Subsensory vibrations to the feet reduce gait variability in elderly fallers

Improving postural control by applying mechanical noise to ankle muscle tendons

The application of subthreshold mechanical vibrations with random frequencies (white mechanical noise) to ankle muscle tendons is known to increase muscle proprioceptive information and to improve the detection of ankle movements. The aim of the present study was to analyze the effect of this mechanical noise on postural control, its possible modulation according to the sensory strategies used for postural control, and the consequences of increasing postural difficulty. The upright stance of 20 healthy young participants tested with their eyes closed was analyzed during the application of four different levels of noise and compared to that in the absence of noise (control) in three conditions: static, static on foam, and dynamic (sinusoidal translation). The quiet standing condition was conducted with the eyes open and closed to determine the subjects' visual dependency to maintain postural stability. Postural performance was assessed using posturographic and motion analysis evaluations. The results in the static condition showed that the spectral power density of body sway significantly decreased with an optimal level of noise and that the higher the spectral power density without noise, the greater the noise effect, irrespective of visual dependency. Finally, noise application was ineffective in the foam and dynamic conditions. We conclude that the application of mechanical noise to ankle muscle tendons is a means to improve quiet standing only. These results suggest that mechanical noise stimulation may be more effective in more impaired populations.

Gait variability across the disability spectrum in people with multiple sclerosis

BACKGROUND

An alternative method suggested to assess changes in walking in people with multiple sclerosis (PwMS) is evaluating gait variability. This is a credible option since gait variability reflects to some degree the quality of gait control.

OBJECTIVE

Examine the impact of disability on gait variability in PwMS.

METHODS

In this cross-sectional study, the data pool was divided into seven levels of disability based on the Expanded Disability Status Scale (EDSS) score, ranging from 0 to 6.5. Gait variability was studied using an electronic mat.

RESULTS

The final analysis included 381 PwMS (249 women); mean age 44.0years. Non-significant differences were observed between the EDSS subgroups at the lower end of the spectrum (EDSS 0-3.5) in all gait variability parameters. In contrast, PwMS in the EDSS 5.0-5.5 group demonstrated a significant increase in variability of step length (~151%), single support (~93%) and step time (142%) compared with those who scored 0-3.5. Moreover, participants in the EDSS 5.0-5.5 group had elevated step length variability compared to the EDSS 4.0-4.5 group (9.3 (S.E.=2.2) vs. 5.5 (S.E.=0.4), P-value=0.005).

CONCLUSION

We encourage clinicians to follow-up on the gait variability score as it appears to reflect mobility deterioration in PwMS.

Stochastic Resonance Effects on Apnea, Bradycardia, and Oxygenation: A Randomized Controlled Trial

OBJECTIVE

To evaluate the effect of stochastic resonance (SR) stimulation on preterm infant oxygen desaturation, bradycardia, and apnea events. We hypothesized that SR stimulation will reduce these events.

METHODS

This was a randomized crossover study conducted from April 2012 to July 2014. Eligible preterm infants were not receiving ventilation support and had at least 1 clinically documented apnea, bradycardia, and/or oxygen desaturation event. The 3 outcome variables were as follows: oxygen desaturation, bradycardia, and apnea events. Infants received up to two 3- or 4-hour intervention periods of 30-minute alternating intervals of SR stimulation and no SR stimulation. The first intervention period was randomly assigned to begin with SR stimulation either on or off, whereas the next intervention period automatically began with the opposite on/off state. We compared the SR stimulation "on" periods with the SR stimulation "off" periods with each infant serving as his or her own control.

RESULTS

The sample consisted of 36 infants with a mean (±SD) gestational age of 30.5 ± 3 weeks and a birth weight of 1409 ± 450 g. SR stimulation decreased the number of apneic events by 50%. SR stimulation ameliorated every aspect of clinically significant oxygen desaturation events, with a 20% to 35% decrease in the number, duration, and intensity of oxygen desaturation events when SR stimulation was on. Also, SR stimulation produced a nearly 20% reduction in the intensity of bradycardia events.

CONCLUSIONS

SR stimulation may be a noninvasive and nonpharmacologic treatment option for apnea, oxygen desaturation, and some aspects of bradycardia in premature infants.

Sensory Enhancing Insoles Modify Gait during Inclined Treadmill Walking with Load

INTRODUCTION

Inclined walking while carrying a loaded backpack induces fatigue, which may destabilize gait and lead to injury. Stochastic resonance (SR) technology has been used to stabilize spatiotemporal gait characteristics of elderly individuals but has not been tested on healthy recreational athletes. Herein, we determined if sustained vigorous walking on an inclined surface while carrying a load destabilizes gait and if SR has a further effect.

