基于足底压力和关节运动信息的步态检测系统设计

作为老年人高发疾病,脑卒中有着较高的几率造成患者行动障碍。及时检测、获取偏瘫患者行走时步态信息,是治疗师为患者制定康复计划的重要环节。目前,较新的步态检测系统大多采用三维分析,三维步态分析系统体积较大、成本高、操作不便,在患者主动康复训练中存在较大的局限。针对现今步态检测系统的局限,设计了一种结合无线传输技术,检测患者关节运动角度及足底压力的运动信息检测系统。系统采用薄膜压力传感器、惯性传感器分别采集足底压力及关节运动信息,实现了对患者的8路足底压力信息及下肢关节运动角度信息的快速、有效采集。实验表明,系统可以有效采集关节运动角度及足底压力信息,在未来的康复训练中有着很好的应用前景。     

结合无符号Laplace谱特征的触觉步态识别算法

针对单纯利用压力点分布特征进行触觉步态识别的不足,提出了一种结合无符号Laplace谱特征的动态触觉步态识别算法。利用足底压力数字化场地采集常速、快速和慢速三种情况下的触觉步态数据,生成足底压力分布图像,并根据足底解剖学的结构划分区域;以足底压力图像各区域为节点构造结构图,并采用无符号Laplace矩阵表示;通过对该矩阵进行奇异值分解（Singular Value Decomposition,SVD）获取谱特征,并结合形状特征得到触觉步态特征;选择“一对一”的支持向量机（Support Vector Machine,SVM）多分类方法,按照人在行走过程中不同的速度分别构造分类器,从而实现动态触觉步态的识别。实验结果表明该识别算法对不同速度样本数据的触觉步态识别正确率都较高。     

基于步态检测算法的辅助行走系统设计

为了保证盲人和视障患者安全方便出行和减少误报警,设计一种基于步态检测算法的辅助行走系统。信号处理算法上利用小波包对信号进行降噪,提取三轴加速度的均值、标准差、方差与小波能量谱,并结合足底压力信息组成多维参数作为步态特征,选取基于遗传算法优化支持向量机进行步态识别。硬件部分主要包括三轴加速度信号和足底压力信号采集硬件设计。软件部分主要包括对足底压力信号和三轴加速度信号的采集和处理以及一款能够自动拨号安卓手机APP。实验结果表明,该系统基于多传感器融合的步态检测技术,步态检测识别率平均达90.48%。该系统便携性好、功耗低、测障效果好,在辅助行走领域具有一定的研究意义和实用价值。     

Wheeled assistive device for load carriage – the effects on human gait and biomechanics

Abstract

Soldiers are often required to carry loads which impose biomechanical strain on the human body. This can adversely affect physical performances. Recently, wheel-based devices (WBD) were designed to reduce the load on the soldier. In the present study, a prototype of this newly developed WBD was evaluated. Thirteen volunteers performed three exercise protocols on a treadmill as follows: (1) no load; (2) carrying 40% of their bodyweight with a backpack or; (3) with the WBD. Data acquisition included: gait parameters, vertical ground reaction forces (VGRF) and contact pressure acting on the shoulder. Biomechanical analysis showed that the WBD decreased the contact pressure on the shoulder and the VGRF. However, greater gait variability, in terms of cycle-to-cycle gait line generation, was observed, which might point to a difficulty in maintaining stability while walking. The study suggests that WBD has a potential to reduce the biomechanical strain on the soldier while carrying heavy loads. Future potential adjustments for the development of a better WBD-based solution are suggested.

Practitioner Summary: The present research observed the potential biomechanical advantages of using a wheel-based device designed to reduce the load on the soldier. It contributed to a lower mechanical force on the soldier’s body, yet causing modulations in gait control. Future design adjustments should be made to optimise the platform.     

Slips and falls in a cold climate: underfoot surface, footwear design and worker preferences for preventive measures

Slips and falls and associated outdoor injuries are prevalent in cold climates. The objectives of this field investigation were to describe the consequences of slips and falls on ice and snow and the associated injuries, to assess the risks of various icy and snowy surfaces, to identify design needs of footwear, and to ascertain preventive measure preferences of outdoor workers. The organizations investigated were a newspaper delivery service, a military regiment, mining and construction industries. The results showed that fall events occur most frequently on ice covered with snow. This is due to the difficulty of perceiving hidden risks in order to adjust gait strategies. The professional footwear provided does not provide enough protection against slips and falls. Slip resistant properties are ranked as one of the top requirements by the users. Their most preferred preventive measures are footwear with anti-slip properties and the application of anti-slip materials, such as sand or salt.     

Falls in the healthy elderly: predisposing causes

One hundred healthy men and women aged 65-85 took part in a prospective study. They were clinically examined and underwent laboratory tests of gait, balance and reaction time at the start of an observation year.

