Subsensory vibrations to the feet reduce gait variability in elderly fallers

What are the temporal and physical characteristics of locally applied vibration that modulate balance in older adults? - A systematic review of the literature

BACKGROUND

Compromised balance is known to contribute to falls, which are associated with increased morbidity and mortality for older adults. Evidence suggests that the application of local vibration to the lower limbs of older adults has the potential to modulate balance.

RESEARCH QUESTION

To identify the temporal and mechanical parameters of vibration applied locally to the lower limbs of older adults that modulate measures of balance, and to define the short- and long-term effects of vibration on balance in this population.

METHODS

The PRISMA 2020 guidelines were used to conduct a systematic search including the PUBMED, EMBASE, and Scopus databases to identify peer-reviewed literature where vibration was applied to the lower limbs of older adults to modulate balance. Data was extracted using a study-specific data extraction form and risk of bias assessed. Where possible, effect sizes were calculated.

RESULTS

Of 7777 records screened, ten randomised controlled trials and 43 prospective laboratory-based studies met the inclusion criteria. Vibration frequencies ranged from 1 to 272 Hz, most studies (n=41) used ≤100 Hz. Amplitude ranged from 0.2 to 3.0 mm, most studies (n=28) used ≤1 mm. Effects of short-term vibration (applied for seconds to hours) were measured during and/or immediately after application. Short-term suprathreshold perceived muscle/tendon vibration had a 'large' destabilising effect size on balance in healthy older adults, but little or no effect on older fallers. Short-term subthreshold vibration to the soles of the feet had a 'small' stabilising effect size. Suprathreshold muscle, tendon or sole vibration applied for 10-30 min over days to weeks improved balance measures, but most (8 of 10) had increased risk of bias.

SIGNIFICANCE

The heterogeneity of methodology, populations, and vibration and balance parameters precluded conclusions about the relative effects of lower limb vibration in older adults. However, these results suggest that the application of local vibration to the lower limbs of older adults can modulate balance in the short- and long-term.

The effects of vibrating shoe insoles on standing balance, walking, and ankle-foot muscle activity in adults with diabetic peripheral neuropathy

BACKGROUND

Peripheral neuropathy is one of the most common complications of type 2 diabetes, which can lead to impaired balance and walking. Innovative footwear devices designed to stimulate foot sensory receptors, such as vibrating insoles, could offer a new route to improve motor impairments in people with diabetic peripheral neuropathy (DPN).

RESEARCH QUESTION

Does wearing vibrating insoles for the first time alter measures of balance, walking, and ankle-foot muscle activity, in people with DPN?

METHODS

A randomised cross-over study was conducted with 18 ambulant men and women with a diagnosis of DPN. Participants performed tests of standing balance (Bertec® force platform) under four conditions (foam/firm surface, eyes open/closed) and level-ground walking (GAITRite® instrumented walkway), whilst wearing vibrating and non-vibrating (control) insoles on two separate occasions (one insole/session). Electromyography (EMG) was used to assess soleus, medial gastrocnemius, tibialis anterior, peroneus longus activity during balance tests. Outcomes included centre of pressure (CoP) sway, EMG amplitude, spatiotemporal gait patterns, and Timed Up and Go test. One sample t-tests were used to explore %differences in outcomes between insole conditions.

RESULTS

Wearing vibrating insoles led to a reduction (improvement) in CoP elliptical area, when standing on a foam surface with eyes closed, relative to non-vibrating insoles (P=0.03). Applying perceptible vibrations to the soles of the feet also reduced the EMG amplitude in soleus (P=0.01 and P=0.04) and medial gastrocnemius (P=0.03 and P=0.09) when standing with eyes closed on firm and foam surfaces.

SIGNIFICANCE

Our findings of signs of improved balance and altered muscle activity with suprasensory vibrating insoles provides new insights into how these devices can be used to inform innovative rehabilitation approaches in individuals with DPN. This will be strengthened by further research into possible clinical benefits of these devices - given that the effects we detected were small with uncertain clinical meaning.

Application of vibration to the soles increases long-range correlations in the stride parameters during walking

Temporal fluctuations in the stride parameters during human walking exhibit long-range correlations, but these long-range correlations in the stride parameters decrease due to aging or neuromuscular diseases. These observations suggest that any quantified index of the long-range correlation can be regarded as an indicator of gait functionality. Considering the effect of task-relevant sensory feedback on augmenting human motor performance, we devised shoes with active insoles that could deliver noisy vibration to the soles of feet and assessed their efficacy in enhancing the long-range correlations in the stride parameters for healthy young adults. The vibration could be wirelessly controlled using a smartphone. The actuators, control unit, and battery in the devised shoes were light and embedded in the shoes. By virtue of this compactness, the shoes could be easily used for daily walking outside a laboratory. We performed walking experiments with 20 healthy adults and evaluated the effects of sub- and supra-threshold vibration on long-range correlations in stride interval and length. We performed detrended fluctuation analysis to quantify the long-range correlation of temporal changes in stride interval and length. We found that supra-threshold vibration, applied to the soles with the amplitude of 130 % of the sensory threshold, significantly increased the long-range correlations in stride interval and length by 10.3 % (p = 0.009) and 10.1 % (p = 0.021), respectively. On the other hand, sub-threshold vibration with the amplitude of 90 % of the sensory threshold had no significant effect. These results demonstrate that additional somatosensory feedback through barely detectable vibrations, which are supplied by compact shoes with active insoles, can enhance the indices of "healthy" complexity of locomotor function.

Subthreshold electrical noise alters walking balance control in individuals with cerebral palsy

BACKGROUND

Sensory deficits in individuals with cerebral palsy (CP) play a critical role in balance control. However, there is a lack of effective interventions that address sensory facilitation to improve walking balance. Stochastic Resonance (SR) stimulation involves delivering sub threshold noise to improve balance in patients with sensory deficits by enhancing the detection of sensory input.

RESEARCH QUESTION

To investigate the immediate effects of SR on walking balance in individuals with and without CP.

METHODS

Thirty-four participants (17 CP, 17 age-and sex-matched typically developing controls or TD) between 8 and 24 years of age were recruited. SR stimulation was applied to the muscles and ligaments of ankle and hip joint. An optimal SR intensity during walking was determined for each subject. Participants walked on a self-paced treadmill for three trials of two minutes each using a random order of SR stimulation (SR) and no stimulation (noSR) control conditions. Our primary outcome measure was minimum lateral margin of stability (MOS). Secondary outcome measures include anterior MOS before heelstrike and spatiotemporal gait parameters. We performed two-way mixed ANOVAs with group (CP, TD) as between-subject and condition (noSR, SR) as within subject factors.

RESULTS

Compared to walking without SR, there was a small but significant increase in the lateral and anterior MOS with SR stimulation, implying that a larger impulse was needed to become unstable, in turn implying higher stability. Step width and step ength decreased with SR for the CP group with SR stimulation. There were no significant effects for other spatiotemporal variables.

SIGNIFICANCE

Sub threshold electrical noise can slightly improve walking balance control in individuals with CP. SR stimulation, through enhanced proprioception, may have improved the CP group's awareness of body motion during walking, thus leading them to adopt a more conservative stability strategy to prevent a potential fall.

The effect of mechanical vibration-based stimulation on dynamic balance control and gait characteristics in healthy young and older adults: A systematic review of cross-sectional study

BACKGROUND

A good dynamic balance control and stable gait played an important role in the daily ambulation, especially for older adults with sensorimotor degeneration. This study aimed to systematically review the effects and potential mechanisms of mechanical vibration-based stimulation (MVBS) on dynamic balance control and gait characteristics in healthy young and older adults.

