Reduced plantar sensation causes a cautious walking pattern

An MRI-Compatible System for Characterizing Supraspinal Processing of Walking-Related Foot-Sole Somatosensory Stimulation

Foot soles are the only part in direct contact with the ground during walking. The mechanoreceptors on foot soles continuously obtain somatosensory information (e.g., ground reaction forces) that is delivered to spinal and supraspinal networks. The timely and accurate supraspinal processing of such information, which can be captured by the activation of the supraspinal regions, is critical to the regulation of walking. However, little is known about supraspinal somatosensory processing related to walking. Characterizing the supraspinal response to walking-related somatosensory inputs using MRI is challenging, because individuals are required to stay motionless during MRI scan. We thus developed a stimulation system that simulates the amplitude and timing of foot-sole pressure changes experienced during each step of overground walking, without inducing significant head motion. In the study to examine its validity and reliability of simulation, seven younger adults completed two trials of eight-meter walking. The temporal changes of foot-sole pressure of each step during walking were recorded using a pressure insole and used to program the motion of the system. The results indicated high validity and reliability of the stimulation (rho $= 0.94\sim 0.98$ , p<0.0001). Phantom imaging test revealed that the signal-to-noise ratio of the MR image when the system working was similar to when the system was off, suggesting excellent MRI compatibility. Finally, block-designed test indicated that, compared to rest, multiple supraspinal regions (e.g., postcentral gyrus) were activated (p<0.005) by foot-sole stimulation. This MRI-compatible system provides a novel approach to characterizing the supraspinal sensorimotor control of walking via MRI.

Skin tactile perception is associated with longitudinal gait performance in middle-aged and older Japanese community dwellers

BACKGROUND

Skin tactile perception may indicate frailty in older adults. Although gait performance is crucial for diagnosing frailty, its association with skin tactile perception has not yet been explored.

OBJECTIVES

To examine the association between skin tactile perception and changes in step length, cadence, and gait speed in middle-aged and older adults.

DESIGN

A longitudinal study (mean follow-up: 10.8 years) SETTING: Community-based survey PARTICIPANTS: A total of 1,403 middle-aged and older adults (aged 40-79 years, 53.6 % men) from the National Institute for Longevity Sciences-Longitudinal Study of Aging were included in this study. These participants completed the baseline survey (1997-2000) and at least two follow-up surveys (2000-2012), had no history of cerebrovascular disease, rheumatoid arthritis, or Parkinson's disease, and had complete data with no outliers in skin tactile perception measurements.

MEASUREMENTS

Skin tactile perception was assessed using a two-point discrimination test. Step length (cm), cadence (steps/min), and gait speed (m/min) were evaluated on an 11-m walkway at a usual speed.

RESULTS

The mean age of participants was 56.4 years. After full adjustment, mixed-effects models with splines revealed that the association between skin tactile perception and gait parameters varied with age. In adults aged 60 and above, we observed non-linear relationships between skin tactile perception and gait parameters. A consistent inflection point around 10 mm in tactile perception was identified across different age groups and gait parameters.

CONCLUSIONS

Among community-dwelling middle-aged and older Japanese adults, skin tactile perception was associated with changes in gait parameters, particularly in those aged 60 and above. The 10-mm threshold in tactile perception may serve as a critical indicator for predicting changes in gait performance. Skin tactile perception tests may prove clinically useful for screening patients at elevated risk of impaired gait performance.

Long-term performance and stability of implanted neural interfaces in individuals with lower limb loss

Objective.High-density nerve cuffs have been successfully utilized to restore somatosensation in individuals with lower-limb loss by interfacing directly with the peripheral nervous system. Elicited sensations via these devices have improved various functional outcomes, including standing balance, walking symmetry, and navigating complex terrains. Deploying neural interfaces in the lower limbs of individuals with limb loss presents unique challenges, particularly due to repetitive muscle contractions and the natural range of motion in the knee and hip joints for transtibial and transfemoral amputees, respectively. This study characterizes the long-term performance of these peripheral nerve interfaces, which is crucial for informing design modifications to optimize functionality.Approach.We evaluated the longitudinal performance of 16-contact nerve cuffs and their associated components implanted in four participants with unilateral transtibial limb loss over five years. Key outcome measures included charge density at sensory thresholds and electrical impedance.Main results.Out of 158 channels (i.e. individual contacts within the nerve cuffs and their corresponding leads), 63% were consistently responsive, 33% were partially responsive, and 4% were non-responsive. Smaller connector assemblies and increased lead length near the cuffs significantly enhanced performance, with the final two participants demonstrating notably improved responses where 77% and 96% of channels were consistently responsive, respectively, compared to 50% and 6% in the first two participants.Significance.Overall, the implanted nerve cuffs showed robust stability in the residual limbs of highly active individuals with limb loss. Furthermore, employing strategies to reduce stress on transition points in the components significantly improved overall system performance.

Enhanced Foot Proprioception Through 3-Minute Walking Bouts with Ultra-Minimalist Shoes on Surfaces That Mimic Highly Rugged Natural Terrains

The use of minimalist shoes can lead to enhanced foot somatosensory activation and postural stability but can also increase the incidence of overuse injuries during high-impact or prolonged activities. Therefore, it appears useful to explore new strategies that employ minimalist shoes to effectively facilitate the somatosensory activation of the foot while minimizing acute and cumulative joint stress and risk of injury. To this purpose, this study introduces a novel exercise paradigm: walking for three minutes in ultra-minimalist shoes on artificial flat surfaces designed to mimic highly rugged natural terrains. The activity of foot muscles and lumbar multifidus, pain perception level, and stabilometric parameters were recorded and analyzed to characterize the novel exercise, comparing it to walking barefoot or in conventional shoes on the same rugged surface. Compared to being barefoot, ultra-minimalist shoes effectively filter nociceptive stimuli from the rugged surface, while compared to conventional shoes, they enhance the somatosensory input supporting static stability. Walking with ultra-minimalist and conventional shoes yielded higher gastrocnemius activity and lower tibialis anterior and multifidus activity compared to barefoot walking. This study highlights a practical and safe framework for enhancing foot somatosensory activation and postural stability. The new intervention is suitable for people of all ages, requires minimal time commitment, and can be performed in controlled environments such as homes, gyms, and healthcare facilities.

Normative Extensor Hallucis Brevis Muscle Activity During Locomotion Following the Development of a Novel Ultrasound-Guided Fine-Wire Electromyography Protocol

Fine-wire electromyography (EMG) is a traditional laboratory technique to estimate muscle activity of the small foot muscles, however, recordings have not been reported from extensor hallucis brevis (EHB). As an extensor of the great toe, EHB is an important muscle when studying physiological changes associated with foot pathologies such as hallux valgus. The purpose of this study was to develop an ultrasound-guided fine-wire EMG protocol to record EHB muscle activity and report normative EMG profiles of healthy young adults during locomotion. Sixteen asymptomatic young adults completed 20 walking trials at a self-selected velocity. Ensemble averages were calculated from the time normalized linear envelopes and represented from 0% to 100% of the single stance phase of gait. EHB muscle bursts were observed between 0% and 20% of the stance phase of gait in all participants. A second burst of EMG was observed between 80% and 100% of stance in 50% of the participants. This study introduces a novel ultrasound-guided EMG protocol and normative data from EHB recordings suggest a synergistic role to anterior compartment musculature at contact. These results provide preliminary insights into understanding the functional role of EHB and may help elucidate the biomechanical factors exacerbating the progression of hallux pathologies.

