Whole body vibration training reduces plantar foot sensitivity but improves balance control of healthy subjects

The goal of this study was to investigate the effects of short-time whole body vibration (WBV) training on foot vibration sensitivity of healthy subjects. Furthermore, the effects of WBV on a balance task (one-leg stand) were also evaluated. 30 young healthy subjects participated in the study. Vibration perception thresholds and balance were measured prior and after a single session of a 4-min WBV training (27 Hz, 2 mm horizontal amplitude). Thresholds were measured at 200 Hz at three anatomical locations of the plantar foot area (first and fifth metatarsal heads and heel). Body balance was quantified using the length as well as the area described by the center of pressure (COP) at quiet, one-leg standing. Whereas vibration thresholds significantly increased after WBV training at all measured locations, there was a significant decrease in the balance related parameters after WBV exercise. The results indicate that the above-threshold, sinusoidal vibration used during WBV training is not an adequate strategy to stimulate/improve vibration sensitivity. The improvements seen in balance after WBV are likely to have neuromuscular mechanisms as their main component rather than increased foot sensitivity.     

Location specificity of plantar cutaneous reflexes involving lower limb muscles in humans

It is known that cutaneous reflexes in human hand muscles show strong location-specificity dependent on the digit stimulated. We hypothesized that in lower leg muscles the cutaneous reflex following tactile sensation of the plantar surface of the foot is also organized in a location-specific manner. The purpose of the present study was to test this hypothesis. Middle latency reflexes (∼70–110 ms, MLR) following non-noxious electrical stimulation to different locations on the plantar foot were recorded from 16 neurologically intact volunteers (15 males, 1 female). Electrical stimulation was given to the fore-medial (f-M), fore-lateral (f-L) and heel (HL) regions of the plantar surface of the right foot while the subjects performed isometric dorsiflexion (tibialis anterior, TA), plantarflexion (soleus, Sol and medial gastrocnemius, MG), eversion (peroneus longus, PL) and knee extension (vastus lateralis, VL) while sitting and standing. In the Sol and MG, an excitatory response was observed following HL stimulation, which was switched to an inhibitory response following f-M or f-L stimulation (P < 0.001). A reciprocal pattern in contrast to Sol was observed in the TA. In the PL, MLR exhibited significant excitation following both f-L and HL stimulation, which, however, was switched to an inhibitory response following f-M stimulation (P < 0.001). Moderate inhibition of the MLR was seen in the VL for all stimulated positions. Systematic stimulation along the lateral side of the plantar foot demonstrated that the reflex reversal occurred around the middle of the plantar foot in the Sol and TA. In all muscles tested, the slope of the regression line between the magnitude of the MLR and background electromyographic activity significantly decreased during standing compared with sitting except for the PL following f-L simulation. These results suggest that reflex effects from cutaneous nerves in the plantar foot onto the motoneurons innervating the lower leg muscles are organized in a highly topographic manner in humans. The organization of these reflexes may play an important role in the alteration of limb loading and/or ground contact in response to tactile sensation of the plantar foot while sitting and standing.     

Mechanical sensibility of the sole of the foot determined with vibratory stimuli of varying frequency

Summary The mechanoreceptive properties of the sole of the foot were determined by measuring the detection thresholds to vibratory stimuli of 20, 80, and 240 Hz frequency and 300 ms duration. The thresholds were measured at six different sites on the left sole and at toes 1 and 3 with probes of 2 and 8 mm diameter connected to the moving coil of an electromechanical vibrator. The subject sat in an armchair during the experiments, with the left leg supported horizontally by a vacuum cast positioned on a table. Six subjects participated in the experiments. A simple method of limits was used to make the measurements. Lower average thresholds were obtained with higher vibration frequencies, the average thresholds varying between 40–90 m at 20 Hz and well below 10 m at 240 Hz. The major decrease in thresholds occurred between 20 and 80 Hz. Interindividual variability in thresholds was large, but the threshold curves obtained from different subjects and from different stimulation points were of the same general shape. The highest thresholds were measured from the toes, but this regional difference in sensibility was obtained only at the higher vibration frequencies. Comparison of the threshold values at the sole with those found with similar stimuli at the thenar eminence and middle fingertip indicates that the mechanoreceptor mechanisms transmitting information about low-frequency vibration in the sole are similar to those in the palmar skin of the hand.     