METHOD

Five bioscience and engineering databases, including MEDLINE via PubMed, CINAHL via EBSCO, Cochrane Library, Scopus, and Embase, were searched until September 4th, 2022. Studies published between 2000 and 2022 in English and Chinese involving mechanical vibration related to gait and dynamic balance were included. The procedure was followed via the preferred reporting items for systematic reviews and meta-analysis method. The methodological quality of included studies was assessed using the NIH study quality assessment tool for observational cohort and cross-sectional studies.

RESULTS

A total of 41 cross-sectional studies met the inclusion criteria and were included in this study. Eight studies were good-quality while 26 were moderate-quality and 7 were poor-quality. There were six categories of MVBS at various frequencies and amplitudes utilized in included studies, including plantar vibration, focal muscle vibration, Achilles tendon vibration, vestibular vibration, cervical vibration, and vibration on nail of hallux.

SIGNIFICANCE

Different types of MVBS targeting different sensory systems affected the dynamic balance control and gait characteristics differently. MVBS could be used to provide improvement or perturbation to specific sensory systems, to induce different sensory reweight strategies during gait.

The Effect of Human Settlement Pedestrian Environment on Gait of Older People: An Umbrella Review

Older people are limited by the pedestrian environment in human settlements and are prone to travel difficulties, falls, and stumbles. Furthermore, we still lack systematic knowledge of the pedestrian environment affecting the gait of older people. The purpose of this review is to synthesize current evidence of effective human settlement pedestrian environments interfering with gait in older people. The systematic effects of the human settlement pedestrian environment on gait in older people are discussed. Databases such as Web of Science, Medline (via PubMed), Scopus, and Embase were searched for relevant studies up to June 2022. The literature was screened to extract relevant evidence from the included literature, assess the quality of the evidence, and analyze the systematic effects of the pedestrian environment on gait in older people. From the 4297 studies identified in the initial search, 11 systematic reviews or meta-analysis studies were screened, from which 18 environmental factors and 60 gait changes were extracted. After removing duplicate elements and merging synonymous features, a total of 53 relationships between environmental factors and gait change in older people were extracted: the main human settlement pedestrian environmental factors affecting gait change in older people in existing studies were indoor and outdoor stairs/steps, uneven and irregular ground, obstacles, walking path turns, vibration interventions, mechanical perturbation during gait, and auditory sound cues. Under the influence of these factors, older people may experience changes in the degree of cautiousness and conservatism of gait and stability, and their body posture performance and control, and muscle activation may also be affected. Factors such as ground texture or material, mechanical perturbations during gait, and vibration interventions stimulate older people's understanding and perception of their environment, but there is controversy over the results of specific gait parameters. The results support that human settlements' pedestrian environment affects the gait changes of older people in a positive or negative way. This review may likely contribute evidence-based information to aid communication among practitioners in public health, healthcare, and environmental construction. The above findings are expected to provide useful preference for associated interdisciplinary researchers to understand the interactions among pedestrian environments, human behavior, and physiological characteristics.

Different types of plantar vibration affect gait characteristics differently while walking on different inclines

Background

Plantar vibration has been widely used to strengthen the sensation of the somatosensory system, further enhancing balance during walking on a level surface in patients with stroke. However, previous studies with plantar vibration only involved the level surface, which neglected the importance of inclined/declined walking in daily life. Thus, combining the plantar vibration and inclined/declined walking might answer a critical research question: whether different types of plantar vibration had different effects on gait characteristics during walking on different inclines.

Methods

Eighteen healthy young adults were recruited. Fifteen walking conditions were assigned randomly to these healthy adults (no, sub-, and supra-threshold plantar vibration × five different inclines: +15%, +8%, 0%, -8%, -15% grade). A motion capture system with eight cameras captured 12 retro-reflective markers and measured the stride time, stride length, step width, and respective variabilities.

Results

A significant interaction between vibration and inclination was observed in the stride time (p < 0.0001) and step width (p = 0.015). Post hoc comparisons found that supra-threshold vibration significantly decreased the stride time (-8%: p < 0.001; -15%: p < 0.001) while the sub-threshold vibration significantly increased the step width (-8%: p = 0.036) in comparison with no plantar vibration.

Conclusions

When walking downhill, any perceivable (supra-threshold) vibration on the plantar area decreased the stride time. Also, the increase in step width was observed by non-perceivable (sub-threshold) plantar vibration while walking uphill. These observations were crucial as follows: (1) applying sub-threshold plantar vibrations during uphill walking could increase the base of support, and (2) for those who may need challenges in locomotor training, applying supra-threshold vibration during downhill walking could reach this specific training goal.

Effects of Vibration Direction and Pressing Force on Finger Vibrotactile Perception and Force Control

This paper reports about the effects of vibration direction and finger-pressing force on vibrotactile perception, with the goal of improving the effectiveness of haptic feedback on interactive surfaces. An experiment was conducted to assess the sensitivity to normal or tangential vibration at 250 Hz of a finger exerting constant pressing forces of 0.5 or 4.9 N. Results show that perception thresholds for normal vibration depend on the applied pressing force, significantly decreasing for the stronger force level. Conversely, perception thresholds for tangential vibrations are independent of the applied force, and approximately equal the lowest thresholds measured for normal vibration.

Location-specific cutaneous electrical stimulation of the footsole modulates corticospinal excitability to the plantarflexors and dorsiflexors during standing

Non‐noxious electrical stimulation to distinct locations of the foot sole evokes location‐specific cutaneous reflex responses in lower limb muscles. These reflexes occur at latencies that may enable them to be mediated via a transcortical pathway. Corticospinal excitability to the plantarflexors and dorsiflexors was measured in 16 participants using motor evoked potentials (MEPs). Spinal excitability was measured in eight of the original participants using cervicomedullary motor evoked potentials (CMEPs). Measurements were collected with and without preceding cutaneous stimulus to either the heel (HEEL) or metatarsal (MET) locations of the foot sole, and evoked potentials were elicited to coincide with the arrival of the cutaneous volley at either the motor cortex or spinal cord. Plantarflexor MEPs and CMEPs were facilitated with cutaneous stimulation to the HEEL for MEPs (soleus p = 0.04, medial gastrocnemius (MG) p = 0.017) and CMEPs (soleus p = 0.047 and MG p = 0.015), but they were unchanged following MET stimulation for MEPs or CMEPs. Dorsiflexor MEPs were unchanged with cutaneous stimulation at either location, but dorsiflexor CMEPs increased with cutaneous stimulation (p = 0.05). In general, the increase in CMEP amplitudes was larger than the increase in MEP amplitudes, indicating that an increase in spinal excitability likely explains most of the increase in corticospinal excitability. The larger change observed in the CMEP also indicates that excitability from supraspinal sources likely decreased, which could be due to a net change in the excitability of intracortical circuits. This study provides evidence that cutaneous reflexes from foot sole skin are likely influenced by a transcortical pathway.

Application of vibration to the soles reduces minimum toe clearance variability during walking

Minimum toe clearance (MTC) is an important indicator of the risk of tripping. Aging and neuromuscular diseases often decrease MTC height and increase its variability, leading to a higher risk of tripping. Previous studies have developed visual feedback-based gait training systems to modify MTC. However, these systems are bulky and expensive, and the effects of the training continue only for a short time. We paid attention to the efficacy of vibration in decreasing the variability of gait parameters, and hypothesized that proper vibration applied to soles can reduce the MTC variability. Using shoes embedded with active vibrating insoles, we assessed the efficacy of both sub- and supra-threshold vibration in affecting MTC distribution. Experiment results with 17 young and healthy adults showed that vibration applied throughout the walking task with constant intensity of 130% of sensory threshold significantly decreased MTC variability, whereas sub-threshold vibration yielded no significant effect. These results demonstrate that a properly designed tactile sensory input which is controlled and delivered by a simple wearable device, the active insole, can reduce the MTC variability during walking.