All falls occurring in that year were analysed in detail. Three-quarters of them were trips or slips; however, ten personal factors were identified which, if present, increased the likelihood of a fall occurring. These were: disturbance of gait following a rest period accompanied by a lighting change (in persons aged 70 and over); an absent or abnormal plantar reflex; failure to wear prescribed spectacles; the presence of anxiety/depression, of a foot problem, or of two or more self-perceived limitations on mobility; a history of former wearing of high heels; a sustained drop in pulse pressure 5 min after cessation of a rest period; restricted neck movements; and the presence of an inverse Romberg ratio.

The number of circumstantial and personal factors contributing to the falls varied between three and twelve.     

Biomechanics of slips

The biomechanics of slips are an important component in the prevention of fall-related injuries. The purpose of this paper is to review the available literature on the biomechanics of gait relevant to slips. This knowledge can be used to develop slip resistance testing methodologies and to determine critical differences in human behaviour between slips leading to recovery and those resulting in falls. Ground reaction forces at the shoe-floor interface have been extensively studied and are probably the most critical biomechanical factor in slips. The ratio of the shear to normal foot forces generated during gait, known as the required coefficient of friction (RCOF) during normal locomotion on dry surfaces or ‘friction used/achievable’ during slips, has been one biomechanical variable most closely associated with the measured frictional properties of the shoe/floor interface (usually the coefficient of friction or COF). Other biomechanical factors that also play an important role are the kinematics of the foot at heel contact and human responses to slipping perturbations, often evident in the moments generated at the lower extremity joints and postural adaptations. In addition, it must be realized that the biomechanics are dependent upon the capabilities of the postural control system, the mental set of the individual, and the perception of the environment, particularly, the danger of slipping. The focus of this paper is to review what is known regarding the kinematics and kinetics of walking on surfaces under a variety of environmental conditions. Finally, we discuss future biomechanical research needs to help to improve walkway-friction measurements and safety.     

基于线结构光和足底扫描的足部参数测量研究

针对现有足部轮廓三维重构方法精度低,鲁棒性差,成本昂贵且不符合实际足部生物力学研究要求等问题,设计了一种利用光学测量技术实现无接触式足部参数测量的系统。该系统一方面通过对足底扫描图像处理,构建足底轮廓点云,分割足底压力区域,计算足底相关参数;另一方面利用线结构光技术,重构足面轮廓,将足底轮廓点云与足面轮廓点云在系统规定世界坐标系内融合,形成完整足部轮廓点云,根据定义计算足部围度等足部系列参数。通过搭建相应硬件平台对多组人体足部进行测量,实验结果表明系统能够快速、精确地完成足部三维重构,具有很好的鲁棒性。     

Measurement of slipperiness: fundamental concepts and definitions

The main objective of this paper is to give an overview of basic concepts and definitions of terms related to the ‘measurement of slipperiness’ from the onset of a foot slide to a gradual loss of balance and a fall. Other unforeseen events prior to falls (e.g. tripping) are sparingly dealt with. The measurement of slipperiness may simply comprise an estimation of slipping hazard exposures that initiate the chain of events ultimately causing an injury. However, there is also a need to consider the human capacity to anticipate slipperiness and adapt to unsafe environments for avoiding a loss of balance and an injury. Biomechanical and human-centred measurements may be utilized for such an approach, including an evaluation of relevant safety criteria for slip/fall avoidance and procedures for validation of slip test devices. Mechanical slip testing approaches have been readily utilized to measure slipperiness in terms of friction or slip resistance but with conflicting outcomes. An improved understanding of the measurement of slipperiness paradigm seems to involve an integration of the methodologies used in several disciplines, among others, injury epidemiology, psychophysics, biomechanics, motor control, materials science and tribology.     

Preventing falls from roofs: a critical review

Work-related falls from roofs remain a significant problem for workers in the construction industry. Knowledge about the main causative or initiating factors leading to fall incidents is desperately needed for fall prevention intervention. From biomechanical and psychophysiological perspectives the majority of occupational falls, including falls from roofs, can be regarded as loss-of-balance incidents. The primary objective of this paper is to summarize the current knowledge from multiple fields about factors that are related to the control of balance during roofing work. An extensive literature review identified a number of environmental, task-related and personal factors that degrade the control of balance and could be associated with the initiation of falls from roofs. These factors include visual exposure to elevation; unstable visual cues and inadequate visual information in the work environment; ‘confined’ and inclined support surfaces; unexpected changes in roof surface properties; load handling; physical exertion; fatigue; task complexity that diverts workers' attention; individual differences; work experience and training; and personal protective equipment. Current measures to reduce falls from roofs focus mainly on fall protection procedures, such as the use of covers, guardrails, safety nets, and personal fall arrest systems, or the application of warning-line systems, safety monitoring systems, and fall protection plans. In many instances, these procedures are not practical for the industry and current regulations allow the use of alternative means of fall protection, such as slide guards. Future research on preventing falls from roofs should consider the main effects and interactions of the environmental, task-related and personal factors that affect the balance control of workers. Research-supported improvements in the visual and physical characteristics of the roof work environment, the construction materials and methods, and work procedures and practices may result in improved workers' balance control as well as overall safety performance, and would ultimately reduce incidents of falling from a roof.     