The suppression of lower leg electromyography when walking in textured foot orthoses

Previous research exploring the effects of tactile feedback in standing balance protocols may have generated results that misrepresent the modulatory capabilities of cutaneous afference on generating motor output responses. The neurosensory mechanism of textured foot orthoses to maximize the activation of cutaneous mechanoreceptors is through repetitive foot sole skin indentation. Thus, the purpose of this experimental protocol was to investigate muscular activity amplitude changes during the stance phase of gait, specifically when walking on level ground and when stepping onto a raised wedge, and while wearing textured foot orthoses compared to orthoses without texture. Twenty-one healthy young adults were fit to a standardized neutral running shoe and completed five level and wedged walking trials wearing both orthoses. Kinematic, kinetic and electromyography (EMG) data were recorded from eight lower limb muscles. The results of this study revealed EMG suppression of lower leg musculature during stance when walking in textured foot orthoses, and this was most pronounced when lower leg musculature is typically most active. The addition of texture in foot orthoses design, spanning the entire length of the foot sole, appears to be a clear mechanism to modulate neurosensory feedback with intent to suppress EMG of shank musculature during gait.

Behavioral adjustment of C. elegans to mechanosensory loss requires intact mechanosensory neurons

Sensory neurons specialize in detecting and signaling the presence of diverse environmental stimuli. Neuronal injury or disease may undermine such signaling, diminishing the availability of crucial information. Can animals distinguish between a stimulus not being present and the inability to sense that stimulus in the first place? To address this question, we studied Caenorhabditis elegans nematode worms that lack gentle body touch sensation due to genetic mechanoreceptor dysfunction. We previously showed that worms can compensate for the loss of touch by enhancing their sense of smell, via an FLP-20 neuropeptide pathway. Here, we find that touch-deficient worms exhibit, in addition to sensory compensation, also cautious-like behavior, as if preemptively avoiding potential undetectable hazards. Intriguingly, these behavioral adjustments are abolished when the touch neurons are removed, suggesting that touch neurons are required for signaling the unavailability of touch information, in addition to their conventional role of signaling touch stimulation. Furthermore, we found that the ASE taste neurons, which similarly to the touch neurons, express the FLP-20 neuropeptide, exhibit altered FLP-20 expression levels in a touch-dependent manner, thus cooperating with the touch circuit. These results imply a novel form of neuronal signaling that enables C. elegans to distinguish between lack of touch stimulation and loss of touch sensation, producing adaptive behavioral adjustments that could overcome the inability to detect potential threats.

Mechanoreceptor sensory feedback is impaired by pressure induced cutaneous ischemia on the human foot sole and can predict cutaneous microvascular reactivity

Introduction

The foot sole endures high magnitudes of pressure for sustained periods which results in transient but habitual cutaneous ischemia. Upon unloading, microvascular reactivity in cutaneous capillaries generates an influx of blood flow (PORH: post-occlusive reactive hyperemia). Whether pressure induced cutaneous ischemia from loading the foot sole impacts mechanoreceptor sensitivity remains unknown.

Methods

Pressure induced ischemia was attained using a custom-built-loading device that applied load to the whole right foot sole at 2 magnitudes (15 or 50% body weight), for 2 durations (2 or 10 minutes) in thirteen seated participants. Mechanoreceptor sensitivity was assessed using Semmes-Weinstein monofilaments over the third metatarsal (3MT), medial arch (MA), and heel. Perceptual thresholds (PT) were determined for each site prior to loading and then applied repeatedly to a metronome to establish the time course to return to PT upon unload, defined as PT recovery time. Microvascular flux was recorded from an in-line laser speckle contrast imager (FLPI-2, Moor Instruments Inc.) to establish PORH peak and recovery rates at each site.

Results

PT recovery and PORH recovery rate were most influenced at the heel and by load duration rather than load magnitude. PT recovery time at the heel was significantly longer with 10 minutes of loading, regardless of magnitude. Heel PORH recovery rate was significantly slower with 10minutes of loading. The 3MT PT recovery time was only longer after 10 minutes of loading at 50% body weight. Microvascular reactivity or sensitivity was not influenced with loading at the MA. A simple linear regression found that PORH recovery rate could predict PT recovery time at the heel (R2=0.184, p<0.001).

Conclusion

In populations with degraded sensory feedback, such as diabetic neuropathy, the risk for ulcer development is heightened. Our work demonstrated that prolonged loading in healthy individuals can impair skin sensitivity, which highlights the risks of prolonged loading and is likely exacerbated in diabetes. Understanding the direct association between sensory function and microvascular reactivity in age and diabetes related nerve damage, could help detect early progressions of neuropathy and mitigate ulcer development.

Differences in kinetic factors affecting gait speed between lesion sides in patients with stroke

The differences in kinetic mechanisms of decreased gait speed across brain lesion sides have not been elucidated, including the arrangement of motor modules reflected by kinetic interjoint coordination. The purpose of this study was to elucidate the differences in the kinetic factors of slow gait speed in patients with stroke on the lesion sides. A three-dimensional motion analysis system was employed to assess joint moment in the lower limb and representative gait parameters in 32 patients with right hemisphere brain damage (RHD) and 38 patients with left hemisphere brain damage (LHD) following stroke as well as 20 healthy controls. Motor module composition and timing were determined using principal component analysis based on the three joint moments in the lower limb in the stance phase, which were the variances accounted for principal components (PCs) and the peak timing in the time series of PCs. A stepwise multiple linear regression analysis was performed to identify the most significant joint moment and PC-associated parameter in explaining gait speed. A negligible difference was observed in age, weight, height, and gait speed among patients with RHD and LHD and controls. The following factors contributed to gait speed: in patients with RHD, larger ankle plantarflexion moment on the paretic (p = 0.001) and nonparetic (p = 0.002) sides and ankle dorsiflexion moment on the nonparetic side (p = 0.004); in patients with LHD, larger ankle plantarflexion moment (p < 0.001) and delayed peak timing of the first PC (p = 0.012) on the paretic side as well as ankle dorsiflexion moment on the nonparetic side (p < 0.001); in the controls, delayed peak timing of the first PC (p = 0.002) on the right side and larger ankle dorsiflexion moment (p = 0.001) as well as larger hip flexion moment on the left side (p = 0.023). The findings suggest that the kinetic mechanisms of gait speed may differ among patients with RHD following patients with stroke with LHD, and controls.