Improvement of Gait in Patients with Stroke Using Rhythmic Sensory Stimulation: A Case-Control Study

Patients with stroke suffer from impaired locomotion, exhibiting unstable walking with increased gait variability. Effects of rhythmic sensory stimulation on unstable gait of patients with chronic stroke are unclear. This study aims to determine the effects of rhythmic sensory stimulation on the gait of patients with chronic stroke. Twenty older adults with stroke and twenty age- and gender-matched healthy controls walked 60 m under four conditions: normal walking with no stimulation, walking with rhythmic auditory stimulation (RAS) through an earphone in the ear, walking with rhythmic somatosensory stimulation (RSS) through a haptic device on the wrist of each participant, and walking with rhythmic combined stimulation (RCS: RAS + RSS). Gait performance in the stroke group significantly improved during walking with RAS, RSS, and RCS compared to that during normal walking (p < 0.008). Gait variability significantly decreased under the RAS, RSS, and RCS conditions compared to that during normal walking (p < 0.008). Rhythmic sensory stimulation is effective in improving the gait of patients with chronic stroke, regardless of the type of rhythmic stimuli, compared to healthy controls. The effect was greater in patients with reduced mobility, assessed by the Rivermead Mobility Index (RMI).

The effects of mechanical noise bandwidth on balance across flat and compliant surfaces

Although the application of sub-sensory mechanical noise to the soles of the feet has been shown to enhance balance, there has been no study on how the bandwidth of the noise affects balance. Here, we report a single-blind randomized controlled study on the effects of a narrow and wide bandwidth mechanical noise on healthy young subjects’ sway during quiet standing on firm and compliant surfaces. For the firm surface, there was no improvement in balance for both bandwidths—this may be because the young subjects could already balance near-optimally or optimally on the surface by themselves. For the compliant surface, balance improved with the introduction of wide but not narrow bandwidth noise, and balance is improved for wide compared to narrow bandwidth noise. This could be explained using a simple model, which suggests that adding noise to a sub-threshold pressure stimulus results in markedly different frequency of nerve impulse transmitted to the brain for the narrow and wide bandwidth noise—the frequency is negligible for the former but significantly higher for the latter. Our results suggest that if a person’s standing balance is not optimal (for example, due to aging), it could be improved by applying a wide bandwidth noise to the feet.

Reducing the foot trajectory variabilities during walking through vibratory stimulation of the plantar surface of the foot

Variabilities or fluctuations in foot clearance are considered as a risk factor for falls during walking in older adults. The present study aimed to investigate whether the foot trajectory variability can be reduced by applying vibratory stimulation to the foot's plantar surface during walking. Ten healthy adults were asked to walk on a treadmill with vibratory shoes, and body kinematics were measured. Changes in the mean absolute deviations of the foot trajectory and joint and trunk angles were compared between the periods of applied or absent vibratory stimulus. Our results demonstrated that toe trajectory variability in the swing phase was significantly smaller when a vibratory stimulus was applied. Applying vibratory stimulus to the soles of the forefoot could potentially be used to reduce foot trajectory variability, which could reduce the risk of trips and associated falls during walking in older adults.

Can Insoles Be Used to Improve Static and Dynamic Balance of Community-Dwelling Older Adults? A Systematic Review on Recent Advances and Future Perspectives

This systematic review investigated the effects of orthopedic, vibrating, and textured insoles on the postural balance of community-dwelling older adults. Articles published in English from 1999 to 2019 investigating the effects of (a) orthopedic, (b) vibrating, and (c) textured insoles on static and dynamic balance in community-dwelling older adults were considered. Twenty-four trials with a total of 634 older adults were identified. The information gathered generally supported the balance-improving effects of orthopedic, vibrating, and textured insoles in both static and dynamic conditions among community-dwelling older adults. Further examination found that rigidity, texture patterns, vibration thresholds, and components like arch supports and heel cups are important factors in determining whether insoles can improve balance. This review highlights the potential of insoles for improving the static and dynamic balance of community-dwelling older adults. Good knowledge in insole designs and an understanding of medical conditions of older adults are required when attempts are made to improve postural balance using insoles.

Stochastic Resonance Reduces Sway and Gait Variability in Individuals With Unilateral Transtibial Amputation: A Pilot Study

Sub-threshold (imperceptible) vibration, applied to parts of the body, impacts how people move and perceive our world. Could this idea help someone who has lost part of their limb? Sub-threshold vibration was applied to the thigh of the affected limb of 20 people with unilateral transtibial amputation. Vibration conditions tested included two noise structures: pink and white. Center of pressure (COP) excursion (range and root-mean-square displacements) during quiet standing, and speed and spatial stride measures (mean and standard deviations of step length and width) during walking were assessed. Pink noise vibration decreased COP displacements in standing, and white noise vibration decreased sound limb step length standard deviation in walking. Sub-threshold vibration positively impacted aspects of both posture and gait; however, different noise structures had different effects. The current study represents foundational work in understanding the potential benefits of incorporating stochastic resonance as an intervention for individuals with amputation.

Subthreshold Electrical Noise Applied to the Plantar Foot Enhances Lower-Limb Cutaneous Reflex Generation

Reflex responses generated by cutaneous mechanoreceptors of the plantar foot are important for the maintenance of balance during postural tasks and gait. With aging, reflex generation, particularly from fast adapting type I receptors, is reduced, which likely contributes to impaired postural stability in this population. Therefore, improving reflex generation from these receptors may serve as a tool to improve balance performance. A mechanism to enhance reflexes may lie in the phenomenon of stochastic resonance, whereby the addition of certain intensities and frequencies of noise stimuli improves the performance of a system. This study was conducted to determine whether tactile noise stimuli could improve cutaneous reflex generation. In 12 healthy young adults, we evoked cutaneous reflex responses using a 0–50 Hz Gaussian noise vibration applied to the plantar heel. Concurrently, we applied one of six subthreshold intensities of electrical tactile noise to the plantar heel [0%, 20%, 40%, 60%, 80% or 100% (threshold)] and were able to analyze data from 0%, 20% and 40% trials. Across participants, it was found that the addition of a 20% perceptual threshold (PT) noise resulted in enhanced reflex responses when analyzed in both the time and frequency domains. These data provide evidence that cutaneous reflex generation can be enhanced via a stochastic resonance effect and that 20% PT is the optimal intensity of noise to do so. Therefore, the addition of noise stimuli may be a valuable clinical intervention to improve reflex responses associated with postural balance in populations with impairments.

Mini-Logger- A Wearable Inertial Measurement Unit (IMU) for Postural Sway Analysis

Postural instability assessment is an important tool in fall risk analysis and for timely intervention of falls to reduce or prevent fall injuries. Traditionally fall risk is measured though postural sway assessment and is collected through forceplates by mapping Center of Pressure (COP) excursions or using motion analysis camera system for marker sway trajectories. However, both of these systems are expensive and lack portability to their usage in clinical environments. In this study, we developed a novel wearable low-cost MEMS inertial sensor and validated its usage for human postural sway assessment in standing posture with eyes open/closed, vibration/no vibration, and proprioception /low proprioception conditions. The two objectives of this study were: 1) To develop and validate an Inertial Measurement Unit (IMU) for sway analysis 2) To determine the feasibility of the system in detecting human postural imbalances such as reduced proprioception or presence of stochastic resonance induced through subthreshold vibrations on the feet. The novel IMU was tested for sway against infra-red marker on a specialized platform with 4-degrees of freedom. Many parameters of postural sway such as sway velocity, Root Mean Square (RMS), and sway path length could successfully detect subtle postural changes due to varying proprioceptive and sub-threshold vibration conditions. We found agreement in sway signal determinism from the two methods.Clinical Relevance- This wearable sensor technology has potential to determine balance in reliable, easy and accurate way in clinical environments.