METHODS

Participants were fitted with a backpack weighing 30% of their body weight and asked to walk at a constant self-selected pace while their feet were tracked using an optical motion capture system. Their shoes were fitted with SR insoles that were set at 90% of the participant's sensory threshold. The treadmill incline was increased every 5 min until volitional exhaustion after which the treadmill was returned to a level grade. SR stimulation was turned ON and OFF in a pairwise random fashion throughout the protocol. Spatiotemporal gait characteristics were calculated when SR was ON and OFF for the BASELINE period, the MAX perceived exertion period, and the POST period.

RESULTS

Vigorous activity increases variability in the rhythmic stepping (stride time and stride length) and balance control (double support time and stride width) mechanisms of gait. Overall, SR increased stride width variability by 9% before, during, and after a fatiguing exercise.

CONCLUSION

The increased stride time and stride length variability may compromise the stability of gait during and after vigorous walking. However, participants may compensate by increasing double support time and stride width variability to maintain their stability under these adverse conditions. Furthermore, applying SR resulted in an additional increase of stride width variability and may potentially improve balance before, during, and after adverse walking conditions.

Using low levels of stochastic vestibular stimulation to improve locomotor stability

Low levels of bipolar binaural white noise based imperceptible stochastic electrical stimulation to the vestibular system (stochastic vestibular stimulation, SVS) have been shown to improve stability during balance tasks in normal, healthy subjects by facilitating enhanced information transfer using stochastic resonance (SR) principles. We hypothesize that detection of time-critical sub-threshold sensory signals using low levels of bipolar binaural SVS based on SR principles will help improve stability of walking during support surface perturbations. In the current study 13 healthy subjects were exposed to short continuous support surface perturbations for 60 s while walking on a treadmill and simultaneously viewing perceptually matched linear optic flow. Low levels of bipolar binaural white noise based SVS were applied to the vestibular organs. Multiple trials of the treadmill locomotion test were performed with stimulation current levels varying in the range of 0–1500 μA, randomized across trials. The results show that subjects significantly improved their walking stability during support surface perturbations at stimulation levels with peak amplitude predominantly in the range of 100–500 μA consistent with the SR phenomenon. Additionally, objective perceptual motion thresholds were measured separately as estimates of internal noise while subjects sat on a chair with their eyes closed and received 1 Hz bipolar binaural sinusoidal electrical stimuli. The optimal improvement in walking stability was achieved on average with peak stimulation amplitudes of approximately 35% of perceptual motion threshold. This study shows the effectiveness of using low imperceptible levels of SVS to improve dynamic stability during walking on a laterally oscillating treadmill via the SR phenomenon.

Haptic wearables as sensory replacement, sensory augmentation and trainer - a review

Sensory impairments decrease quality of life and can slow or hinder rehabilitation. Small, computationally powerful electronics have enabled the recent development of wearable systems aimed to improve function for individuals with sensory impairments. The purpose of this review is to synthesize current haptic wearable research for clinical applications involving sensory impairments. We define haptic wearables as untethered, ungrounded body worn devices that interact with skin directly or through clothing and can be used in natural environments outside a laboratory. Results of this review are categorized by degree of sensory impairment. Total impairment, such as in an amputee, blind, or deaf individual, involves haptics acting as sensory replacement; partial impairment, as is common in rehabilitation, involves haptics as sensory augmentation; and no impairment involves haptics as trainer. This review found that wearable haptic devices improved function for a variety of clinical applications including: rehabilitation, prosthetics, vestibular loss, osteoarthritis, vision loss and hearing loss. Future haptic wearables development should focus on clinical needs, intuitive and multimodal haptic displays, low energy demands, and biomechanical compliance for long-term usage.

Thresholds of skin sensitivity are partially influenced by mechanical properties of the skin on the foot sole