The topographical attenuation of cutaneous input is modulated at the ankle joint during gait

The attenuation of sensory inputs via various methods has been demonstrated to impair balance control and alter locomotor behavior during human walking; however, the effects of attenuating foot sole sensation under distinct areas of the foot sole on lower extremity motor output remains poorly understood. Thus, the purpose of this study was to attenuate cutaneous feedback via regional hypothermia under five different areas of the foot sole and investigate the resultant modulation of kinematic and muscle activity during level walking. Electromyography from eight lower leg muscles, kinematics, and location of center of pressure was recorded from 48 healthy young adults completing walking trials with normal and reduced cutaneous sensation from bilateral foot soles. The results of this study highlight the modulatory response of the tibialis anterior in terminal stance (propulsion and toe-off) and medial gastrocnemius muscle throughout the entire stance phase of gait. The topographical organization of foot sole skin in response to the attenuation of cutaneous feedback from different areas of the foot sole significantly modified locomotor activity. Furthermore, the locomotor response to cutaneous attenuation under the same regions that we previously facilitated with tactile feedback do not oppose each other, suggesting different physiological changes to foot sole skin generate unique gait behaviors.

Heating the skin on the foot sole enhances cutaneous reflexes in the lower limb

Cutaneous input is important in postural control and balance. Aging and diabetes impair skin sensitivity and motor control. Heat application can improve skin sensation, but its influence on motor control remains unknown. This study investigated the effects of heating the skin of the foot sole on lower limb cutaneous reflexes. Reflexes were evoked in the tibialis anterior muscle of 20 young, healthy adults before and after heating the foot sole to a maximum of 42°C. While holding a 15% maximum root mean square EMG generated during maximum isometric dorsiflexion, a filtered white noise (0-50 Hz) vibration at 10 times the perceptual threshold was applied to the heel to stimulate cutaneous mechanoreceptors. Reflexes were analyzed in both the time (cumulant density) and frequency (coherence, gain) domains. Heat increased foot skin temperature ∼15.4°C (P < 0.001). Cumulant density peak to peak amplitude significantly increased by 44% after heating (P = 0.01) while latencies did not vary (P = 0.46). Coherence and gain were significantly greater in the 30- to 40-Hz range following heating (P = 0.048; P = 0.02). Heating significantly enhances lower limb cutaneous reflexes. This may be due to the increased ability of cutaneous mechanoreceptors to encode in the 30- to 40-Hz range.NEW & NOTEWORTHY Cutaneous input is a known modulator of muscle activity. Targeting skin to intentionally enhance motor output has received little attention. We explored local skin heating to enhance skin sensitivity and found a significant increase in the amplitude, coherence, and gain of cutaneous reflexes in the tibialis anterior. Our current findings provide the first support for the use of heat as a viable and easily integrated modality in rehabilitation technology to improve balance and postural control.

Impaired foot vibration sensitivity is related to altered plantar pressures during walking in people with multiple sclerosis

BACKGROUND

Balance and mobility impairment are two of the most common and debilitating symptoms among people with multiple sclerosis (MS). Somatosensory symptoms, including reduced plantar cutaneous sensation, have been identified in this cohort. Given the importance of the somatosensory system in gait, it is likely that impaired plantar sensation may play a role in the walking adaptations commonly observed in people with MS, including decreased stride length and increased stride width and dual support time, often described as a cautious gait strategy. Understanding the contributions of plantar sensation to these alterations may provide targets for interventions that seek to improve sensory feedback and normalize gait patterns. This cross-sectional study determined whether individuals with MS who demonstrate reduced sensitivity of the plantar surfaces also demonstrate altered plantar pressure distributions during walking compared to a control cohort.

METHODS

Twenty individuals with MS and twenty age- and sex-matched control participants walked barefoot at preferred and three matched speeds. Participants walked across a walkway with an embedded pressure plate used to quantify pressures within ten plantar zones. In addition, vibration perception thresholds were assessed at four sites on the plantar surface.

RESULTS

Individuals with MS demonstrated increased peak total plantar pressures compared to control participants, that increased with walking speed. For the MS group, plantar pressures were higher on the less sensitive foot, although pressures on both feet exceeded those of the control cohort. Positive correlations between vibration perception threshold and peak total pressure were evident, although generally stronger in the MS cohort.

CONCLUSION

A relationship between plantar vibration sensitivity and pressure could indicate that individuals with MS seek to increase plantar sensory feedback during walking. However, because proprioception may also be impaired, increased plantar pressure could result from inaccurate foot placement. Interventions targeting improved somatosensation may have the potential to normalize gait patterns and should be investigated.

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.

Does plantar skin abrasion affect cutaneous mechanosensation?

In humans, plantar cutaneous mechanoreceptors provide critical input signals for postural control during walking and running. Because these receptors are located within the dermis, the mechanical properties of the overlying epidermis likely affect the transmission of external stimuli. Epidermal layers are highly adaptable and can form hard and thick protective calluses, but their effects on plantar sensitivity are currently disputed. Some research has shown no effect of epidermal properties on sensitivity to vibrations, whereas other research suggests that vibration and touch sensitivity diminishes with a thicker and harder epidermis. To address this conflict, we conducted an intervention study where 26 participants underwent a callus abrasion while an age-matched control group (n = 16) received no treatment. Skin hardness and thickness as well as vibration perception thresholds and touch sensitivity thresholds were collected before and after the intervention. The Callus abrasion significantly decreased skin properties. The intervention group exhibited no change in vibration sensitivity but had significantly better touch sensitivity. We argue that touch sensitivity was impeded by calluses because hard skin disperses the monofilament's standardized pressure used to stimulate the mechanoreceptors over a larger area, decreasing indentation depth and therefore stimulus intensity. However, vibration sensitivity was unaffected because the vibrating probe was adjusted to reach specific indentation depths, and thus stimulus intensity was not affected by skin properties. Since objects underfoot necessarily indent plantar skin during weight-bearing, calluses should not affect mechanosensation during standing, walking, or running.

The effects of foot orthoses and sensory facilitation on lower limb electromyography: A scoping review

Foot orthoses (FO) are used as a treatment for biomechanical abnormalities, overuse injuries, and neuropathologies, but study of their mechanism remains inconclusive. The neuromotor paradigm has proposed that FOs may manipulate sensory input from foot sole skin to reduce muscle activity for movement optimization. This review argues that a FO likely alters the incoming mechanical stimuli transmitted via cutaneous mechanoreceptors and nociceptors as the foot sole interfaces with the surface of the orthotic. Thus, all FOs with or without intentional sensory facilitation, likely changes sensory information from foot sole cutaneous afferents. Additionally, in light of understanding and applying knowledge pertaining to the cutaneous reflex loop circuitry, FO's increasing sensory input to the motorneuron pool can change EMG to either reflex sign (increase or decrease). The purpose of this scoping review was to synthesize FO and sensory augmentation literature and summarize how FO designs can capitalize on foot sole skin to modulate lower limb electromyography (EMG). Six database searches resulted in 30 FO studies and 22 sensory studies that included EMG as an outcome measure. Results revealed task and phase specific responses with some consistencies in EMG outcomes between testing modalities, however many inconsistencies remain. Electrical stimulation reflex research provides support for a likely sensory-to-motor factor contributing to muscle activity modulation when wearing FOs. The discussion divides trends in FO treatment modalities by desired increase or decrease in each compartment musculature. The results of this review provides a benchmark for future academics and clinicians to advance literature in support of a revised neuromotor paradigm while highlighting the importance of foot sole skin in FO design.