Effect of Adding Proprioceptive Exercise to Balance Training in Older Adults with Diabetes: A Systematic Review

INTRODUCTION

Accidental fall is a serious problem in older adults. The incidence of accidental fall increases by any dysfunction in the proprioceptive system. The function of the proprioceptive system usually is much affected in people with Diabetes Mellitus (DM), particularly in older ages. However, proprioceptive exercise significantly improves the balance control in older adults, no systematic review demonstrated its effectiveness in improving the balance control in older adults with DM. Thus, this systematic review was conducted to examine the effectiveness of adding proprioceptive exercise to any balance training in older adults with DM.

METHODS

A systematic search was performed in five major databases. The inclusion criteria of this search included older adults with DM, peripheral neuropathy, randomized control trial, and proprioceptive dysfunction. The exclusion criterion of this search included any study where participants had a history of a disease that might affect the balance control such as ataxia, stroke, and Parkinsonism. The outcome of interest was the importance of including proprioceptive exercise in increasing the effectiveness of balance training in older adults with DM.

RESULTS

Nine RCTs met the inclusion criteria for this systematic review. Seven studies of these nine studies included randomization details. Only two studies included the blindness, and only one of them included double blindness. The description of the withdrawal of participants was shown in eight studies. All the included studies used a control group and accomplished the homogeny between subjects in the both groups.

CONCLUSION

This systematic review showed that proprioceptive exercise is a vital component that should be included in any balance training to gain short-term improvement in the balance control in older adults with DM.

Postural Control Underlying Head Movements While Tracking Visual Targets

The aim of this study was to investigate the relationship between postural regulation and tracking accuracy under static and moving visual target conditions in unipedal and bipedal standing postures. Postural time-to-contact stability boundaries decreased under more challenging visual target conditions for the unipedal posture, but this decrease was associated with lower visual tracking error. During bipedal support, there was independent control of the head and foot center of pressure, as higher frequencies at the head during the static visual task were associated with longer time-to-contact. These results demonstrate that decreased time-to-contact stability boundaries is a functional adaptation in postural tasks requiring visual control and provide evidence of the dependency of postural control on the nature of the suprapostural task.

The effects of sub-threshold vibratory noise on visuomotor entrainment during human walking and standing in a virtual reality environment

Humans will naturally synchronize their posture to the motion of a visual surround, but it is unclear if this visuomotor entrainment can be attenuated with an increased sensitivity to somatosensory information. Sub-threshold vibratory noise applied to the Achilles tendons has proven to enhance ankle proprioception through the phenomenon of stochastic resonance. Our purpose was to compare visuomotor entrainment during walking and standing, and to understand how this entrainment might be attenuated by applying sub-threshold vibratory noise over the Achilles tendons. We induced visuomotor entrainment during standing and treadmill walking for ten subjects (24.5 ± 2.9 years) using a speed-matched virtual hallway with continuous mediolateral perturbations at three different frequencies. Vibrotactile motors over the Achilles tendons provided noise (0-400 Hz) with an amplitude set to 90% of each participant's sensory threshold. Mediolateral sacrum, C7, and head motion was greatly amplified (4-8× on average) at the perturbation frequencies during walking, but was much less pronounced during standing. During walking, individuals with greater mediolateral head motion at the fastest perturbation frequency saw the greatest attenuation of that motion with applied noise. Similarly, during standing, individuals who exhibited greater postural sway (as measured by the center of pressure) also saw the greatest reductions in sway with sub-threshold noise applied in three of our summary metrics. Our results suggest that, at least for healthy young adults, sub-threshold vibratory noise over the Achilles tendons can slightly improve postural control during disruptive mediolateral visual perturbations, but the applied noise does not substantially attenuate visuomotor entrainment during walking or standing.

Fractal fluctuations in exploratory movements predict differences in dynamic touch capabilities between children with Attention-Deficit Hyperactivity Disorder and typical development

Children with Attention-Deficit Hyperactivity Disorder (ADHD) struggle to perform a host of daily activities. Many of these involve forceful interaction with objects and thus implicate dynamic touch. Therefore, deficits in dynamic touch could underlie functional difficulties presented by ADHD children. We investigated whether performance on a dynamic touch task (length perception by wielding) differ between children with ADHD and age-matched controls. We further examined whether this difference could be explained by fractal temporal correlations (wielding dynamics). Forty-two children (ADHD: 21; typically developing: 21) wielded unseen wooden rods and reported their perceived length in the form of magnitude productions. The rods varied in the magnitude of the first principal moment of inertia (I₁). Three-dimensional displacements of hand and rod positions were submitted to Detrended Fluctuation Analysis to estimate trial-by-trial temporal correlations. Children with ADHD reported shorter length for rods with higher I₁ than their typically developing peers, indicative of reduced sensitivity to mechanical information supporting dynamic touch. Importantly, temporal correlations in wielding dynamics moderated children’s usage of I_1. This finding points to a role of exploratory movements in perceptual deficits presented by children with ADHD and, thus, should be considered a new potential target for interventions.

The Promise of Stochastic Resonance in Falls Prevention

Multisensory integration is essential for maintenance of motor and cognitive abilities, thereby ensuring normal function and personal autonomy. Balance control is challenged during senescence or in motor disorders, leading to potential falls. Increased uncertainty in sensory signals is caused by a number of factors including noise, defined as a random and persistent disturbance that reduces the clarity of information. Counter-intuitively, noise can be beneficial in some conditions. Stochastic resonance is a mechanism whereby a particular level of noise actually enhances the response of non-linear systems to weak sensory signals. Here we review the effects of stochastic resonance on sensory modalities and systems directly involved in balance control. We highlight its potential for improving sensorimotor performance as well as cognitive and autonomic functions. These promising results demonstrate that stochastic resonance represents a flexible and non-invasive technique that can be applied to different modalities simultaneously. Finally we point out its benefits for a variety of scenarios including in ambulant elderly, skilled movements, sports and to patients with sensorimotor or autonomic dysfunctions.

Influence of Piano Key Vibration Level on Players’ Perception and Performance in Piano Playing

In this study, the influence of piano key vibration levels on players’ personal judgment of the instrument quality and on the dynamics and timing of the players’ performance of a music piece excerpt is examined. In an experiment four vibration levels were presented to eleven pianists playing on a digital grand piano with grand piano-like key action. By evaluating the players’ judgment of the instrument quality, strong integration effects of auditory and tactile information were observed. Differences in the sound of the instrument were perceived by the players, when the vibration level in the keys was changed and the results indicate a sound-dependent optimum of the vibration levels. By analyzing the influence of the vibration levels on the timing and dynamics accuracy of the pianists’ musical performances, we could not observe systematic differences that depend on the vibration level.

Stochastic resonance improves visuomotor temporal integration in healthy young adults

Mechanical and electrical noise stimulation to the body is known to improve the sensorimotor system. This improvement is related to stochastic resonance (SR), a phenomenon described as a "noise benefit" to various sensory and motor systems. The current study investigated the influence of SR on visuomotor temporal integration and hand motor function under delayed visual feedback in healthy young adults. The purpose of this study was to measure the usefulness of SR as a neurorehabilitation device for disorders of visuomotor temporal integration. Thirty healthy volunteers underwent detection tasks and hand motor function tests under delayed visual feedback, with or without SR. Of the 30 participants, 15 carried out the tasks under delayed visual feedback in the order of SR on-condition, off-condition, off-condition, and on-condition. The remaining 15 participants conducted the experimental tasks in the order of SR off-condition, on-condition, on-condition, and off-condition. Comparisons of the delay detection threshold (DDT), steepness of the delay detection probability curves, box and block test (BBT) scores, and nine-hole peg test (NHPT) scores between the SR on- and off-conditions were performed. The DDT under the SR on-condition was significantly shortened compared with the SR off-condition. There was no significant difference between the SR on- and off-conditions for the steepness of the delay detection probability curves, BBT scores, and NHPT scores. SR improved visuomotor temporal integration in healthy young adults, and may therefore improve movement disorders in patients with impaired visuomotor temporal integration. However, because the current results showed that SR did not improve hand motor function under delayed visual feedback, it may not improve motor function when a large distortion of visuomotor temporal integration is present. Further studies are required considering several limitations of the current study, and future clinical trials are necessary to verify the effects of motor training using SR for the treatment of visuomotor temporal integration disorders.