Across the foot sole, there are vibration and monofilament sensory differences despite an alleged even distribution of cutaneous afferents. Mechanical property differences across foot sole sites have been proposed to account for these differences. Vibration (VPT; 3 Hz, 40 Hz, 250 Hz), and monofilament (MF) perception threshold measurements were compared with skin hardness, epidermal thickness, and stretch response across five foot sole locations in young healthy adults (n = 22). Perceptual thresholds were expected to correlate with all mechanical property measurements to help address sensitivity differences between sites. Following this hypothesis, the MedArch was consistently found to be the thinnest and softest site and demonstrated the greatest sensitivity. Conversely, the Heel was found to be the thickest and hardest site, and was relatively insensitive across perceptual tests. Site differences were not observed for epidermal stretch response measures. Despite an apparent trend of elevated sensory threshold at harder and thicker sites, significant correlations between sensitivity measures and skin mechanical properties were not observed. Skin hardness and epidermal thickness appeared to have a negligible influence on VPT and minor influence on MF within this young healthy population. When normalized (% greater or smaller than subject mean) to the subject mean for each variable, significant positive correlations were observed between MF and skin hardness (R² = 0.422, P < 0.0001) and epidermal thickness (R² = 0.433, P < 0.0001) providing evidence that skin mechanics can influence MF threshold. In young healthy adults, differences in sensitivity are present across the foot sole, but cannot solely be accounted for by differences in the mechanical properties of the skin.

Effects of aging and tactile stochastic resonance on postural performance and postural control in a sensory conflict task

Postural control in certain situations depends on functioning of tactile or proprioceptive receptors and their respective dynamic integration. Loss of sensory functioning can lead to increased risk of falls in challenging postural tasks, especially in older adults. Stochastic resonance, a concept describing better function of systems with addition of optimal levels of noise, has shown to be beneficial for balance performance in certain populations and simple postural tasks. In this study, we tested the effects of aging and a tactile stochastic resonance stimulus (TSRS) on balance of adults in a sensory conflict task. Nineteen older (71-84 years of age) and younger participants (22-29 years of age) stood on a force plate for repeated trials of 20 s duration, while foot sole stimulation was either turned on or off, and the visual surrounding was sway-referenced. Balance performance was evaluated by computing an Equilibrium Score (ES) and anterior-posterior sway path length (APPlength). For postural control evaluation, strategy scores and approximate entropy (ApEn) were computed. Repeated-measures ANOVA, Wilcoxon signed-rank tests, and Mann-Whitney U-tests were conducted for statistical analysis. Our results showed that balance performance differed between older and younger adults as indicated by ES (p = 0.01) and APPlength (0.01), and addition of vibration only improved performance in the older group significantly (p = 0.012). Strategy scores differed between both age groups, whereas vibration only affected the older group (p = 0.025). Our results indicate that aging affects specific postural outcomes and that TSRS is beneficial for older adults in a visual sensory conflict task, but more research is needed to investigate the effectiveness in individuals with more severe balance problems, for example, due to neuropathy.

Footwear interventions: a review of their sensorimotor and mechanical effects on balance performance and gait in older adults

Footwear interventions, including shoe insoles and foot orthoses, have the capacity to enhance balance control and gait in older people. This review assessed the evidence for the effect of footwear interventions on static and dynamic balance performance and gait in older populations and explored proposed theories for underlying sensorimotor and mechanical mechanisms. We searched the Medline, EMBASE, CINAHL (the Cumulative Index to Nursing and Allied Health Literature), and AMED databases and conducted hand searches. Of 115 relevant articles screened, 14 met the predefined inclusion criteria. Articles were grouped into one of three categories based on balance task (static balance performance during quiet standing, dynamic balance performance during walking, and dynamic balance performance during perturbed standing or functional tasks) and were scored for methodological quality using the Downs and Black Quality Index tool. Footwear interventions seem to alter underlying strategies controlling static and dynamic movement patterns through a combination of sensorimotor and mechanical mechanisms in older people, including those with chronic sensory and musculoskeletal conditions. Evidence shows a consistent trend toward footwear interventions markedly improving lateral stability measures, which are predictors of falls in the elderly. In-depth investigation of neurophysiologic responses to footwear interventions is necessary to help confirm any sensorimotor adaptations. The long-term effects of footwear interventions on balance, gait, and the prevention of falls in older people require further investigation.

Impacts of different types of insoles on postural stability in older adults

The objective of this study was to examine the effects of different types of insoles on postural stability in older adults. Four types of commercially available insoles were selected including the cupped insoles, textured insoles, rigid insoles, and soft insoles. The experiment included a static stance session and a walking session. In the static stance session, the participants stood upright on a force platform as still as possible, with feet together, arms by the side and looking straight ahead. The mean velocity of center-of-pressure time series obtained from the force platform was used to assess static postural stability. In the walking session, the participants walked on a treadmill at their self-selected comfortable speed for 4.5 min in each insole condition. Dynamic postural stability was assessed using the margin of stability. It was found that static postural stability was not affected by insoles, but cupped insoles improved dynamic postural stability, and rigid insole was associated with better dynamic postural stability compared to soft insoles. These findings can aid in better understanding the insole design features associated with improved postural stability in older adults.