Effect of vibrotactile stimulation of the hallux nail on segmental coordination: A secondary analysis using uncontrolled manifold analysis

Controlling center of mass (CoM) movement in the mediolateral direction is imperative for stable walking. During walking, CoM movement is adjusted by the coordination of each body segment, which can be evaluated using uncontrolled manifold (UCM) analysis. UCM analysis evaluates segmental coordination by analyzing variablity in motor movement among the different segments of the body. The vibrotactile stimulation of the hallux nail can augment the sensory information of the plantar surface for necessary motor control. This study aims to investigate the effect of the vibrotactile stimulation of the hallux nail on segmental coordination to control CoM movement in the mediolateral direction during walking. Thirteen healthy men participated in the study. A vibrator was attached to each hallux nail, and pressure sensors were placed under the hallux balls. When the hallux ball was in contact with the floor, vibration stimulation was applied. A three-dimensional motion analysis system was used to measure the segment angles during walking, and UCM analysis was used to evaluate kinematic synergy for controlling CoM movement in the mediolateral direction. Subsequently, segment angles were used as an elemental variable. The synergy index and bad variability as motor noise were negatively related to the status without the stimulation. Vibrotactile stimulation in young people was more effective for people with large motor noise and a small synergy index during the single-stance phase. Thus, kinematic synergy can be immediately changed by sensory input using vibrotactile stimulation of the hallux nail, although applying vibration stimulation should be considered in advance.

A comparison of the efficacy of textured insoles on balance performance in older people with versus without plantar callosities

BACKGROUND

Textured insoles have been suggested to enhance foot sensation, which contributes to controlling upright balance. However, the interaction between plantar callosity and the textured surface has not been studied.

RESEARCH QUESTION

Firstly, to compare the efficacy of textured insoles on balance performance and foot position sense between two groups of older people: one group had plantar callosity, and the other did not. Secondly, to investigate the efficacy of textured insoles within each study group.

METHODS

Thirty older people with a history of falls (15 with plantar callosity and 15 without callosity) participated in this study. All participants underwent assessments of postural sway on a force plate, joint position sensation of the ankle with a slope box, and mobility using the "Timed Up and Go" test under three insole surface conditions: 1) smooth (control), 2) placebo and 3) textured surface. Two-way analyses of variance were used to compare the outcomes of the two groups and three conditions.

RESULTS

Older people with plantar callosity had worse ankle joint position sense and slower antero-posterior and mediolateral postural sway velocity than their peers who did not have plantar callosity. The textured insoles improved ankle joint position sense and mobility regardless of callus status in the plantar surface of older peoples' feet. The insole-callosity interaction was not significant for any study outcome.

SIGNIFICANCE

Textured insoles could be beneficial to older people with and without callosity as they have shown immediate improvements in ankle joint position sense and mobility.

Cutaneous Sensitivity Across Regions of the Foot Sole and Dorsum are Influenced by Foot Posture

Understanding the processing of tactile information is crucial for the development of biofeedback interventions that target cutaneous mechanoreceptors. Mechanics of the skin have been shown to influence cutaneous tactile sensitivity. It has been established that foot skin mechanics are altered due to foot posture, but whether these changes affect cutaneous sensitivity are unknown. The purpose of this study was to investigate the potential effect of posture-mediated skin deformation about the ankle joint on perceptual measures of foot skin sensitivity. Participants (N = 20) underwent perceptual skin sensitivity testing on either the foot sole (N = 10) or dorsum (N = 10) with the foot positioned in maximal dorsiflexion/toe extension, maximal plantarflexion/toe flexion, and a neutral foot posture. Perceptual tests included touch sensitivity, stretch sensitivity, and spatial acuity. Regional differences in touch sensitivity were found across the foot sole (p < 0.001) and dorsum (p < 0.001). Touch sensitivity also significantly increased in postures where the skin was compressed (p = 0.001). Regional differences in spatial acuity were found on the foot sole (p = 0.002) but not dorsum (p = 0.666). Spatial acuity was not significantly altered by posture across the foot sole and dorsum, other than an increase in sensitivity at the medial arch in the dorsiflexion posture (p = 0.006). Posture*site interactions were found for stretch sensitivity on the foot sole and dorsum in both the transverse and longitudinal directions (p < 0.005). Stretch sensitivity increased in postures where the skin was pre-stretched on both the foot sole and dorsum. Changes in sensitivity across locations and postures were believed to occur due to concurrent changes in skin mechanics, such as skin hardness and thickness, which follows our previous findings. Future cutaneous biofeedback interventions should be applied with an awareness of these changes in skin sensitivity, to maximize their effectiveness for foot sole and dorsum input.

Applying Supra- or Sub-Threshold Plantar Vibrations Increases the Toe Clearance While Stepping over an Obstacle

This study aimed to investigate the effect of plantar vibrations on obstacle negotiation. Nineteen healthy young adults were randomly instructed to step over an obstacle without, with sub-, or with supra-threshold vibration via three vibrotactile tactors. The spatial-temporal gait parameters, the lower extremity joint angles, the foot integrated pressure, and the foot integrated area were recorded. Results indicated that sub-threshold and supra-threshold vibration increased the toe clearance of both leading leg and trailing legs. Additionally, the vibrations also increased the foot integrate pressure and the hip angels during toe clearance on both sides. These findings were devoted to the further understanding of the processes underlying motor control when plantar sensation was manipulated. These observations could further be used for developing a rehabilitation protocol for patients who suffered the loss or deterioration of the somatosensory system.

Plantar sensation, plantar pressure, and postural stability alterations and effects of visual status in older adults

PURPOSE

Ageing leads to plantar sensation and pressure alterations and poor postural control. The aim of this study was to compare the plantar sensation and static plantar pressure distribution between young and older adults. A secondary aim was to investigate the effect of ageing and visual status on postural stability.

MATERIALS AND METHODS

Forty older subjects and 43 young adult individuals participated in the study. Plantar light touch sensation was evaluated using Semmes-Weinstein monofilaments. Static plantar pressure and postural stability were assessed with the WinTrack^® Pedobarography device.

RESULTS

Plantar sensation thresholds of the older individuals were higher compared to the young in all plantar regions (p < 0.001). The plantar contact area was greater in older individuals (p < 0.001). Maximum plantar pressure of midfoot was higher and maximum plantar pressure of the rearfoot and whole foot was less in older individuals during quiet stance (p < 0.05). The main effects of group and visual condition were significant for mean latero-lateral and antero-posterior sway speed with large effect sizes (p < 0.05).