Effect of vibration on postural control and gait of elderly subjects: a systematic review

BACKGROUND AND AIM

Gait and balance disorders are common in the elderly populations, and their prevalence increases with age. This systematic review was performed to summarize the current evidence for subthreshold vibration interventions on postural control and gait in elderly.

METHOD

A review of intervention studies including the following words in the title/abstract: insole, foot and ankle appliances, vibration, noise and elderly related to balance and gait. Databases searched included PubMed, ISI Web of Knowledge, Ovid, Scopus, and Google Scholar. Fifteen articles were selected for final evaluation. The procedure was followed using the preferred reporting items for systematic reviews and meta-analysis method.

RESULTS

There was reduction in center of pressure velocity and displacement especially with eyes closed using vibration in healthy elderly subjects and this effect was greater in elderly faller and patients with more balance deficiency. Vibration programme training increased speed of walking, cadence, step time and length in stroke subjects. The vibratory insoles significantly improved performance on the Timed Up and Go and Functional Reach tests in older people.

CONCLUSION

Vibration was effective on balance improvement in elderly subject especially elderly with more balance deficiency and it can improve gait parameters in patients with greater baseline variability.

Dizziness Handicap Inventory Score Is Highly Correlated With Markers of Gait Disturbance

OBJECTIVE

To evaluate the association between Dizziness Handicap Inventory-Screening version (DHI-S) score and spatiotemporal gait parameters using SoleSound, a newly developed, inexpensive, portable footwear-based gait analysis system.

STUDY DESIGN

Cross-sectional.

PATIENTS

One hundred eighteen patients recruited from otology clinic.

INTERVENTION(S)

Subjects completed the DHI-S survey and four uninterrupted walking laps wearing SoleSound instrumented footwear on a hard, flat surface for 100 m.

MAIN OUTCOME MEASURE(S)

For each subject, mean and coefficient of variation (CV) of stride length, cadence, walking speed, foot-ground clearance, double-support time, swing period, and stance-to-swing were computed by considering 40 strides of steady-state walking within each lap. Linear regression models were employed to study correlations between these variables and DHI-S scores after adjusting for age, sex, and race/ethnicity.

RESULTS

Patients with higher DHI-S score took shorter steps and less steps per minute (-0.017 m and -1.1 steps/min per every four-point increase in DHI-S score, p < 0.05) than patients with a lower DHI-S score, with slower walking speed (-0.025 m/s per every four-point increase in DHI-S score, p < 0.01). Additionally, patients with higher DHI-S scores showed larger variability in all analyzed temporal parameters (+0.1% for CV of cadence, +0.5% for CV of double support period, +0.2% for CV of swing period, and +0.4% for CV of stance-to-swing, per every four-point increase in DHI-S score, p < 0.01).

CONCLUSION

SoleSound was effective in measuring a wide range of gait parameters. Patients' self-perception of vestibular handicap, as assessed with DHI-S, is associated with deterioration in measurable gait parameters independent of age.

Cutaneous sensitivity in unilateral trans-tibial amputees

Aim

To examine tactile sensitivity in the leg and foot sole of below-knee amputees (diabetic n = 3, traumatic n = 1), and healthy control subjects (n = 4), and examine the association between sensation and balance.

Method

Vibration perception threshold (VPT; 3, 40, 250Hz) and monofilaments (MF) were used to examine vibration and light touch sensitivity on the intact limb, residual limb, and homologous locations on controls. A functional reach test was performed to assess functional balance.

Results

Tactile sensitivity was lower for diabetic amputee subjects compared to age matched controls for both VPT and MF; which was expected due to presence of diabetic peripheral neuropathy. In contrast, the traumatic amputee participant showed increased sensitivity for VPT at 40Hz and 250Hz vibration in both the intact and residual limbs compared to controls. Amputees with lower tactile sensitivity had shorter reach distances compared to those with higher sensitivity.

Conclusion

Changes in tactile sensitivity in the residual limb of trans-tibial amputees may have implications for the interaction between the amputee and the prosthetic device. The decreased skin sensitivity observed in the residual limb of subjects with diabetes is of concern as changes in skin sensitivity may be important in 1) identification/prevention of excessive pressure and 2) for functional stability. Interestingly, we saw increased residual limb skin sensitivity in the individual with the traumatic amputation. Although not measured directly in the present study, this increase in tactile sensitivity may be related to cortical reorganisation, which is known to occur following amputation, and would support similar findings observed in upper limb amputees.

Unstable footwear as a speed-dependent noise-based training gear to exercise inverted pendulum motion during walking

Previous research on unstable footwear has suggested that it may induce mechanical noise during walking. The purpose of this study was to explore whether unstable footwear could be considered as a noise-based training gear to exercise body center of mass (CoM) motion during walking. Ground reaction forces were collected among 24 healthy young women walking at speeds between 3 and 6 km h^-1 with control running shoes and unstable rocker-bottom shoes. The external mechanical work, the recovery of mechanical energy of the CoM during and within the step cycles, and the phase shift between potential and kinetic energy curves of the CoM were computed. Our findings support the idea that unstable rocker-bottom footwear could serve as a speed-dependent noise-based training gear to exercise CoM motion during walking. At slow speed, it acts as a stochastic resonance or facilitator that reduces external mechanical work; whereas at brisk speed it acts as a constraint that increases external mechanical work and could mimic a downhill slope.

Effects of White Noise Achilles Tendon Vibration on Quiet Standing and Active Postural Positioning

Applying white noise vibration to the ankle tendons has previously been used to improve passive movement detection and alter postural control, likely by enhancing proprioceptive feedback. The aim of the present study was to determine if similar methods focused on the ankle plantarflexors affect the performance of both quiet standing and an active postural positioning task, in which participants may be more reliant on proprioceptive feedback from actively contracting muscles. Twenty young, healthy participants performed quiet standing trials and active postural positioning trials designed to encourage reliance on plantarflexor proprioception. Performance under normal conditions with no vibration was compared to performance with 8 levels of vibration amplitude applied to the bilateral Achilles tendons. Vibration amplitude was set either as a percentage of sensory threshold (n = 10) or by root-mean-square (RMS) amplitude (n = 10). No vibration amplitude had a significant effect on quiet standing. In contrast, accuracy of the active postural positioning task was significantly (P = .001) improved by vibration with an RMS amplitude of 30 μm. Setting vibration amplitude based on sensory threshold did not significantly affect postural positioning accuracy. The present results demonstrate that appropriate amplitude tendon vibration may hold promise for enhancing the use of proprioceptive feedback during functional active movement.