Effect of remote sensory noise on hand function post stroke

Hand motor impairment persists after stroke. Sensory inputs may facilitate recovery of motor function. This pilot study tested the effectiveness of tactile sensory noise in improving hand motor function in chronic stroke survivors with tactile sensory deficits, using a repeated measures design. Sensory noise in the form of subthreshold, white noise, mechanical vibration was applied to the wrist skin during motor tasks. Hand dexterity assessed by the Nine Hole Peg Test and the Box and Block Test and pinch strength significantly improved when the sensory noise was turned on compared with when it was turned off in chronic stroke survivors. The subthreshold sensory noise to the wrist appears to induce improvements in hand motor function possibly via neuronal connections in the sensoriomotor cortex. The approach of applying concomitant, unperceivable mechanical vibration to the wrist during hand motor tasks is easily adoptable for clinic use as well as unsupervised home use. This pilot study suggests a potential for a wristband-type assistive device to complement hand rehabilitation for stroke survivors with sensorimotor deficit.

A shoe insole delivering subsensory vibratory noise improves balance and gait in healthy elderly people

OBJECTIVES

To test whether subsensory vibratory noise applied to the sole of the foot using a novel piezoelectric vibratory insole can significantly improve sensation, enhance balance, and reduce gait variability in elderly people, as well as to determine the optimal level of vibratory noise and whether the therapeutic effect would endure and the user's sensory threshold would remain constant during the course of a day.

DESIGN

A randomized, single-blind, crossover study of 3 subsensory noise stimulation levels on 3 days.

SETTING

Balance and gait laboratory.

PARTICIPANTS

Healthy community-dwelling elderly volunteers (N=12; age, 65-90y) who could feel the maximum insole vibration.

INTERVENTIONS

A urethane foam insole with the piezoelectric actuators delivering subsensory vibratory noise stimulation to the soles of the feet.

MAIN OUTCOME MEASURES

Balance, gait, and timed Up and Go (TUG) test.

RESULTS

The vibratory insoles significantly improved performance on the TUG test, reduced the area of postural sway, and reduced the temporal variability of walking at both 70% and 85% of the sensory threshold and during the course of a day. Vibratory sensation thresholds remained relatively stable within and across study days.

CONCLUSIONS

This study provides proof of concept that the application of the principle of stochastic resonance to the foot sole sensory system using a new low-voltage piezoelectric technology can improve measures of balance and gait that are associated with falls. Effective vibratory noise amplitudes range from 70% to 85% of the sensory threshold and can be set once daily.

Enhanced corticomuscular coherence by external stochastic noise

Noise can have beneficial effects as shown by the stochastic resonance (SR) phenomenon which is characterized by performance improvement when an optimal noise is added. Modern attempts to improve human performance utilize this phenomenon. The purpose of the present study was to investigate whether performance improvement by addition of optimum noise (ON) is related to increased cortical motor spectral power (SP) and increased corticomuscular coherence. Eight subjects performed a visuomotor task requiring to compensate with the right index finger a static force (SF) generated by a manipulandum on which Gaussian noise was applied. The finger position was displayed on-line on a monitor as a small white dot which the subjects had to maintain in the center of a green bigger circle. Electroencephalogram from the contralateral motor area, electromyogram from active muscles and finger position were recorded. The performance was measured by the mean absolute deviation (MAD) of the white dot from the zero position. ON compared to the zero noise condition induced an improvement in motor accuracy together with an enhancement of cortical motor SP and corticomuscular coherence in beta-range. These data suggest that the improved sensorimotor performance via SR is consistent with an increase in the cortical motor SP and in the corticomuscular coherence.

Broad-band Gaussian noise is most effective in improving motor performance and is most pleasant

Modern attempts to improve human performance focus on stochastic resonance (SR). SR is a phenomenon in non-linear systems characterized by a response increase of the system induced by a particular level of input noise. Recently, we reported that an optimum level of 0–15 Hz Gaussian noise applied to the human index finger improved static isometric force compensation. A possible explanation was a better sensorimotor integration caused by increase in sensitivity of peripheral receptors and/or of internal SR. The present study in 10 subjects compares SR effects in the performance of the same motor task and on pleasantness, by applying three Gaussian noises chosen on the sensitivity of the fingertip receptors (0–15 Hz mostly for Merkel receptors, 250–300 Hz for Pacini corpuscles and 0–300 Hz for all). We document that only the 0–300 Hz noise induced SR effect during the transitory phase of the task. In contrast, the motor performance was improved during the stationary phase for all three noise frequency bandwidths. This improvement was stronger for 0–300 Hz and 250–300 Hz than for 0–15 Hz noise. Further, we found higher degree of pleasantness for 0–300 Hz and 250–300 Hz noise bandwidths than for 0–15 Hz. Thus, we show that the most appropriate Gaussian noise that could be used in haptic gloves is the 0–300 Hz, as it improved motor performance during both stationary and transitory phases. In addition, this noise had the highest degree of pleasantness and thus reveals that the glabrous skin can also forward pleasant sensations.