CONCLUSIONS

The sensation of all plantar regions reduced, the rearfoot plantar pressure decreased, and the midfoot plantar pressure increased in older individuals compared to young. Postural stability was reduced in the older individuals, and their postural control was more affected by the eliminated visual information compared to the young. Increased plantar contact area and midfoot plantar pressure may be related to decreased MLA height in older individuals. Older individuals may need visual information more to maintain postural control because of reduced plantar sensation.

Application of Real-Time Visual Feedback System in Balance Training of the Center of Pressure with Smart Wearable Devices

Balance control with an upright posture is affected by many factors. This study was undertaken to investigate the effects of real-time visual feedback training, provided by smart wearable devices for COP changes for healthy females, on static stance. Thirty healthy female college students were randomly divided into three groups (visual feedback balance training group, non-visual feedback balance training group, and control group). Enhanced visual feedback on the screen appeared in different directions, in the form of fluctuations; the visual feedback balance training group received real-time visual feedback from the Podoon APP for training, while the non-visual feedback balance training group only performed an open-eye balance, without receiving real-time visual feedback. The control group did not do any balance training. The balance training lasted 4 weeks, three times a week for 30 min each time with 1-2 day intervals. After four weeks of balance training, the results showed that the stability of human posture control improved for the one leg static stance for the visual feedback balance training group with smart wearable devices. The parameters of COP max displacement, COP velocity, COP radius, and COP area in the visual feedback balance training group were significantly decreased in the one leg stance (p < 0.05). The results showed that the COP real-time visual feedback training provided by smart wearable devices can better reduce postural sway and improve body balance ability than general training, when standing quietly.

Tegotae-Based Control Produces Adaptive Inter- and Intra-limb Coordination in Bipedal Walking

Despite the appealing concept of central pattern generator (CPG)-based control for bipedal walking robots, there is currently no systematic methodology for designing a CPG-based controller. To remedy this oversight, we attempted to apply the Tegotae approach, a Japanese concept describing how well a perceived reaction, i.e., sensory information, matches an expectation, i.e., an intended motor command, in designing localised controllers in the CPG-based bipedal walking model. To this end, we developed a Tegotae function that quantifies the Tegotae concept. This function allowed incorporating decentralised controllers into the proposed bipedal walking model systematically. We designed a two-dimensional bipedal walking model using Tegotae functions and subsequently implemented it in simulations to validate the proposed design scheme. We found that our model can walk on both flat and uneven terrains and confirmed that the application of the Tegotae functions in all joint controllers results in excellent adaptability to environmental changes.

An investigation of the effect of the lower extremity sensation on gait in children with cerebral palsy

BACKGROUND

Sensory disorders frequently accompany the motor disorders in children with cerebral palsy (CP).

RESEARCH QUESTION

Do children with CP have sensory disturbances in their lower extremities? If there are sensory impairments, do these impairments affect gait?

METHODS

In total, 45 children (18 females, 27 males) in an age range between 5 and 18 years were included in the study: 15 typically developing children, 15 unilaterally affected children with cerebral palsy, and 15 bilaterally affected children with cerebral palsy. They could walk independently at the levels of I or II according to the gross motor function classification. After the demographic data of the children were recorded, their tactile sense, vibration sense, two-point discrimination, and proprioception were evaluated, and the Edinburgh Visual Gait Score (EVGS) was used for gait assessment.

RESULTS

Failures were discovered in lower extremity tactile (p = 0.001), two-point discrimination (p = 0.001), and proprioceptive senses of the children with CP (p = 0.001), and the loss of tactile sense was found to be related to gait disorders (p = 0.02, r = 0.41).

SIGNIFICANCE

There were deficiencies in the lower extremity senses, and deficiencies in the tactile sense negatively affected gait. Performing sensory assessments, which are considered to be fundamental for gait training in the rehabilitation of children with CP, and providing support for the lacking parameters in the intervention programs may create positive effects on gait.

Postural performance and plantar cutaneous vibration perception in patients with idiopathic normal pressure hydrocephalus

Objective

To investigate whether impaired plantar cutaneous vibration perception contributes to postural disturbance in idiopathic normal pressure hydrocephalus (iNPH).

Methods

Three different groups were tested: iNPH-patients (iNPH), iNPH-patients after surgical shunt therapy (iNPH shunt), and healthy subjects (HS). Postural performance was quantified during quiescent stance on a pressure distribution platform. Vibration perception threshold (VPT) was measured using a modified vibration exciter to apply stimuli to the plantar foot.

Results

Regarding postural performance, iNPH showed significantly higher values for all investigated center of pressure (COP)-parameters compared to HS, which suggests impaired postural control. Shunted patients presented a tendency towards better postural control in contrast to non-shunted patients. VPTs did not differ significantly between all investigated groups, which suggests comparable plantar cutaneous vibration perception.

Conclusion

Patients with iNPH suffer from poor postural stability, whereas shunting tends to affect postural performance positively. Plantar cutaneous vibration perception seems to be comparable between all investigated study groups. Consequently, postural disturbance in iNPH cannot clearly be ascribed to defective plantar cutaneous input.

Sensory-to-Motor Overflow: Cooling Foot Soles Impedes Squat Jump Performance

Evidence from recent studies on animals and humans suggest that neural overflow from the primary sensory cortex (S1) to the primary motor cortex (M1) may play a critical role in motor control. However, it is unclear if whole-body maximal motor tasks are also governed by this mechanism. Maximum vertical squat jumps were performed by 15 young adults before cooling, then immediately following a 15-min cooling period using an ice-water bath for the foot soles, and finally immediately following a 15-min period of natural recovery from cooling. Jump heights were, on average, 3.1 cm lower immediately following cooling compared to before cooling (p = 3.39 × 10⁻⁸) and 1.9 cm lower following natural recovery from cooling (p = 0.00124). The average vertical ground reaction force (vGRF) was also lower by 78.2 N in the condition immediately following cooling compared to before cooling (p = 8.1 × 10⁻⁵) and 56.7N lower following natural recovery from cooling (p = 0.0043). The current study supports the S1-to-M1 overflow mechanism in a whole-body dynamic jump.

Vibrotactile Stimulation of Nail of Hallux during Walking: Effect on Center-of-Mass Movement in Healthy Young Adults

Previous studies have reported that vibrotactile stimulation of the nail of the hallux decreases the variability of the center-of-mass (CoM) movement in the lateral direction in subjects performing unsteady walking on the spot. This study investigated the effect of vibrotactile stimulation of the nail of the hallux on the CoM movement during walking. Healthy young males were asked to walk with and without stimulation, and their CoM was measured. The intrasubject mean and coefficient of variation (CV) of their walking speed, stance time, and CoM movement were evaluated. The differences between the variables with and without stimulation were determined, and the baseline-dependent effects of the stimulation on these variables were analyzed. It was observed that stimulation had a negative baseline-dependent effect on the CVs of the walking speed, stance time, and the CoM movement in the lateral direction. In particular, stimulation decreased the CV of the CoM movement in the lateral direction for subjects with a greater variability. Vibrotactile stimulation of the nail of the hallux can reduce the variability of the lateral displacement of the CoM movement in healthy young subjects who otherwise show a large variability of the CoM movement during walking without stimulation.