Effect of safety boots with toe spring on foot clearance features during walking

Tripping is a primary cause of occupational injury falls, especially among aging workers. This study investigated changes in foot clearance features during the normal walking swing phase affected by adding a toe spring height to safety boots. Gait data were obtained from nine male participants wearing experimental and control shoes via a motion capture system. A principal component analysis was conducted on three-dimensional foot segment trajectories and angles, and plantar surface motions were compared between conditions. Statistical analysis revealed significant principal component score differences between conditions in principal component vectors 1, 3, 5, 6, 8, and 9. The related swing phase three-dimensional plantar surface motion patterns were reconstructed. The results revealed two characteristics of the shoe-plantar surface three-dimensional motion of experimental shoes: higher foot clearance and a relatively straighter forward leg path. It was thus concluded that utilizing safety boots with toe springs may reduce falls in older workers due to occupational trips in industries.     

Effects of age-related gait changes on the biomechanics of slips and falls

A laboratory study was conducted to examine gait changes associated with aging and the effect of these changes on initiation of slips and frequency of falls utilizing newly defined biomechanical parameters of slips and falls. Twenty-eight participants from two age groups (young and old) walked around a circular track at a comfortable pace wearing a safety harness. A slippery floor surface was placed on the walking track over the force plate at random time intervals without the participants' awareness. Synchronized kinetic and kinematic measurements were obtained on both slippery and non-slippery walking surfaces. The results indicated that older participants' horizontal heel contact velocity was significantly faster, step length was significantly shorter, and transitional acceleration of the whole body centre-of-mass (COM) was significantly slower than younger participants. Older participants' initial friction demand, as measured by required coefficient of friction (RCOF), was not significantly different than their younger counterparts. Additionally, older participants slipped longer and faster, and fell more often than younger participants. A comparison of horizontal heel contact velocity for participants who fell with participants who did not fall indicated that, in general, fallers' horizontal heel contact velocity was faster than non-fallers. However, a comparison of RCOF for participants who fell with participants who did not fall suggested that RCOF was not a totally deterministic factor influencing actual fall events. These findings suggest that gait changes associated with aging (especially higher horizontal heel contact velocity and slower transition of the whole body COM) affect initiation of slip-induced falls.     

Pressure thresholds and stiffness on the plantar surface of the human foot

Abstract

A methodology to assess Pressure Discomfort Thresholds (PDT), Pressure Pain Thresholds (PPT) and tissue stiffness on the plantar surface of the foot was developed. Ten male and 10 female participants volunteered for the study. Foot landmarks were used to create a standardised grid-type template of 95 points. For each test point, PPT and PDT values were obtained, and stiffness was calculated for each of the 20 participants. Cluster analyses were performed to determine the regions of similarity for the three dependent variables, PPT, PDT and stiffness. Moran’s-I-index was used to determine the spatial auto correlations. The use of k-means clustering showed five distinct clusters while the three dependent variables showed strong correlations to each other. Morisita’s similarity index was used to check the similarity of the grid among all participants. Both male and female participants showed a Morisita’s index greater than 0.7 confirming the reliability of the foot template.

Practitioner Summary: Pressure Discomfort thresholds (PPT), Pressure pain thresholds (PPT) and tissue stiffness were evaluated at 95 points on the plantar surface of the foot. The PPT and related PDT map are useful to design the footbeds of shoes. Based on the data collected, five distinct clusters of locations were identified.     

针对小儿脑瘫早期诊断的无线传输便携式足底压力分布测量系统的设计

足底压力的大小与分布能反映人体腿、足的结构和功能及整个身体姿势等信息。测试、分析足底应力,对小儿脑瘫的早期诊断具有重要意义。因此研制了一套足底压力分布测量系统并测评其应用价值。本系统由硬件和软件两个部分组成。系统硬件包括12个FlexiForce薄膜测力传感器、信号转换电路、51单片机采集电路;系统软件主要由实时采集模块、数据存储模块、数据计算分析和显示模块等组成。     

Biomechanics of slips.

