James Niemi

Vibrating insoles and balance control in elderly people

Somatosensory function declines with age, and such changes have been associated with diminished motor performance. Input noise can enhance sensory and motor function. We asked young and elderly participants to stand quietly on vibrating gel-based insoles, and calculated sway parameters and random-walk variables. In our 27 participants, application of noise resulted in a reduction in seven of eight sway parameters in young participants and all of the sway variables in elderly participants. Elderly participants showed greater improvement than young people in two variables, mediolateral range (p=0.008), and critical mean square displacement (p=0.012). Noise-based devices, such as randomly vibrating insoles, could ameliorate age-related impairments in balance control.

Noise-enhanced balance control in patients with diabetes and patients with stroke

Somatosensory function declines with diabetic neuropathy and often with stroke, resulting in diminished motor performance. Recently, it has been shown that input noise can enhance human sensorimotor function. The goal of this study was to investigate whether subsensory mechanical noise applied to the soles of the feet via vibrating insoles can be used to improve quiet‐standing balance control in 15 patients with diabetic neuropathy and 15 patients with stroke. Sway data of 12 healthy elderly subjects from a previous study on vibrating insoles were added for comparison.

Noise-enhanced balance control in older adults.

Somatosensory information is critical to balance control and fall prevention in older adults. Recently, it has been shown that low-level input noise (electrical or mechanical) can enhance the sensitivity of the human somatosensory system. In this study, we tested the effect of low-level electrical noise, applied at the knee, on balance control in 13 healthy elderly volunteers. Subjects performed multiple single-legged stance trials with imperceptible electrical noise applied at the knee during half of the trials. Balance performance was characterized using a force platform to measure the displacement of the center of pressure (COP) under the subjects stance foot. Seven sway parameters were extracted from the COP time series. Improved balance was defined as a reduction in postural sway as indicated by decreases in the COP measures. Six of the seven sway parameters decreased with electrical noise. Three of these parameters decreased significantly (p < 0.05), and a fourth parameter was borderline significant. Averaged across subjects, the application of electrical noise resulted in a 3.8% reduction in mediolateral COP standard deviation (p = 0.04), a 5.4% decrease in the maximum anteroposterior COP excursion (p = 0.03), a 3.1% reduction in the COP path length (p = 0.04), and a 7.8% decrease in swept area (p = 0.05). The results suggest that imperceptible electrical noise, when applied to the knee, can enhance the balance performance of healthy older adults. These findings suggest that electrical noise-based devices may be effective in improving balance control in elderly people.

Noise-enhanced human sensorimotor function

We review our work on using input noise (mechanical and electrical, respectively) to enhance somatosensation in humans and improve the performance of the human balance control system. We also discuss bioengineering applications and future directions for stochastic resonance (SR) based techniques and devices. Age- and disease-related sensory loss may be reversible by exploiting SR-type effects.

Enhancing tactile sensation in older adults with electrical noise stimulation.

&NA; Older adults often suffer from diminished somatosensation stemming from age‐related neuropathy. Recently, localized low‐level electrical noise stimulation was shown to enhance tactile sensitivity in healthy young subjects. Here, we hypothesized that fine‐touch sensitivity in older adults can be similarly improved. Semmes‐Weinstein monofilaments were used to evaluate fine‐touch sensitivity on the first metatarsal phalangeal joint with four electrical stimulus conditions and a null (no‐noise) condition in nine healthy elderly subjects. Electrical noise stimulation resulted in a statistically significant increase in the number of detections below the null‐condition detection threshold, for five of the nine subjects, as well as across the entire population. This work suggests that electrical noise‐based techniques may enable people to overcome functional difficulties due to age‐related sensory loss.

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 users 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.

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.

Prolonged Mechanical Noise Restores Tactile Sense in Diabetic Neuropathic Patients

Acute application of stochastic resonance (SR), defined as a subsensory level of mechanical noise presented directly to sensory neurons, improves the vibration and tactile perception in diabetic patients with mild to moderate neuropathy. This study examined the effect of 1 hour of continuous SR stimulation on sensory nerve function. Twenty diabetic patients were studied. The effect of stimulation was measured at 2 time points, at the beginning and after 60 minutes of continual SR stimulation. This effect was measured using the vibration perception threshold (VPT) at the big toe under 2 conditions: a null (no SR) condition and active SR, defined as mechanical noise below the subjects own threshold of perception. The measurements under null and active conditions were done randomly and the examiner was blinded regarding the type of condition. Immediately after SR application, the VPT with SR in null condition was similar to baseline (32.2 ± 13.1, P = nonsignificant) but was significantly lower during active SR (27.4 ± 11.9) compared with both baseline (P = .018) and off position (P = .045). The 60 minutes VPT with active SR (28.7 ± 11.1) reached significance comparing the baseline when one outlier was removed from the analysis (P = .031). It may be concluded that SR for a continuous 60-minute period can sustain the VPT improvement in diabetic patients with moderate to severe neuropathy. These results permit the conclusion that there is no short-term adaptation to the stimulation signal. Long-term application of this technique, perhaps in the form of a continually vibrating shoe insert, or insole, may result in sustained improvement of nerve function.

Sensory enhancing insoles improve athletic performance during a hexagonal agility task

Athletes incorporate afferent signals from the mechanoreceptors of their plantar feet to provide information about posture, stability, and joint position. Sub-threshold stochastic resonance (SR) sensory enhancing insoles have been shown to improve balance and proprioception in young and elderly participant populations. Balance and proprioception are correlated with improved athletic performance, such as agility. Agility is defined as the ability to quickly change direction. An athletes agility is commonly evaluated during athletic performance testing to assess their ability to participate in a competitive sporting event. Therefore, the purpose of this study was to examine the effects of SR insoles during a hexagonal agility task routinely used by coaches and sports scientists. Twenty recreational athletes were recruited to participate in this study. Each athlete was asked to perform a set of hexagonal agility trials while SR stimulation was either on or off. Vicon motion capture was used to measure feet position during six successful trials for each stimulation condition. Stimulation condition was randomized in a pairwise fashion. The study outcome measures were the task completion time and the positional accuracy of footfalls. Pairwise comparisons revealed a 0.12s decrease in task completion time (p=0.02) with no change in hopping accuracy (p=0.99) when SR stimulation was on. This is the first study to show athletic performance benefits while wearing proprioception and balance improving equipment on healthy participants. With further development, a self-contained sensory enhancing insole device could be used by recreational and professional athletes to improve movements that require rapid changes in direction.

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 participants 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.