Ambulatory searching task reveals importance of somatosensation for lower-limb amputees

The contribution of somatosensation to locomotor deficits in below-knee amputees (BKAs) has not been fully explored. Unilateral disruption of plantar sensation causes able-bodied individuals to adopt locomotor characteristics that resemble those of unilateral BKAs, suggesting that restoring somatosensation may improve locomotion for amputees. In prior studies, we demonstrated that electrically stimulating the residual nerves of amputees elicited somatosensory percepts that were felt as occurring in the missing foot. Subsequently, we developed a sensory neuroprosthesis that modulated stimulation-evoked sensation in response to interactions between the prosthesis and the environment. To characterize the impact of the sensory neuroprosthesis on locomotion, we created a novel ambulatory searching task. The task involved walking on a horizontal ladder while blindfolded, which engaged plantar sensation while minimizing visual compensation. We first compared the performance of six BKAs to 14 able-bodied controls. Able-bodied individuals demonstrated higher foot placement accuracy than BKAs, indicating that the ladder test was sensitive enough to detect locomotor deficits. When three of the original six BKAs used the sensory neuroprosthesis, the tradeoff between speed and accuracy significantly improved for two of them. This study advanced our understanding of how cutaneous plantar sensation can be used to acquire action-related information during challenging locomotor tasks.

Laterality of toe grip strength in Kendo players

[Purpose] The purpose of this study was to determine whether unilateral dominance exists in toe grip strength in Kendo players using a toe grip dynamometer. [Participants and Methods] In total, 15 male college Kendo players, who had no disability or pain in their feet, were included in the study. The participants completed a questionnaire to determine which foot the participants used as their front and rear foot while standing in Kendo. We measured toe grip strength three times on each side. We then extracted the maximum value of toe grip strength from the three measurements on each side and calculated the ratio of toe grip strength to body weight (%). [Results] All players used their right foot as the front foot. We found that the front foot toe grip strength was significantly stronger than the rear foot toe grip strength. [Conclusion] Our results suggest laterality of toe grip strength and the front foot toe grip strength is stronger than the rear foot toe grip strength in Kendo players.

The contribution of small and large sensory afferents to postural control in patients with peripheral neuropathy

Peripheral neuropathy (PN) is a multifarious disorder that is caused by damage to the peripheral nerves. Although the symptoms of PN vary with the etiology, most cases are characterized by impaired tactile and proprioceptive sensation that progresses in a distal to proximal manner. Balance also tends to deteriorate as the disorder becomes more severe, and those afflicted are substantially more likely to fall while walking compared with those who are healthy. Most patients with PN walk more cautiously and with greater stride variability than age-matched controls, but the majority of their falls occur when they must react to a perturbation such as a slippery or uneven surface. The purpose of this study was to first describe the role of somatosensory feedback in the control of posture and then discuss how that relationship is typically affected by the most common types of PN. A comprehensive review of the scientific literature was conducted using MEDLINE, and the relevant information was synthesized. The evidence indicates that the proprioceptive feedback that is conveyed primarily through larger type I afferents is important for postural control. However, the evidence indicates that the tactile feedback communicated through smaller type II afferents is particularly critical to the maintenance of balance. Many forms of PN often lead to chronic tactile desensitization in the soles of the feet and, although the central nervous system seems to adapt to this smaller type II afferent dysfunction by relying on more larger type I afferent reflex loops, the result is still decreased stability. We propose a model that is intended both to help explain the relationship between stability and the smaller type II afferent and the larger type I afferent feedback that may be impaired by PN and to assist in the development of pertinent rehabilitative interventions.

Effects of foot position on skin structural deformation

As the largest and most superficial organ, the skin is well positioned for receiving sensory information from the environment. It is conceivable that changes in posture could result in deformations of the skin and subsequent changes in skin material properties. Specifically, the ankle and metatarsophalangeal joints have the capability to undergo large postural alterations with the potential to induce large structural deformations in the skin of the foot. The purpose of this study was to determine the extent to which alterations in foot posture may influence measures of foot sole and dorsum skin stretch, hardness, and thickness in vivo. Ten young and healthy individuals were tested while three static foot postures (plantar flexion, neutral and dorsiflexion) were maintained passively. Skin stretch deformation was quantified across each posture using an 11 × 4 point matrix of 3D kinematic markers affixed to the skin of the foot sole and dorsum. Skin hardness was assessed across each posture at specific locations of the foot sole (1st metatarsal, 5th metatarsal, medial arch, lateral arch and heel) and foot dorsum (proximal, middle and distal) using a handheld Shore durometer. Skin (epidermal + dermal) thickness was measured in each posture from the same test locations using ultrasound images obtained for the foot sole and dorsum. In the plantar flexion ankle posture, the foot sole skin was observed to relax/retract on average (± standard errorr of the mean (SEM) by 9 ± 2% to become both 20 ± 6% softer and 10 ± 6% thicker. In this posture, the foot dorsum skin stretched on average by 7 ± 2% resulting in 84 ± 8% harder and 5 ± 4% thinner skin. In the dorsiflexion ankle posture, the skin of the foot sole was observed to stretch on average by 5 ± 1% to become both 20 ± 8% harder and 4 ± 7% thinner. In this posture, the skin of the foot dorsum relaxed/retracted on average by 9 ± 1% resulting in the skin becoming 27 ± 12% softer and 7 ± 5% thicker. Notably, all of the sites responded with movement in a similar direction, but each site responded to a variable extent. Importantly, it was clear that the majority of skin structural deformation of the foot sole occurred within the 1st metatarsal, 5th metatarsal, and medial arch regions, while deformation was more evenly distributed across regions of the foot dorsum. The results suggest there is location specificity in the retraction and stretch characteristics of the foot skin. While not tested directly, this may suggest that local stretch distributions could be in part due to the underlying dermal and hypodermal structures in these foot regions. With these observed changes in the mechanical structure of the foot sole and dorsum skin tissue matrix, it is possible that corresponding posture-dependent changes in cutaneous mechanoreceptor activation may be present.

Effects of toe spreader on plantar pressure and gait in chronic stroke patients

BACKGROUND

The feet make the initial contact with the ground when walking and critically control both posture and gait. Claw toe, a structural change in the foot that may develop after stroke, triggers functional changes affecting both the lower limbs and balance.

OBJECTIVE

We analyzed the effects of a toe spreader on foot pressure and gait in chronic stroke patients.

METHODS

We enrolled 25 stroke patients. We used Gaitview AFA-50 and GAITRite instruments to measure plantar pressure distribution and gait with and without a toe spreader.

RESULTS

The average and rear foot pressures increased somewhat when a toe spreader was used. However, the differences were not significant in post hoc tests. In terms of gait, all variables significantly improved when the toe spreader was used.

CONCLUSIONS

A toe spreader may improve overall gait and spatiotemporal gait parameters in chronic stroke patients.