Remote vibrotactile noise improves light touch sensation in stroke survivors' fingertips via stochastic resonance

Background and purpose

Stroke rehabilitation does not often integrate both sensory and motor recovery. While subthreshold noise was shown to enhance sensory signal detection at the site of noise application, having a noise-generating device at the fingertip to enhance fingertip sensation and potentially enhance dexterity for stroke survivors is impractical, since the device would interfere with object manipulation. This study determined if remote application of subthreshold vibrotactile noise (away from the fingertips) improves fingertip tactile sensation with potential to enhance dexterity for stroke survivors.

Methods

Index finger and thumb pad sensation was measured for ten stroke survivors with fingertip sensory deficit using the Semmes-Weinstein Monofilament and Two-Point Discrimination Tests. Sensation scores were measured with noise applied at one of three intensities (40%, 60%, 80% of the sensory threshold) to one of four locations of the paretic upper extremity (dorsal hand proximal to the index finger knuckle, dorsal hand proximal to the thumb knuckle, dorsal wrist, volar wrist) in a random order, as well as without noise at beginning (Pre) and end (Post) of the testing session.

Results

Vibrotactile noise of all intensities and locations instantaneously and significantly improved Monofilament scores of the index fingertip and thumb tip (p < .01). No significant effect of the noise was seen for the Two-Point Discrimination Test scores.

Conclusions

Remote application of subthreshold (imperceptible) vibrotactile noise at the wrist and dorsal hand instantaneously improved stroke survivors’ light touch sensation, independent of noise location and intensity. Vibrotactile noise at the wrist and dorsal hand may have enhanced the fingertips’ light touch sensation via stochastic resonance and interneuronal connections. While long-term benefits of noise in stroke patients warrants further investigation, this result demonstrates potential that a wearable device applying vibrotactile noise at the wrist could enhance sensation and grip ability without interfering with object manipulation in everyday tasks.

Necessity of noise in physiology and medicine

Noise is omnipresent in biomedical systems and signals. Conventional views assume that its presence is detrimental to systems' performance and accuracy. Hence, various analytic approaches and instrumentation have been designed to remove noise. On the contrary, recent contributions have shown that noise can play a beneficial role in biomedical systems. The results of this literature review indicate that noise is an essential part of biomedical systems and often plays a fundamental role in the performance of these systems. Furthermore, in preliminary work, noise has demonstrated therapeutic potential to alleviate the effects of various diseases. Further research into the role of noise and its applications in medicine is likely to lead to novel approaches to the treatment of diseases and prevention of disability.

A Systems Perspective on Postural and Gait Stability: Implications for Physical Activity in Aging and Disease

Postural instability, falls, and fear of falling that accompany frailty with aging and disease form major impediments to physical activity. In this article we present a theoretical framework that may help researchers and practitioners in the development and delivery of intervention programs aimed at reducing falls and improving postural stability and locomotion in older individuals and in those with disability due to disease. Based on a review of the dynamical and complex systems perspectives of movement coordination and control, we show that 1) central to developing a movement-based intervention program aimed at fall reduction and prevention is the notion that variability can play a functional role and facilitate movement adaptability, 2) intervention programs aimed at fall reduction should focus more on coordination and stability boundary measures instead of traditional gait and posture outcome variables, and 3) noise-based intervention techniques using stochastic resonance may offer external aids to improve dynamic balance control.

Improved sensorimotor performance via stochastic resonance

Several studies about noise-enhanced balance control in humans support the hypothesis that stochastic resonance can enhance the detection and transmission in sensorimotor system during a motor task. The purpose of the present study was to extend these findings in a simpler and controlled task. We explored whether a particular level of a mechanical Gaussian noise (0-15 Hz) applied on the index finger can improve the performance during compensation for a static force generated by a manipulandum. The finger position was displayed on a monitor as a small white point in the center of a gray circle. We considered a good performance when the subjects exhibited a low deviation from the center of this circle and when the performance had less variation over time. Several levels of mechanical noise were applied on the manipulandum. We compared the performance between zero noise (ZN), optimal noise (ON), and high noise (HN). In all subjects (8 of 8) the data disclosed an inverted U-like graph between the inverse of the mean variation in position and the input noise level. In other words, the mean variation was significantly smaller during ON than during ZN or HN. The findings suggest that the application of a tactile-proprioceptive noise can improve the stability in sensorimotor performance via stochastic resonance. Possible explanations for this improvement in motor precision are an increase of the peripheral receptors sensitivity and of the internal stochastic resonance, causing a better sensorimotor integration and an increase in corticomuscular synchronization.