Efficacy of Stochastic Vestibular Stimulation to Improve Locomotor Performance During Adaptation to Visuomotor and Somatosensory Distortion

Astronauts exposed to microgravity face sensorimotor challenges affecting balance control when readapting to Earth's gravity upon return from spaceflight. Small amounts of electrical noise applied to the vestibular system have been shown to improve balance control during standing and walking under discordant sensory conditions in healthy subjects, likely by enhancing information transfer through the phenomenon of stochastic resonance. The purpose of this study was to test the hypothesis that imperceptible levels of stochastic vestibular stimulation (SVS) could improve short-term adaptation to a locomotor task in a novel sensory discordant environment. Healthy subjects (14 males, 10 females, age = 28.7 ± 5.3 years, height = 167.2 ± 9.6 cm, weight = 71.0 ± 12.8 kg) were tested for perceptual thresholds to sinusoidal currents applied across the mastoids. Subjects were then randomly and blindly assigned to an SVS group receiving a 0–30 Hz Gaussian white noise electrical stimulus at 50% of their perceptual threshold (stim) or a control group receiving zero stimulation during Functional Mobility Tests (FMTs), nine trials of which were done under conditions of visual discordance (wearing up/down vision reversing goggles). Time to complete the course (TCC) was used to test the effect of SVS between the two groups across the trials. Adaptation rates from the normalized TCCs were also compared utilizing exponent values of power fit trendline equations. A one-tailed independent-samples t-test indicated these adaptation rates were significantly faster in the stim group (n = 12) than the control (n = 12) group [t_(16.18) = 2.00, p = 0.031]. When a secondary analysis was performed comparing “responders” (subjects who showed faster adaptation rates) of the stim (n = 7) group to the control group (n = 12), independent-samples t-tests revealed significantly faster trial times for the last five trials with goggles in the stim group “responders” than the controls. The data suggests that SVS may be capable of improving short-term adaptation to a locomotion task done under sensory discordance in a group of responsive subjects.

Effect of footwear on standing balance in healthy young adult males

OBJECTIVE

The present study aimed to evaluate the effect of footwear on standing balance in healthy young adult males.

METHODS

Thirty healthy male participants aged 20-30 years were tested for standing balance on the Balance Master on three occasions, including wearing a sandal, standard shoe, or no footwear (barefoot). The tests of postural stability include; "Modified Clinical Test of Sensory Interaction on Balance" (mCTSIB), "Unilateral Stance" (US), and the "Limits of Stability" (LOS). The balance scores (mCTSIB, US, and LOS) was analyzed.

RESULTS

There was a significant effect between footwear conditions for mCTIB with eye closed on a firm surface (p=0.002). There was a significant effect between footwear conditions for the US with eye open and closed (p⟨0.05). There was a significant effect between footwear conditions for LOS reaction time during forward movement (p=0.02). Similarly, there was a significant effect between footwear conditions for LOS reaction time during left side movement (p=0.01).

CONCLUSIONS

Wearing sandals compared to bare feet significantly increased postural sway and reduced stability in healthy young adult males. However, wearing a standard shoe compared to bare feet did not significantly affect balance scores in standing.

The effect of flat and textured insoles on the balance of primary care elderly people: a randomized controlled clinical trial

BACKGROUND

Aging is associated with reduced postural stability and increased fall risk. Foot orthoses have been reported as an adjuvant intervention to improve balance by stimulating foot plantar mechanical receptors and thus increasing somatosensory input.

PURPOSE

The aim of this study is to evaluate the effect of flat and textured insoles on the balance of primary care elderly people.

DESIGN

Prospective, parallel, randomized, and single-blind trial.

METHODS

A total of 100 subjects from a primary care unit, aged ≥65 years, were randomly assigned to intervention groups with flat insoles (n=33), textured insoles (n=33), or control group (n=34) without insoles. The Berg Balance Scale and the Timed Up and Go test were assessed at baseline and after 4 weeks.

RESULTS

Improvements in the Berg Balance Scale and the Timed Up and Go test were noted only in intervention groups with insoles but not in control group. No significant difference was found between flat and textured insoles. Minor adverse effects were noted only in the group with textured insoles.

CONCLUSION

The results suggest that foot orthoses (both flat and textured insoles) are effective in improving balance in primary care elderly people. They may represent a low-cost and high-availability adjuvant strategy to improve balance and prevent falls in this population.

Low-power transcutaneous current stimulator for wearable applications

BACKGROUND

Peripheral neuropathic desensitization associated with aging, diabetes, alcoholism and HIV/AIDS, affects tens of millions of people worldwide, and there is little or no treatment available to improve sensory function. Recent studies that apply imperceptible continuous vibration or electrical stimulation have shown promise in improving sensitivity in both diseased and healthy participants. This class of interventions only has an effect during application, necessitating the design of a wearable device for everyday use. We present a circuit that allows for a low-power, low-cost and small form factor implementation of a current stimulator for the continuous application of subthreshold currents.

RESULTS

This circuit acts as a voltage-to-current converter and has been tested to drive + 1 to - 1 mA into a 60 k[Formula: see text] load from DC to 1 kHz. Driving a 60 k[Formula: see text] load with a 2 mA peak-to-peak 1 kHz sinusoid, the circuit draws less than 21 mA from a 9 V source. The minimum operating current of the circuit is less than 12 mA. Voltage compliance is ± 60 V with just 1.02 mA drawn by the high voltage current drive circuitry. The circuit was implemented as a compact 46 mm × 21 mm two-layer PCB highlighting its potential for use in a body-worn device.

CONCLUSIONS

No design to the best of our knowledge presents comparably low quiescent power with such high voltage compliance. This makes the design uniquely appropriate for low-power transcutaneous current stimulation in wearable applications. Further development of driving and instrumentation circuitry is recommended.

The firing characteristics of foot sole cutaneous mechanoreceptor afferents in response to vibration stimuli

Single unit microneurography was used to record the firing characteristics of the four classes of foot sole cutaneous afferents [fast and slowly adapting type I and II (FAI, FAII, SAI, and SAII)] in response to sinusoidal vibratory stimuli. Frequency (3-250 Hz) and amplitude (0.001-2 mm) combinations were applied to afferent receptive fields through a 6-mm diameter probe. The impulses per cycle, defined as the number of action potentials evoked per vibration sine wave, were measured over 1 s of vibration at each frequency-amplitude combination tested. Afferent entrainment threshold (lowest amplitude at which an afferent could entrain 1:1 to the vibration frequency) and afferent firing threshold (minimum amplitude for which impulses per cycle was greater than zero) were then obtained for each frequency. Increases in vibration frequency are generally associated with decreases in expected impulses per cycle (P < 0.001), but each foot sole afferent class appears uniquely tuned to vibration stimuli. FAII afferents tended to have the lowest entrainment and firing thresholds (P < 0.001 for both); however, these afferents seem to be sensitive across frequency. In contrast to FAII afferents, SAI and SAII afferents tended to demonstrate optimal entrainment to frequencies below 20 Hz and FAI afferents faithfully encoded frequencies between 8 and 60 Hz. Contrary to the selective activation of distinct afferent classes in the hand, application of class-specific frequencies in the foot sole is confounded due to the high sensitivity of FAII afferents. These findings may aid in the development of sensorimotor control models or the design of balance enhancement interventions.NEW & NOTEWORTHY Our work provides a mechanistic look at the capacity of foot sole cutaneous afferents to respond to vibration of varying frequency and amplitude. We found that foot sole afferent classes are uniquely tuned to vibration stimuli; however, unlike in the hand, they cannot be independently activated by class-specific frequencies. Viewing the foot sole as a sensory structure, the present findings may aid in the refinement of sensorimotor control models and design of balance enhancement interventions.

Design and evaluation of vibratory shoe on balance control for elderly subjects: technical note

BACKGROUND AND AIM

Aging often results in a decline in somatosensory function, and such changes are associated with diminished motor performance. Input noise can enhance sensory and motor function through a mechanism known as stochastic resonance (SR). This paper describes the development and testing of a new vibrating shoe to possibly assist the elderly patients in controlling their balance and decreasing their falling risks.

