflected changes in overall leg work.