The effects of rhythmic sensory cues on the temporal dynamics of human gait

Walking is a complex, rhythmic task performed by the locomotor system. However, natural gait rhythms can be influenced by metronomic auditory stimuli, a phenomenon of particular interest in neurological rehabilitation. In this paper, we examined the effects of aural, visual and tactile rhythmic cues on the temporal dynamics associated with human gait. Data were collected from fifteen healthy adults in two sessions. Each session consisted of five 15-minute trials. In the first trial of each session, participants walked at their preferred walking speed. In subsequent trials, participants were asked to walk to a metronomic beat, provided through visually, aurally, tactile or all three cues (simultaneously and in sync), the pace of which was set to the preferred walking speed of the first trial. Using the collected data, we extracted several parameters including: gait speed, mean stride interval, stride interval variability, scaling exponent and maximum Lyapunov exponent. The extracted parameters showed that rhythmic sensory cues affect the temporal dynamics of human gait. The auditory rhythmic cue had the greatest influence on the gait parameters, while the visual cue had no statistically significant effect on the scaling exponent. These results demonstrate that visual rhythmic cues could be considered as an alternative cueing modality in rehabilitation without concern of adversely altering the statistical persistence of walking.

Patterns of gait variability across the lifespan in persons with and without down syndrome

BACKGROUND AND PURPOSE

Greater gait variability has been observed in persons with Down syndrome (DS). An understanding of baseline patterns of variability, how these patterns relate to adaptive control of gait, and whether increasing or decreasing variability is better is necessary for physical therapists to determine whether and when to intervene. Our aim was to describe patterns of gait variability across the lifespan in persons with DS.

METHODS

We examined differences in patterns of gait variability in new walkers, preadolescents, and adults with DS and typical development (TD). We collected kinematic data, while participants walked on a treadmill, and analyzed the data using the nonlinear measures of Lyapunov Exponent (LyE) and Approximate Entropy (ApEn).

RESULTS

Beyond the greater gait variability demonstrated across the lifespan in persons with DS compared with their peers with TD, we report herein significant differences in nonlinear measures of patterns of variability. Preadolescents demonstrated higher LyE and ApEn values than new walkers and adults, suggesting that they are more adaptive in their use of variability during gait.

CONCLUSION

From a clinical perspective, our results suggest that it may be of value to focus interventions on increasing adaptive use of variability during gait in new walkers and adults with DS. Experience with increased variability through practice under variable conditions or with perturbations may improve adaptive use of variability during gait.

Baseline-dependent effect of noise-enhanced insoles on gait variability in healthy elderly walkers

The purpose of this study was to determine whether providing subsensory stochastic-resonance mechanical vibration to the foot soles of elderly walkers could decrease gait variability. In a randomized double-blind controlled trial, 29 subjects engaged in treadmill walking while wearing sandals customized with three actuators capable of producing stochastic-resonance mechanical vibration embedded in each sole. For each subject, we determined a subsensory level of vibration stimulation. After a 5-min acclimation period of walking with the footwear, subjects were asked to walk on the treadmill for six trials, each 30s long. Trials were pair-wise random: in three trials, actuators provided subsensory vibration; in the other trials, they did not. Subjects wore reflective markers to track body motion. Stochastic-resonance mechanical stimulation exhibited baseline-dependent effects on spatial stride-to-stride variability in gait, slightly increasing variability in subjects with least baseline variability and providing greater reductions in variability for subjects with greater baseline variability (p<.001). Thus, applying stochastic-resonance mechanical vibrations on the plantar surface of the foot reduces gait variability for subjects with more variable gait. Stochastic-resonance mechanical vibrations may provide an effective intervention for preventing falls in healthy elderly walkers.

Altering gait by way of stimulation of the plantar surface of the foot: the immediate effect of wearing textured insoles in older fallers

BACKGROUND

Evidence suggests that textured insoles can alter gait and standing balance by way of enhanced plantar tactile stimulation. However, to date, this has not been explored in older people at risk of falling. This study investigated the immediate effect of wearing textured insoles on gait and double-limb standing balance in older fallers.