Transcranial direct current stimulation modulates the brain's response to foot stimuli under dual-task condition: A fMRI study in elderly adults

Previous behavioral studies have shown that high-intensity cognitive tasks weaken balance control in elder adults. Moreover, age-related loss of plantar sensation is considered to be an important contributing factor to the occurrence of falls. Recently, we have realized that transcranial direct current stimulation (tDCS) can effectively improve the balance of the elderly under the dual-task, but its underlying regulatory mechanism is not clear. In this study, task functional Magnetic Resonance Imaging (fMRI) was used to study the brain's response to foot stimuli under foot stimuli or dual-task (foot stimuli and cognitive task) conditions to explain the effect of the addition of cognitive tasks during balance in 16 healthy elderly adults. To study whether tDCS would counteract the effect of the added cognitive task, we further compared the differences in activity of the cerebral cortices of dual-task and tDCS-dual-task conditions. The results suggested added cognitive tasks significantly attenuated the response of the brain to foot stimuli in elderly adults. Moreover, the cortex excitability weakened by cognitive tasks was significantly promoted after 20 min of tDCS. In conclusion, a portion of the resources originally used for plantar sensory processing may be assigned to the processing of the cognitive task when the cognitive tasks are added, which results in insufficient resources for plantar sensory processing. tDCS improves the ability of the brain to respond to foot stimuli by modulating the excitability of the cognitive cortex and reverses the effects of cognitive tasks.

Cutaneous afferent innervation of the human foot sole: what can we learn from single-unit recordings?

Cutaneous afferents convey exteroceptive information about the interaction of the body with the environment and proprioceptive information about body position and orientation. Four classes of low-threshold mechanoreceptor afferents innervate the foot sole and transmit feedback that facilitates the conscious and reflexive control of standing balance. Experimental manipulation of cutaneous feedback has been shown to alter the control of gait and standing balance. This has led to a growing interest in the design of intervention strategies that enhance cutaneous feedback and improve postural control. The advent of single-unit microneurography has allowed the firing and receptive field characteristics of foot sole cutaneous afferents to be investigated. In this review, we consolidate the available cutaneous afferent microneurographic recordings from the foot sole and provide an analysis of the firing threshold, and receptive field distribution and density of these cutaneous afferents. This work enhances the understanding of the foot sole as a sensory structure and provides a foundation for the continued development of sensory augmentation insoles and other tactile enhancement interventions.

Adding body load modifies the vibratory sensation of the foot sole and affects the postural control

BACKGROUND

Heavy backpacks are often used by soldiers and firefighters. Weight carrying could reduce the speed and efficiency in task completion by altering the foot sole sensitivity and postural control.

METHODS

In fifteen healthy subjects, we measured the changes in sensitivity to vibrations applied to the foot sole when standing upright or walking after load carrying (30% body weight). The participants were asked to judge different vibration amplitudes applied on the 2nd or 5th metatarsal head and the heel at two frequencies (25 and 150 Hz) to determine the vibration threshold and the global perceptual representation (Ѱ)of the vibration amplitude (Ф) given by the Stevens power function (Ѱ = k × Фn). Any increase in negative k value indicated a reduction in sensitivity to the lowest loads. Pedobarographic measurements, with computation of the center of pressure (COP) and its deviations, were performed during weight carrying.

RESULTS

The 25-Hz vibration threshold significantly increased after weight carrying when standing upright or walking. After standing with the added loads, the absolute negative k value increased for the 25 Hz frequency. After walking with the added loads, the k coefficient increased for the two vibration frequencies. Weight carrying significantly increased both the CoP surface and CoP lateral deviation.

CONCLUSIONS

Our data show that weight carrying reduces the sensory pathways from the foot sole and accentuates the center of pressure deviations.

Effect of insoles with arch support on gait pattern in patients with multiple sclerosis

Objectives

This study aims to determine the effect of insoles with arch support on gait patterns in patients with multiple sclerosis (MS) and somatosensory impairment.

Patients and methods

Ten patients (7 females, 3 males; mean age 34.9±6.8 years; range, 48 to 35 years) with clinically definite relapsing remitting MS and age- and sex-matched 10 healthy volunteers (7 females, 3 males; mean age 33.8±3.2; range, 40 to 31 years) were included in the study between January 2011 and January 2012. A medial longitudinal arch and transverse arch supporting polyurethane insole covered with foam shaped using plantar sensory feedback was used. Three-dimensional gait analysis was performed via a Vicon 612 system with six cameras. The participants initially walked barefoot and, then, wore the insoles in their short slipper socks.

Results

All participants were evaluated in terms of kinetics, kinematics, and temporospatial parameters with a gait analysis system. The patients with MS showed improvements in cadence and walking speed when using the insoles. Sagittal plane angles of the hip and knee were increased while using insoles (p<0.05) and ankle plantar flexion was found to be decreased, compared to barefoot walking (p<0.05).

Conclusion

Our study results suggest that insole with arch support affects gait cycle, but does not improve gait impairments in patients with MS. Insoles may ensure plantar sensory feedback in feet during walking, which increases pressure in the mid-forefoot area.

Transcranial direct current stimulation enhances foot sole somatosensation when standing in older adults

Foot-sole somatosensation is critical for safe mobility in older adults. Somatosensation arises when afferent input activates a neural network that includes the primary somatosensory cortex. Transcranial direct current stimulation (tDCS), as a strategy to increase somatosensory cortical excitability, may, therefore, enhance foot-sole somatosensation. We hypothesized that a single session of tDCS would improve foot-sole somatosensation, and thus mobility, in older adults. Twenty healthy older adults completed this randomized, double-blinded, cross-over study consisting of two visits separated by one week. On each visit, standing vibratory threshold (SVT) of each foot and the timed-up-and-go test (TUG) of mobility were assessed immediately before and after a 20-min session of tDCS (2.0 mA) or sham stimulation with the anode placed over C3 (according to the 10/20 EEG placement system) and the cathode over the contralateral supraorbital margin. tDCS condition order was randomized. SVT was measured with a shoe insole system. This system automatically ramped up, or down, the amplitude of applied vibrations and the participant stated when they could or could no longer feel the vibration, such that lower SVT reflected better somatosensation. The SVTs of both foot soles were lower following tDCS as compared to sham and both pre-test conditions [F_(1,76) > 3.4, p < 0.03]. A trend towards better TUG performance following tDCS was also observed [F_(1,76) = 2.4, p = 0.07]. Greater improvement in SVT (averaged across feet) moderately correlated with greater improvement in TUG performance (r = 0.48, p = 0.03). These results suggest that tDCS may enhance lower-extremity somatosensory function, and potentially mobility, in healthy older adults.