部分足截肢部位对步态的影响

目的 部分足截肢是临床截肢手术中最常见的截肢类型,跖趾关节部位、跖骨部位和Lisfrane关节部位是PFA最典型的三种截肢平面,分析经这些平面的部分足截肢对步态的影响,将有助于相关辅具的设计和评价。方法 采用Footscan平板式足底压力测试系统和Optotrak三维运动分析系统,以跨步长、步频、步速、足底各区域的峰值压力、冲量、接触时间、接触面积为特征参量,对这三种截肢平面患者进行了步态分析。结果 分析结果表明,三种不同足部截肢平面中,残足越短,跨步长越小,双足承重时间差越明显;MTP的峰值压力主要在跖骨处和足跟处,TMA和Lisfrane的峰值压力集中在足中部和足跟处。结论 推断在设计和评价不同足部截肢平面的相关辅具时,不同截肢平面辅具有相应差异。     

Effects of footwear on plantar foot sensitivity: a study with Formula 1 shoes

The aim of this study was to investigate the influence of Formula 1 footwear on the ability of the plantar foot to detect vibration stimuli. Twenty-five male subjects participated in the study. Five foot/shoe conditions were analysed (barefoot and four shoe conditions). Vibration thresholds were measured at three anatomical locations of the plantar foot (heel, first metatarsal head and hallux) at two frequencies (30 and 200 Hz). The results show a frequency-dependent influence of footwear on foot sensitivity. The comparison between barefoot and shod conditions showed lower thresholds (P < 0.01) for the barefoot condition at 30 Hz, whereas lower thresholds (P < 0.01) were found for all shoe conditions at 200 Hz compared to barefoot. Lower thresholds (P < 0.01) were measured at 200 Hz in comparison to 30 Hz in all experimental conditions. The shoe outsole material seems to facilitate the transmission of high-frequent vibration stimuli to the skin, resulting in better vibration sensitivity at 200 Hz when wearing Formula 1 shoes compared to barefoot.     

无症状扁平足与正常足的足底压力和足弓形态对比研究

目的　通过与正常足青年女性对比分析得出无症状扁平足足底压力和足弓形态的特征。 方法　利用Zebris足底压力测量仪对正常足组（12例）和扁平足组（12例）进行直立状态和行走状态下的足底压力测试,并拍摄其负重位和非负重位的侧位X线片进行足弓形态测量,测量数据进行统计学分析。 结果 双足直立时,扁平足组与正常足组的足底压力差异无显著意义（P>0.05）;单足直立时,扁平足组的前足负重比例增大;步行时,扁平足组与正常足组足底压力中心运动轨迹有明显区别。扁平足组负重位与非负重位的足弓形态各参数有显著差异（P<0.05）,而且扁平足组负重位与正常足组负重位的足弓形态有显著差异（P<0.05）。 结论 无症状扁平足单足直立和行走状态的足底压力和足弓形态与正常足相比有明显区别,为评价、诊断和预防无症状扁平足提供定量化数据。     

自然行走对人体足底压力与下肢表面肌电信号影响的研究

目的 探究自然行走对正常人足底压力与下肢肌肉表面肌电信号(sEMG)的影响.方法 分别测量28例健康青年男性受试者在30 min平地自然行走前后足底压力与下肢肌肉的sEMG,得到行走前后峰值压强、冲量等足底压力参数及胫骨前肌、腓肠肌、股直肌与股二头肌的表面肌电时域参数积分肌电(iEMG)和频域参数平均功率频率(MPF),并检验峰值压强与身高、体质量的相关性.结果 平地自然行走开始时和30 min后,其左、右侧的峰值压强、冲量等各特征参数的差异均有统计学意义(均P＜0.05),不同参数的左、右侧差异分别体现在足底不同区域,而在跖骨区M3、M4、M5处各参数均表现出左侧大于右侧;行走前后左侧胫骨前肌、腓肠肌、骨直肌与股二头肌sEMG的iEMG均大于右侧;行走前后左侧胫骨前肌、腓肠肌的MPF大于右侧,其差异具有统计学意义(P＜0.05).30 min行走后右足脚趾区Toe2-5的峰值压强降低,其差异具有统计学意义(P＜0.05);各肌肉表面肌电iEMG无显著性变化,左侧股直肌的表面肌电信号的MPF显著性下降;峰值压强与身高、体质量均呈弱相关.结论 正常人自然行走中,足底压力和下肢表面肌电均具有左右侧的差异;30 min自然行走尚未导致足底压力出现明显疲劳状态的相应结果,因此自然行走30 min可维持步态的稳定性;30 min行走将导致左侧股直肌出现疲劳.     