METHODS

Thirty older adults >65 years (21 women, mean [SD] age 79.0 [7.1]), with self-reported history of ≥2 falls in the previous year, conducted tests of level-ground walking over 10 m (GAITRite system), and double-limb standing with eyes open and eyes closed over 30 seconds (Kistler force platform) under two conditions: wearing textured insoles (intervention) and smooth (control) insoles in their usual footwear.

RESULTS

Wearing textured insoles caused significantly lower gait velocity (P = 0.02), step length (P = 0.04) and stride length (P = 0.03) compared with wearing smooth insoles. No significant differences were found in any of the balance parameters (P > 0.05).

CONCLUSIONS

A textured insole worn by older adults with a history of falls significantly lowers gait velocity, step length and stride length, suggesting that this population may not have an immediate benefit from this type of intervention. The effects of prolonged wear remain to be investigated.

Changes in postural sway frequency and complexity in altered sensory environments following whole body vibrations

Studies assessing whole body vibration (WBV) have produced largely positive effects, with some neutral, on postural control with frequencies between 25 and 40 Hz. However no conclusive evidence indicates that 25-40 Hz elicits the optimal beneficial effects. To address this issue, a larger range of vibration intensity (10-50 Hz at peak-to-peak amplitudes of 2 and 5mm) was employed while increasing the postural complexity (altered somatosensory and/or visual information) to assess acute effects of 4-min of WBV on postural control. Twelve healthy young adults underwent postural assessment at four time intervals (prior to, immediately following and 10 and 20 min post WBV). Findings revealed both postural sway frequency and sway complexity/regularity were affected by WBV. Baseline posture demonstrated increased sway frequency (p=.04) following WBV with no changes in sway complexity. When the support surface was altered, changes in both the frequency and complexity of sway were elicited (p=.027, .002, respectively). When both somatosensory and visual information were altered delayed improvements in postural control were elicited (p=.05 and .01, for frequency and complexity, respectively). Given the differential acute effects as a function of postural task complexity, future longitudinal studies could determine the overall training effect on sway frequency and complexity.

The evaluation of walking footwear on postural stability in healthy older adults: an exploratory study

BACKGROUND

It has been proposed that walking footwear enhances postural stability in healthy older adults. The aim of the study is to evaluate differences between two different types of athletic footwear in relation to postural stability in healthy older adults.

METHODS

A convenience sample of 21 healthy older adults with mean (SD) of 74 (5) years was recruited. Postural stability was measured using a force plate for anterior-posterior (AP) and mediolateral (ML) centre of pressure excursion for 30s with eyes closed and open using two different types of athletic footwear. Each participant performed three repetitions of bipedal standing. Two-way analysis of variance tested the interaction effect of the footwear and eye conditions on anterior-posterior (AP) and mediolateral (ML) postural sway.

FINDINGS

There was no significant footwear-eye condition interaction for anterior-posterior(AP) postural sway but there were significant main effects for both the footwear and eye conditions (P<0.05). The significant main effects for the footwear conditions occurred between barefeet and the two shoe conditions, but not between the two shoe conditions. For mediolateral (ML) postural sway there was no significant interaction effect and no main effects for the footwear and eye conditions (P>0.05).

INTERPRETATION

The results suggest that older adults demonstrate an initial destabilisation effect which could possibly be of benefit to functional ability but the long-term effects of ability of athletic footwear to enhance postural stability requires further investigation.

Gait, gait variability and the risk of multiple incident falls in older people: a population-based study

BACKGROUND

it is uncertain as to which measures of gait best predict those who are likely to fall. Our aim was to investigate the associations of gait and gait variability measures with incident falls risk.

METHODS

individuals aged 60-86 years (n = 412) were randomly selected from the Tasmanian electoral roll. Average gait and gait variability measures were collected on a computerised walkway. Falls were recorded prospectively over 12 months. Log multinomial regression was used to estimate the relative risk of single and multiple falls associated with gait measures. Covariates included age, sex, sensorimotor and cognitive measures, mood and medications.

RESULTS

in this population-based study greater intra-individual variability in step length and double-support phase were linearly associated with increased risk of multiple falls (P = 0.04). Non-linear associations with multiple falls were found for gait speed P = 0.002, cadence P = 0.004 and step time variability P = 0.03. None of the gait measures predicted risk of single falls.

CONCLUSION

there is an increased risk of multiple falls, but not single falls, in older people with poorer gait. Specific measures of gait and gait variability seem to confer this risk and may be amenable to interventions designed to reduce the risk of multiple falls in older people.