TECHNIQUE

The new vibrating shoe was evaluated to ascertain its ability to generate appropriate random and nonlinear vibrations. The vibratory shoe performance in two young subjects with decreased foot sensation and two elderly subjects in different static and dynamic balance situations was also evaluated. The postural control, expressed by the stability index (SI), was significantly affected by SR in the older subjects.

DISCUSSION

The vibrating motors could be recommended as a suitable solution for dynamic balance situations. Moreover, the new vibrating shoe could improve the age-related balance impairments in elderly subjects with balance deficiencies and others with impaired foot sensations. Implications for rehabilitations Older adults exhibited decreased postural stability. Noise signal improves sensation and proprioception in older people. New shoe with vibrating motors can operate in different dynamic situations.

Tactile stimuli affect long-range correlations of stride interval and stride length differently during walking

Sensory feedback below the sole of the foot using sub-threshold mechanical noise significantly reduced postural sway in patients with diabetes and stroke. However, the effects of tactile parameters on walking are still elusive. Specifically, the effects of such parameters on human gait variability need to be studied because of possible rehabilitation outcomes in terms of bringing improvement in temporal and spatial gait parameters. The purpose of this study was to investigate whether different frequency and amplitude combinations of vibro-tactile stimulation of feet would affect stride-to-stride variability in healthy young adults. Ten healthy subjects walked on a treadmill at self-selected pace while wearing customized insoles fitted with tactors that vibrated at selected frequencies and amplitudes. The results show that the frequency manipulations of tactile stimulation altered the long-range correlations (LRCs) in stride length while amplitude manipulations affected the LRCs in stride interval without having any effect on the amount of gait variability. Our findings suggest that independent neural mechanisms may be responsible for coordinating LRCs of gait parameters in the spatial and temporal domains.

The clinical and biomechanical effects of subthreshold random noise on the plantar surface of the foot in diabetic patients and elder people: A systematic review

BACKGROUND

Central nervous system receives information from foot mechanoreceptors in order to control balance and perform movement tasks. Subthreshold random noise seems to improve sensitivity of the cutaneous mechanoreceptor.

OBJECTIVES

The purpose of this study was to systematically review published evidence conducted to evaluate the clinical and biomechanical effects of subthreshold random noise on the plantar surface of the foot in diabetic patients and elder people.

STUDY DESIGN

Systematic review.

METHODS

A literature search was performed in PubMed, Scopus, ScienceDirect, Web of Knowledge, CINAHL, and EMBASE databases based on population, intervention, comparison, outcomes, and study method. Quality of studies was assessed using the methodological quality assessment tool, using Physiotherapy Evidence Database scale.

RESULTS

In all, 11 studies were selected for final evaluation based on inclusion criteria. Five studies evaluated the effects of subthreshold random noise in diabetic patients and six in elder people. In seven studies, biomechanical (balance and gait parameters) effects and in four studies clinical (pressure and vibration sensations) effects of subthreshold random noise were investigated. All reviewed studies were scored fair (2) to good (9) quality in terms of methodological quality assessment using Physiotherapy Evidence Database scale.

CONCLUSION

The results indicated that subthreshold random noise improves balance and sensation in diabetic patients and elder people. Also gait variables can be improved in elder people with subthreshold random noise. However, further well-designed studies are needed.

CLINICAL RELEVANCE

The previous studies reported that subthreshold random noise may improve gait, balance, and sensation, but more studies are needed to evaluate the long-term effect of subthreshold random noise in shoe or insole for daily living tasks in diabetic patients and elder people.

Effects of foot and ankle devices on balance, gait and falls in adults with sensory perception loss: a systematic review

BACKGROUND

Foot and ankle devices are being developed as a method of preventing people with sensory perception loss sustaining a fall. Such devices are believed to work by reducing the likelihood of a fall by improving the balance and gait of the user.

OBJECTIVES

The objective of the review was to evaluate the effectiveness of foot and ankle devices for the prevention of falls and the improvement of balance and gait in adults with sensory perception loss.

INCLUSION CRITERIA TYPES OF PARTICIPANTS

Participants were community-dwelling adults with bilateral pathological sensory perception loss.

TYPES OF INTERVENTION(S)/PHENOMENA OF INTEREST

The current review evaluated any foot or ankle device, including but not restricted to, all types of footwear (therapeutic and retail), insoles (customized and prefabricated) and ankle-foot orthoses (AFOs).

TYPES OF STUDIES

In the absence of randomized controlled trials (RCT), the review considered experimental and epidemiological study designs, except case series, individual case reports and descriptive cross-sectional studies.

OUTCOMES

The primary outcome was number of falls. Secondary outcome measures were clinical or laboratory measures of balance or gait.

SEARCH STRATEGY

A search for published and unpublished literature from inception to March 2015 written in the English language was conducted across a number of major electronic databases. A three-step search strategy was developed using MeSH terminology and keywords to ensure all that relevant materials are captured.

METHODOLOGICAL QUALITY

Methodological quality of included studies was assessed by two reviewers, who appraised each study independently, using standardized Joanna Briggs Institute (JBI) critical appraisal tools.

DATA EXTRACTION

Quantitative data were extracted from the studies that were identified as meeting the criteria for methodological quality using the standardized JBI data extraction tools.

DATA SYNTHESIS

Due to the heterogeneity of populations, interventions and outcome measures, meta-analyses were not possible and results are presented in narrative form.

RESULTS

Nine trials (from 10 papers) involving 238 participants, (14 with multiple sclerosis and 16 with idiopathic peripheral neuropathy, 150 with diabetic neuropathy) and 58 controls were included in the review. No study reported falls as an outcome measure. The results of the included studies found that in people with sensory perception loss, postural sway improved with vibrating insoles and AFO, altering the softness and texture of the top cover had no effect on postural sway, wearing footwear over long distances or AFOs improved step-to-step consistency, and no foot and ankle device was reported to have a negative effect on the balance or gait of people with sensory perception loss. The methodological quality of the included studies was poor. No study used a randomized controlled trial (RCT) methodology. No study incorporated a follow-up period or tested the intervention within the context of the intended clinical environment.

CONCLUSION

There is limited evidence to suggest that footwear and insole devices can artificially alter postural stability and may reduce the step-to-step variability in adults with sensory perception loss. Varying the material properties of an insole does not notably affect static balance or gait.

Aging, the Central Nervous System, and Mobility in Older Adults: Interventions

BACKGROUND

Research suggests that the central nervous system (CNS) and mobility are closely linked. CNS-mediated mobility impairment may represent a potentially new and prevalent syndrome within the older adult populations. Interventions targeting this group may have the potential to improve mobility and cognition and prevent disability.

METHODS

In 2012, the Gerontological Society of America (GSA) and the National Institute on Aging (NIA) sponsored a 3-year conference workshop series, "Aging, the CNS, and Mobility." The goal of this third and final conference was to (i) report on the state of the science of interventions targeting CNS-mediated mobility impairment among community-dwelling older adults and (ii) partnering with the NIA, explore the future of research and intervention design focused on a potentially novel aging syndrome.

RESULTS

Evidence was presented in five main intervention areas: (i) pharmacology and diet; (ii) exercise; (iii) electrical stimulation; (iv) sensory stimulation/deprivation; and (v) a combined category of multimodal interventions. Workshop participants identified important gaps in knowledge and key recommendations for future interventions related to recruitment and sample selection, intervention design, and methods to measure effectiveness.

CONCLUSIONS

In order to develop effective preventive interventions for this prevalent syndrome, multidisciplinary teams are essential particularly because of the complex nature of the syndrome. Additionally, integrating innovative methods into the design of interventions may help researchers better measure complex mechanisms, and finally, the value of understanding the link between the CNS and mobility should be conveyed to researchers across disciplines in order to incorporate cognitive and mobility measurements into study protocols.