Controlling posture using a plantar pressure-based,tongue-placed tactile biofeedback system

The present paper introduces an original biofeedback system for improving human balance control, whose underlying principle consists in providing additional sensory information related to foot sole pressure distribution to the user through a tongue-placed tactile output device. To assess the effect of this biofeedback system on postural control during quiet standing, ten young healthy adults were asked to stand as immobile as possible with their eyes closed in two conditions of No-biofeedback and Biofeedback. Centre of foot pressure (CoP) displacements were recorded using a force platform. Results showed reduced CoP displacements in the Biofeedback relative to the No-biofeedback condition. The present findings evidenced the ability of the central nervous system to efficiently integrate an artificial plantar-based, tongue-placed tactile biofeedback for controlling control posture during quiet standing.     

Influence of patellofemoral pain syndrome on plantar pressure in the foot rollover process during gait

BACKGROUND:

Patellofemoral Pain Syndrome is one of the most common knee disorders among physically active young women. Despite its high incidence, the multifactorial etiology of this disorder is not fully understood.

OBJECTIVES:

To investigate the influence of Patellofemoral Pain Syndrome on plantar pressure distribution during the foot rollover process (i.e., the initial heel contact, midstance and propulsion phases) of the gait.

MATERIALS AND METHODS:

Fifty-seven young adults, including 22 subjects with Patellofemoral Pain Syndrome (30 ± 7 years, 165 ± 9 cm, 63 ± 12 kg) and 35 control subjects (29 ± 7 years, 164 ± 8 cm, 60 ± 11 kg), volunteered for the study. The contact area and peak pressure were evaluated using the Pedar-X system (Novel, Germany) synchronized with ankle sagittal kinematics.

RESULTS:

Subjects with Patellofemoral Pain Syndrome showed a larger contact area over the medial (p = 0.004) and central (p = 0.002) rearfoot at the initial contact phase and a lower peak pressure over the medial forefoot (p = 0.033) during propulsion when compared with control subjects.

CONCLUSIONS:

Patellofemoral Pain Syndrome is related to a foot rollover pattern that is medially directed at the rearfoot during initial heel contact and laterally directed at the forefoot during propulsion. These detected alterations in the foot rollover process during gait may be used to develop clinical interventions using insoles, taping and therapeutic exercise to rehabilitate this dysfunction.     

足部三维有限元建模方法及其生物力学应用

目的探讨建立足部三维有限元模型的方法,应用模型模拟分析研究鞋垫设计参数,不同软组织刚度和受力情况下对足部的生物力学影响。方法建立基于解剖结构,包括软组织,韧带和腱膜,考虑材料的非线性和关节接触的足部三维有限元模型。有限元模型的可靠性利用模拟足踝关节在不同病理、手术和鞋垫矫治情况下的生物力学反应来验证。结果有限元分析结果表明,定制型鞋垫的形状比鞋垫材料的刚度对减少足底最大压力有更重要影响。软组织刚度的增加引起足底接触面积的减小,从而会导致足底跖骨区最大压力增加。部分和完全松解足底腱膜都会降低足弓高度,并增加足底韧带的张力和增加中足和跖骨的应力。体重增加和跟腱拉力增加都将成倍足底筋膜的拉力。结论所建足部有限元模型能预测足底压力分布和足内部骨骼软组织应力、应变情况,可以成为设计鞋垫和研究足部各种临床状况提供有力的分析工具。     

Multi-plug insole design to reduce peak plantar pressure on the diabetic foot during walking

There is evidence that appropriate footwear is an important factor in the prevention of foot pain in otherwise healthy people or foot ulcers in people with diabetes and peripheral neuropathy. A standard care for reducing forefoot plantar pressure is the utilization of orthotic devices such as total contact inserts (TCI) with therapeutic footwear. Most neuropathic ulcers occur under the metatarsal heads, and foot deformity combined with high localized plantar pressure, appear to be the most significant factors contributing to these ulcers. In this study, patient-specific finite element models of the second ray of the foot were developed to study the influence of TCI design on peak plantar pressure (PPP) under the metatarsal heads. A typical full contact insert was modified based on the results of finite element analyses, by inserting 4 mm diameter cylindrical plugs of softer material in the regions of high pressure. Validation of the numerical model was addressed by comparing the numerical results obtained by the finite element method with measured pressure distribution in the region of the metatarsal heads for a shoe and TCI condition. Two subjects, one with a history of forefoot pain and one with diabetes and peripheral neuropathy, were tested in the laboratory while wearing therapeutic shoes and customized inserts. The study showed that customized inserts with softer plugs distributed throughout the regions of high plantar pressure reduced the PPP over that of the TCI alone. This supports the outcome as predicted by the numerical model, without causing edge effects as reported by other investigators using different plug designs, and provides a greater degree of flexibility for customizing orthotic devices than current practice allows.     