The effects of enhanced plantar sensory feedback and foot orthoses on midfoot kinematics and lower leg neuromuscular activation

Excessive foot pronation has been associated with injuries of the lower extremity. No research has investigated the effect of enhancing plantar sensory feedback on foot pronation. The aim of this study was to determine whether a shoe with enhanced plantar sensory feedback reduces midfoot pronation. Midfoot kinematics and electromyography of the peroneus longus, tibialis anterior and medial gastrocnemius of 21 males (age: 21.0±4.0 years, height: 176.8±5.0 cm, mass: 73.3±6.5 kg) were recorded whilst walking in a neutral shoe, a neutral shoe with a prefabricated foot orthotic and a neutral shoe with nodules located on the plantar-medial insole (experimental shoe). Friedman's ANOVA and Wilcoxon tests were used to evaluate differences between shoe conditions. Mean midfoot-tibia angles during ground contact were significantly more supinated when wearing the experimental shoe (+7.14°, p=0.023) or orthotic (+3.83°, p=0.006) compared to the neutral shoe. During the loading phase, midfoot angles were significantly more supinated when wearing the experimental shoe compared to the orthotic (+5.53°, p=0.008) or neutral shoe (+6.20°, p=0.008). In the midstance phase, midfoot supination was significantly higher in the orthotic compared to the neutral shoe (+2.79°, p=0.006). Finally, supination was increased during the propulsive phase when wearing the experimental shoe compared to the orthotic (+7.43°, p=0.010) or neutral shoe (+10.83°, p=0.009). No significant (p<0.05) differences in muscle activation were observed. These results suggest that increasing plantar sensory feedback to the medial aspect of the foot reduces midfoot pronation during an acute bout of walking. Further work is needed to explore whether these effects remain over longer time periods.

Geriatric vestibulopathy assessment and management

PURPOSE OF REVIEW

This review discusses the demographics of dizziness in the older person, the evaluation of the older dizzy patient and how the treatment of dizziness in older patients differs from that in younger individuals.

RECENT FINDINGS

Seven percent of all visits to primary care physicians for patients older than 65 years of age are for dizziness, and dizziness is the most common complaint for patients older than 75 years. In a German study, the 12-month prevalence of vertigo in the general population was 5% with an incidence of 1.4% in adults overall. For individuals aged 60-69 the 12-month prevalence was found to be 7.2% and in individuals 70 years of age or older 8.9%. Data from the United States National Health and Nutrition Examination Surveys indicated that the prevalence of vestibular dysfunction for individuals in the seventh decade of life, eighth decade of life, and older was 49.4, 68.7, and 84.8 percent, respectively. Only subtle age effects are seen on caloric and rotational testing whereas vestibular evoked myogenic potentials (VEMPs) change somewhat with age. Particle repositioning for benign paroxysmal positional vertigo combined with vestibular rehabilitation is more effective than only performing the repositioning maneuver. Tai Chi appears to be an effective intervention for older adults at risk for falling.

SUMMARY

When caring for an older dizzy patient always assess medication use, perform a Dix-Hallpike maneuver, obtain orthostatic vital signs, discuss fall risk precautions, and consider referral for vestibular rehabilitation.

Re-interpreting detrended fluctuation analyses of stride-to-stride variability in human walking

Detrended fluctuation analyses (DFA) have been widely used to quantify stride-to-stride temporal correlations in human walking. However, significant questions remain about how to properly interpret these statistical properties physiologically. Here, we propose a simpler and more parsimonious interpretation than previously suggested. Seventeen young healthy adults walked on a motorized treadmill at each of 5 speeds. Time series of consecutive stride lengths (SL) and stride times (ST) were recorded. Time series of stride speeds were computed as SS=SL/ST. SL and ST exhibited strong statistical persistence (α≫0.5). However, SS consistently exhibited slightly anti-persistent (α<0.5) dynamics. We created three surrogate data sets to directly test specific hypotheses about possible control processes that might have generated these time series. Subjects did not choose consecutive SL and ST according to either independently uncorrelated or statistically independent auto-regressive moving-average (ARMA) processes. However, cross-correlated surrogates, which preserved both the auto-correlation and cross-correlation properties of the original SL and ST time series successfully replicated the means, standard deviations, and (within computational limits) DFA α exponents of all relevant gait variables. These results suggested that subjects controlled their movements according to a two-dimensional ARMA process that specifically sought to minimize stride-to-stride variations in walking speed (SS). This interpretation fully agrees with experimental findings and also with the basic definitions of statistical persistence and anti-persistence. Our findings emphasize the necessity of interpreting DFA α exponents within the context of the control processes involved and the inherent biomechanical and neuro-motor redundancies available.