Use of an Enactive Insole for Reducing the Risk of Falling on Different Types of Soil Using Vibrotactile Cueing for the Elderly

Background

Our daily activities imply displacements on various types of soil. For persons with gait disorder or losing functional autonomy, walking on some types of soil could be challenging because of the risk of falling it represents.

Methods

In this paper, we present, in a first part, the use of an enactive shoe for an automatic differentiation of several types of soil. In a second part, using a second improved prototype (an enactive insole), twelve participants with Parkinson’s disease (PD) and nine age-matched controls have performed the Timed Up and Go (TUG) test on six types of soil with and without cueing. The frequency of the cueing was set at 10% above the cadence computed at the lower risk of falling (walking over the concrete). Depending on the cadence computed at the lower risk, the enactive insole activates a vibrotactile cueing aiming to improve gait and balance control. Finally, a risk index is computed using gait parameters in relation to given type of soil.

Results

The frequency analysis of the heel strike vibration allows the differentiation of various types of soil. The risk computed is associated to an appropriate rhythmic cueing in order to improve balance and gait impairment. The results show that a vibrotactile cueing could help to reduce the risk of falling.

Conclusions

Firstly, this paper demonstrates the feasibility of reducing the risk of falling while walking on different types of soil using vibrotactile cueing. We found a significant difference and a significant decrease in the computed risks of falling for most of types of soil especially for deformable soils which can lead to fall. Secondly, heel strike provides an approximation of the impulse response of the soil that can be analyzed with time and frequency-domain modeling. From these analyses, an index is computed enabling differentiation the types of soil.

Do Aging and Tactile Noise Stimulation Affect Responses to Support Surface Translations in Healthy Adults?

Appropriate neuromuscular responses to support surface perturbations are crucial to prevent falls, but aging-related anatomical and physiological changes affect the appropriateness and efficiency of such responses. Low-level noise application to sensory receptors has shown to be effective for postural improvement in a variety of different balance tasks, but it is unknown whether this intervention may have value for improvement of corrective postural responses. Ten healthy younger and ten healthy older adults were exposed to sudden backward translations of the support surface. Low-level noise (mechanical vibration) to the foot soles was added during random trials and temporal (response latency) and spatial characteristics (maximum center-of-pressure excursion and anterior-posterior path length) of postural responses were assessed. Mixed-model ANOVA was applied for analysis of postural response differences based on age and vibration condition. Age affected postural response characteristics, but older adults were well able to maintain balance when exposed to a postural perturbation. Low-level noise application did not affect any postural outcomes. Healthy aging affects some specific measures of postural stability, and in high-functioning older individuals, a low-level noise intervention may not be valuable. More research is needed to investigate if recurring fallers and neuropathy patients could benefit from the intervention in postural perturbation tasks.

Sub-sensory vibratory noise augments the physiologic complexity of postural control in older adults

Background

Postural control requires numerous inputs interacting across multiple temporospatial scales. This organization, evidenced by the “complexity” contained within standing postural sway fluctuations, enables diverse system functionality. Age-related reduction of foot-sole somatosensation reduces standing postural sway complexity and diminishes the functionality of the postural control system. Sub-sensory vibrations applied to the foot soles reduce the speed and magnitude of sway and improve mobility in older adults. We thus hypothesized that these vibration-induced improvements to the functionality of the postural control system are associated with an increase in the standing postural sway complexity.

Method

Twelve healthy older adults aged 74 ± 8 years completed three visits to test the effects of foot sole vibrations at 0 % (i.e., no vibration), 70 and 85 % of the sensory threshold. Postural sway was assessed during eyes-open and eyes-closed standing. The complexity of sway time-series was quantified using multiscale entropy. The timed up-and-go (TUG) was completed to assess mobility.

Results

When standing without vibration, participants with lower foot sole vibratory thresholds (better sensation) had greater mediolateral (ML) sway complexity (r² = 0.49, p < 0.001), and those with greater ML sway complexity had faster TUG times (better mobility) (r² = 0.38, p < 0.001). Foot sole vibrations at 70 and 85 % of sensory threshold increased ML sway complexity during eyes-open and eyes-closed standing (p < 0.0001). Importantly, these vibration-induced increases in complexity correlated with improvements in the TUG test of mobility (r² = 0.15 ~ 0.42, p < 0.001 ~ 0.03).

Conclusions

Sub-sensory foot sole vibrations augment the postural control system functionality and such beneficial effects are reflected in an increase in the physiologic complexity of standing postural sway dynamics.

The effects of prolonged wear of textured shoe insoles on gait, foot sensation and proprioception in people with multiple sclerosis: study protocol for a randomised controlled trial

BACKGROUND

Many people with multiple sclerosis experience problems with walking, which can make daily activities difficult and often leads to falls. Foot sensation plays an important role in keeping the body balanced whilst walking; however, people with multiple sclerosis often have poor sensation on the soles of their feet. Wearing a specially designed shoe insole, which enhances plantar sensory information, could help people with multiple sclerosis to walk better. This study will explore whether long-term wear of a textured insole can improve walking in people with multiple sclerosis.

METHODS

A prospective randomised controlled trial with two parallel groups will be conducted aiming to recruit 176 people with multiple sclerosis living in the community (Brisbane, Australia). Adults with a clinical diagnosis of multiple sclerosis, Disease Steps score 1-4, who are ambulant over 100 m and who meet specific inclusion criteria will be recruited. Participants will be randomised to a smooth control insole (n = 88) or textured insole (n = 88) group. The allocated insole will be worn for 12-weeks within participants' own footwear, with self-report wear diaries and falls calendars being completed over this period. Blinded assessors will conduct two baseline assessments and one post-intervention assessment. Gait tasks will be completed barefoot, wearing standardised footwear only, and wearing standardised footwear with smooth and textured insoles. The primary outcome measure will be mediolateral base of support when walking over even and uneven surfaces. Secondary measures include spatiotemporal gait parameters (stride length, stride time variability, double-limb support time, velocity), gait kinematics (hip, knee, and ankle joint angles, toe clearance, trunk inclination, arm swing, mediolateral pelvis/head displacement), foot sensation (light touch-pressure, vibration, two-point discrimination) and proprioception (ankle joint position sense). Group allocation will be concealed and all analyses will be based on an intention-to-treat principle.

DISCUSSION

This study will explore the effects of wearing textured insoles over 12-weeks on gait, foot sensation and proprioception in people with multiple sclerosis. The study has the potential to identify a new, evidence-based footwear intervention which has the capacity to enhance mobility and independent living in people with multiple sclerosis.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry ACTRN12615000421538 . Registered 4 May 2015.

Associations between Tactile Sensory Threshold and Postural Performance and Effects of Healthy Aging and Subthreshold Vibrotactile Stimulation on Postural Outcomes in a Simple Dual Task

Specific activities that require concurrent processing of postural and cognitive tasks may increase the risk for falls in older adults. We investigated whether peripheral receptor sensitivity was associated with postural performance in a dual-task and whether an intervention in form of subthreshold vibration could affect performance. Ten younger (age: 20–35 years) and ten older adults (70–85 years) performed repeated auditory-verbal 1-back tasks while standing quietly on a force platform. Foot sole vibration was randomly added during several trials. Several postural control and performance measures were assessed and statistically analyzed (significance set to α-levels of .05). There were moderate correlations between peripheral sensitivity and several postural performance and control measures (r = .45 to .59). Several postural performance measures differed significantly between older and younger adults (p < 0.05); addition of vibration did not affect outcome measures. Aging affects healthy older adults' performance in dual-tasks, and peripheral sensitivity may be a contributor to the observed differences. A vibration intervention may only be useful when there are more severe impairments of the sensorimotor system. Hence, future research regarding the efficacy of sensorimotor interventions in the form of vibrotactile stimulation should focus on older adults whose balance is significantly affected.