Group II excitations from plantar foot muscles to human leg and thigh motoneurones

Projections of group II afferents from intrinsic foot muscles to lower limb motoneurones were investigated in humans after electrical stimuli were applied to the tibial nerve (TN) at ankle level, using modulation of the quadriceps H reflex, on-going EMG of the quadriceps and peroneus brevis, and PSTHs of single quadriceps, biceps, semitendinosus, tibialis anterior, and peroneus brevis motor units. TN stimulation evoked late and high-threshold excitation in all leg and thigh muscles investigated. The mean latency of the late excitation was 13.5+/-0.4 ms longer than that of the heteronymous monosynaptic Ia excitation, and the more caudal the motor nucleus the longer the central delay of the late effect, suggesting mediation through interneurones located rostral to motoneurones. The electrical threshold and conduction velocity of the largest diameter fibres evoking the late excitation were estimated to be approximately 2 and 0.67 times, respectively, those of the fastest Ia afferents, i.e. consistent with a mediation by group II afferents. Stimulation of the skin areas innervated by TN did not evoke late excitations. Further support for mediation through group II afferents was provided by the findings that: 1. the latency of the TN-induced late and high-threshold excitation in Per brev units was more delayed by cooling the nerve than that of the excitation evoked by group I afferents, and 2. tizanidine intake (known to depress selectively transmission of group II effects) suppressed the TN-induced late and high-threshold excitation whereas the group I facilitation was not modified.     

足底软组织硬化对足部生物力学影响的三维有限元分析

目的 通过有限元方法来研究足底软组织整体硬化以及跖骨头和跟骨下方软组织局部硬化对人体足踝系统的力学影响。方法 基于健康志愿者右足的核磁共振扫描图片建立足部三维有限元模型,通过改变足底软组织的生物力学属性和人体平衡站立位时的计算仿真来分析足底软组织的生物力学问题。同时,对此志愿者进行足底压力测试来验证模型的有效性。结果 建立足踝有限元模型得到了有效的验证并完成了不同软组织属性定义下站立位的运算;在平衡站立位时足底接触压力分布状况和足踝内部一些软、硬组织的受力情况得到量化。结论 软组织硬化,特别是跖骨头和跟骨下方软组织局部硬化,对足底受压接触面积、压力峰值以及足底软组织垫所受的应力等产生了明显影响,大大增加了糖尿病患者发生足底溃烂的可能性。     

Inter-individual variability in sensory weighting of a plantar pressure-based, tongue-placed tactile biofeedback for controlling posture

The purpose of the present experiment was to investigate whether the sensory weighting of a plantar pressure-based, tongue-placed tactile biofeedback for controlling posture could be subject to inter-individual variability. To achieve this goal, 60 young healthy adults were asked to stand as immobile as possible with their eyes closed in two conditions of No-biofeedback and Biofeedback. Centre of foot pressure (CoP) displacements were recorded using a force platform. Overall, results showed reduced CoP displacements in the Biofeedback relative to the No-biofeedback condition, evidencing the ability of the central nervous system to efficiently integrate an artificial plantar-based, tongue-placed tactile biofeedback for controlling posture during quiet standing. Results further showed a significant positive correlation between the CoP displacements measured in the No-biofeedback condition and the decrease in the CoP displacements induced by the use of the biofeedback. In other words, the degree of postural stabilization appeared to depend on each subject's balance control capabilities, the biofeedback yielding a greater stabilizing effect in subjects exhibiting the largest CoP displacements when standing in the No-biofeedback condition. On the whole, by evidencing a significant inter-individual variability in sensory weighting of an additional tactile information related to foot sole pressure distribution for controlling posture, the present findings underscore the need and the necessity to address the issue of inter-individual variability in the field of neuroscience.     

清醒健康志愿者短暂肢体缺血的可接受性和安全性评价

目的: 评估清醒健康志愿者短暂肢体缺血的安全性和可接受性。方法: 选择60名20-30岁健康志愿者,男女各半,利用血压计袖带的充气/放气进行3个循环的非优势上肢缺血再灌注,每个循环为缺血5 min/再灌注5 min,充气压力为200 mmHg。此过程中持续监测心率、血压、脉搏氧饱和度等生命体征,操作结束后用调查问卷(主要以0-10分的数字评分法为量化尺度)评估可接受性和不适感觉,于第3 d重复进行1次同样的问卷调查,以评估问卷的可信度,保证结果的可靠性。结果: 短暂肢体缺血中,志愿者的心率、血压和脉搏氧饱和度均波动在正常范围内。56.6%男性和66.7%女性的可接受度为7-8分,56.7%志愿者的舒适程度在4-6分,86.7%志愿者认为麻木感是最主要的不适感觉,46.6%男性和50.9%女性的麻木感评分在7-8分,每个循环肢体缺血中麻木感持续2-5 min,再灌注后1-2 min消失。男女间的可接受度和不适感觉无显著差异。问卷具有良好的重测信度(组内相关系数为0.990)。结论: 短暂肢体缺血是一种乐于被清醒健康志愿者所接受的、安全的远程缺血处理方法。     