The Variation of Plantar Temperature and Plantar Pressure during Shod Running with Socks or not

Foot temperature can be affected by friction and contact pressure, in this study, we explored the specific changes of foot temperature under different friction conditions, running with socks versus no socks. The relationship between vertical loading force and foot temperature will also be investigated at the same time. Ten male recreational runners wore the same shoes and socks and were tested running 8km/h on a treadmill. The plantar temperature during running was recorded every 3 minutes for a total of 45 minutes. Post-run temperature change was recorded every 3 minutes for 12 minutes. The plantar pressure was recorded before running and at the first 15 minutes during running. The subjects with socks and no socks were tested on separate occasions. There were no significant differences found between the socks and no socks conditions. However, central metatarsal head, lateral metatarsal head, medial rearfoot and lateral rearfoot regions exist differences were reflected at the first 6minutes-12minutes of running. The foot temperature became more stable after 15minutes of running. Also, plantar pressure increased significantly in the hallux, other toes, first metatarsal head and central metatarsal regions. It also could conclude that lower initial temperature had a greater increase trend during the running start stage. When the ankle in plantarflexion stage, toe and forefoot regions showed a higher rise in temperature and also presented higher plantar pressure correspondingly.

A wearable vibrotactile biofeedback system improves balance control of healthy young adults following perturbations from quiet stance

Maintaining postural equilibrium requires fast reactions and constant adjustments of the center of mass (CoM) position to prevent falls, especially when there is a sudden perturbation of the support surface. During this study, a newly developed wearable feedback system provided immediate vibrotactile clues to users based on plantar force measurement, in an attempt to reduce reaction time and CoM displacement in response to a perturbation of the floor. Ten healthy young adults participated in this study. They stood on a support surface, which suddenly moved in one of four horizontal directions (forward, backward, left and right), with the biofeedback system turned on or off. The testing sequence of the four perturbation directions and the two system conditions (turned on or off) was randomized. The resulting reaction time and CoM displacement were analysed. Results showed that the vibrotactile feedback system significantly improved balance control during translational perturbations. The positive results of this preliminary study highlight the potential of a plantar force measurement based biofeedback system in improving balance under perturbations of the support surface. Future system optimizations could facilitate its application in fall prevention in real life conditions, such as standing in buses or trains that suddenly decelerate or accelerate.

Influence of functional task-oriented mental practice on the gait of transtibial amputees: a randomized, clinical trial

Background

Mental practice (MP) through motor imagery is a cognitive training strategy used to improve locomotor skills during rehabilitation programs. Recent works have used MP tasks to investigate the neurophysiology of human gait; however, its effect on functional performance has not been evaluated. In the present study, the influence of gait-oriented MP tasks on the rehabilitation process of gait in transtibial amputees was investigated by assessing the vertical (V), anterior-posterior (AP), and medio-lateral (ML) ground reaction forces (GRFs) and the time duration of the support phase of the prosthetic limb.

Methods

Unilateral transtibial amputees, who were capable of performing motor imagination tasks (MIQ-RS score ≥4), were randomly divided into two groups: Group A (n = 10), who performed functional gait-oriented MP combined with gait training, and Group B (n = 5), who performed non-motor task MP. The MP intervention was performed in the first-person perspective for 40 min, 3 times/week, for 4 weeks. The GRF outcome measures were recorded by a force platform to evaluate gait performance during 4 distinct stages: at baseline (BL), 1 month before the MP session; Pre-MP, 1–3 days before the MP session; Post-MP, 1–3 days after the MP session; and follow-up (FU), 1 month after MP session. The gait variables were compared inter- and intra-group by applying the Mann-Whitney and Friedman tests (alpha = 0.05).

Results

All volunteers exhibited a homogenous gait pattern prior to MP intervention, with no gait improvement during the BL and Pre-MP stages. Only Group A showed significant improvements in gait performance after the intervention, with enhanced impact absorption, as indicated by decreased first V and AP peaks; propulsion capacity, indicated by increasing second V and AP peaks; and balance control of the prosthetic limb, indicated by decreasing ML peaks and increasing duration of support. This gait pattern persisted until the FU stage.

Conclusions

MP combined with gait training allowed transtibial amputees to reestablish independent locomotion. Since the effects of MP were preserved after 1 month, the improvement is considered related to the specificity of the MP tasks. Therefore, MP may improve the clinical aspect of gait rehabilitation when included in a training program.

Effect of floating toes on knee and trunk acceleration during walking: a preliminary study

[Purpose] This study investigated the effect of floating toes on knee and trunk acceleration during walking in experimental setting. [Subjects and Methods] Twelve healthy volunteers walked barefoot at a preferred speed along a linear pathway under 2 conditions: normal gait (control) condition and floating toes (FT) condition. In the latter, weight bearing by the toes was avoided using kinesiology tape applied along the toe extensors. Accelerations of the knee (Kn) and lumbar spine (Lx) were assessed using triaxial accelerometers mounted on the right fibular head and the spinous process of L3. Acceleration vectors were oriented such that the anterior, right, and cranial deviations were positive along the anteroposterior, lateral, and vertical axes, respectively. The root mean squares (RMSs; anteroposterior, RMSap; lateral, RMSl; vertical, RMSv) were calculated, and the mean values of 3 trials in each condition were determined. Differences between the conditions were assessed using the Wilcoxon signed-rank test. [Results] LxRMSap and LxRMSv were larger in the FT condition than in the control condition. KnRMSv tended to be higher in the FT condition than in the control condition. [Conclusion] Floating toes increase acceleration and might create mechanical stress on the lower back and knee during walking.

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.

Short-Term Effect of Prosthesis Transforming Sensory Modalities on Walking in Stroke Patients with Hemiparesis

Sensory impairments caused by neurological or physical disorders hamper kinesthesia, making rehabilitation difficult. In order to overcome this problem, we proposed and developed a novel biofeedback prosthesis called Auditory Foot for transforming sensory modalities, in which the sensor prosthesis transforms plantar sensations to auditory feedback signals. This study investigated the short-term effect of the auditory feedback prosthesis on walking in stroke patients with hemiparesis. To evaluate the effect, we compared four conditions of auditory feedback from plantar sensors at the heel and fifth metatarsal. We found significant differences in the maximum hip extension angle and ankle plantar flexor moment on the affected side during the stance phase, between conditions with and without auditory feedback signals. These results indicate that our sensory prosthesis could enhance walking performance in stroke patients with hemiparesis, resulting in effective short-term rehabilitation.

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.

Effects of insoles contact on static balance

[Purpose] This study examined the effect of the degree of the contact area between the insoles and soles on static balance. [Subjects and Methods] Thirteen healthy male and female adults voluntarily participated. All of the subjects wore three different types of insoles (no orthotic insole, partial contact, full contact) in the present experiment. The subjects were instructed to place both feet parallel to each other and maintain static balance for 30 seconds. Center of pressure parameters (range, total distance, and mean velocity) were analyzed. [Results] The results show that the anteroposterior range and mediolateral (ML) total distance and velocity decreased when orthotic insoles with partial contact or full contact were used in comparison to when a flat insole (no orthotic insole) was used. Also, the ML range and total distance were lower with full contact than in the other two conditions. These results indicate that static balance improves as the degree of contact between the soles and insoles increases. [Conclusion] The results of this study suggests that using insoles with increased sole contact area would improve static balance ability.