How a plantar pressure-based,tongue-placed tactile biofeedback modifies postural control mechanisms during quiet standing

The purpose of the present study was to determine the effects of a plantar pressure-based, tongue-placed tactile biofeedback on postural control mechanisms during quiet standing. To this aim, 16 young healthy adults were asked to stand as immobile as possible with their eyes closed in two conditions of No-biofeedback and Biofeedback. Centre of foot pressure (CoP) displacements, recorded using a force platform, were used to compute the horizontal displacements of the vertical projection of the centre of gravity (CoG _v ) and those of the difference between the CoP and the vertical projection of the CoG (CoP-CoG _v ). Analysis of the CoP-CoG _v displacements showed larger root mean square (RMS) and mean power frequencies (MPF) in the Biofeedback than in the No-biofeedback condition. Stabilogram-diffusion analysis further showed a concomitant increased spatial and reduced temporal transition point co-ordinates at which the corrective processes were initiated and an increased persistent behaviour of the CoP-CoG _v displacements over the short-term region. Analysis of the CoG _v displacements showed decreased RMS and increased MPF in the Biofeedback relative to the No-biofeedback condition. Stabilogram-diffusion analysis further indicated that these effects mainly stem from reduced spatio-temporal transition point co-ordinates at which the corrective process involving CoG _v displacements is initiated and an increased anti-persistent behaviour of the CoG _v displacements over the long-term region. Altogether, the present findings suggest that the main way the plantar pressure-based, tongue-placed tactile biofeedback improves postural control during quiet standing is via both a reduction of the correction thresholds and an increased efficiency of the corrective mechanism involving the CoG _v displacements.     

BMP7 reduces synergistic injury induced by methamphetamine and ischemia in mouse brain

Previous studies have indicated that methamphetamine (MA) potentiates neurodegeneration induced by ischemia in brain. We, and others, have reported that bone morphogenetic protein 7 (BMP7) is protective against MA and ischemic brain injury. The purpose of this study is to examine whether BMP7 reduces synergistic injury induced by both MA and cerebral ischemia. Adult CD-1 mice were treated with MA (4x 10mg/kg, each dose 2h apart) or saline. Using the quantitative real time polymerase chain reaction, we found that MA suppressed the expression of BMP7 mRNA in the cerebral cortex 1 day after injection. Ischemic and reperfusional injuries were introduced by ligation of the right middle cerebral artery for 90min after MA injection. Animals were sacrificed for caspase-3/7 activity assay and tri-phenyl-tetrazolium chloride staining at 1h and 2 days after reperfusion, respectively. Cerebral infarction and caspase-3/7 activity were enhanced in the stroke animals pretreated with MA; both responses were attenuated by pretreatment with BMP7. In conclusion, our data suggest that MA facilitates cerebral infarction after ischemia possibly mediated, in part, through the suppression of BMP7.     

An MRI compatible loading device for the reconstruction of clinically relevant plantar pressure distributions and loading scenarios of the forefoot

The purpose of this study is to demonstrate a new MRI compatible loading device capable of reconstructing realistic loading scenarios of the human foot for research in the field of foot biomechanics. This device has two different configurations: one used to compress the forefoot and one to bend the metatarsophalangeal joints. Required plantar pressure distribution under the metatarsal heads can be achieved by modifying the distribution of the dorsally applied forces. To validate the device, subject-specific plantar pressures were measured and then reconstructed using the device. For quiet stance the peak pressure reconstruction error was 3% while for mid-stance phase of gait it was 8%. The device was also used to measure the passive bending stiffness of the metatarsophalangeal joints of one subject with low intra-subject variability. A series of preliminary MRI scans confirmed that the loading device can be used to produce static weight-bearing images of the foot (voxel size: 0.23 mm × 0.23 mm × 1.00 mm).The results indicate that the device presented here can accurately reconstruct subject specific plantar pressure distributions and measure the foot's metatarsophalangeal passive stiffness. Possible future applications include the validation of finite element models, the investigation of the relationship between plantar pressure and internal stresses/strains and the study of the foot's inter-segmental passive stiffness.