The biomechanics of slips are an important component in the prevention of fall-related injuries. The purpose of this paper is to review the available literature on the biomechanics of gait relevant to slips. This knowledge can be used to develop slip resistance testing methodologies and to determine critical differences in human behaviour between slips leading to recovery and those resulting in falls. Ground reaction forces at the shoe-floor interface have been extensively studied and are probably the most critical biomechanical factor in slips. The ratio of the shear to normal foot forces generated during gait, known as the required coefficient of friction (RCOF) during normal locomotion on dry surfaces or 'friction used/achievable' during slips, has been one biomechanical variable most closely associated with the measured frictional properties of the shoe/floor interface (usually the coefficient of friction or COF). Other biomechanical factors that also play an important role are the kinematics of the foot at heel contact and human responses to slipping perturbations, often evident in the moments generated at the lower extremity joints and postural adaptations. In addition, it must be realized that the biomechanics are dependent upon the capabilities of the postural control system, the mental set of the individual, and the perception of the environment, particularly, the danger of slipping. The focus of this paper is to review what is known regarding the kinematics and kinetics of walking on surfaces under a variety of environmental conditions. Finally, we discuss future biomechanical research needs to help to improve walkway-friction measurements and safety.     

Effects of aging on the biomechanics of slips and falls

Although much has been learned in recent decades about the deterioration of muscular strength, gait adaptations, and sensory degradation among older adults, little is known about how these intrinsic changes affect biomechanical parameters associated with slip-induced fall accidents. In general, the objective of this laboratory study was to investigate the process of initiation, detection, and recovery of inadvertent slips and falls. We examined the initiation of and recovery from foot slips among three age groups utilizing biomechanical parameters, muscle strength, and sensory measurements. Forty-two young, middle-age, and older participants walked around a walking track at a comfortable pace. Slippery floor surfaces were placed on the track over force platforms at random intervals without the participants' awareness. Results indicated that younger participants slipped as often as the older participants, suggesting that the likelihood of slip initiation is similar across all age groups; however, older individuals' recovery process was much slower and less effective. The ability to successfully recover from a slip (thus preventing a fall) is believed to be affected by lower extremity muscle strength and sensory degradation among older individuals. Results from this research can help pinpoint possible intervention strategies for improving dynamic equilibrium among older adults.     

Kinematics and kinetics of gait on stilts: identification of risk factors associated with construction stilt use

This study investigated kinematics and kinetic strategies and identified risk factors associated with gait on stilts. A six-camera motion-analysis system and two force platforms were used to test 20 construction workers for straight walking or turning, with or without carrying tools while wearing safety shoes or stilts at different heights. The results indicated that gait on stilts is characterised by increases in stride length, step width and the percentage of double support period, decreases in cadence, minimum foot clearance and a weaker heel-strike and push-off. Stilts place greater joint loadings on lower extremities to compensate for the added weight and limitation in joint mobility. Smaller foot clearances found for gait on stilts constitute an increased risk for tripping over obstacles. Workers may need to avoid prolonged use of stilts to alleviate stresses on the joints. This study was conducted to determine to what extent stilts alter the gait strategies and to explain the compensatory movements. Prior to this study, there has been little substantive research to evaluate the stresses and potential injuries associated with stilts.     

Preventing falls from roofs: a critical review

Work-related falls from roofs remain a significant problem for workers in the construction industry. Knowledge about the main causative or initiating factors leading to fall incidents is desperately needed for fall prevention intervention. From biomechanical and psychophysiological perspectives the majority of occupational falls, including falls from roofs, can be regarded as loss-of-balance incidents. The primary objective of this paper is to summarize the current knowledge from multiple fields about factors that are related to the control of balance during roofing work. An extensive literature review identified a number of environmental, task-related and personal factors that degrade the control of balance and could be associated with the initiation of falls from roofs. These factors include visual exposure to elevation; unstable visual cues and inadequate visual information in the work environment; 'confined' and inclined support surfaces; unexpected changes in roof surface properties; load handling; physical exertion; fatigue; task complexity that diverts workers' attention; individual differences; work experience and training; and personal protective equipment. Current measures to reduce falls from roofs focus mainly on fall protection procedures, such as the use of covers, guardrails, safety nets, and personal fall-arrest systems, or the application of warning-line systems, safety monitoring systems, and fall protection plans. In many instances, these procedures are not practical for the industry and current regulations allow the use of alternative means of fall protection, such as slide guards. Future research on preventing falls from roofs should consider the main effects and interactions of the environmental, task-related and personal factors that affect the balance control of workers. Research-supported improvements in the visual and physical characteristics of the roof work environment, the construction materials and methods, and work procedures and practices may result in improved workers' balance control as well as overall safety performance, and would ultimately reduce incidents of falling from a roof.     

Adaptive gait detection based on foot-mounted inertial sensors and multi-sensor fusion

Gait detection plays an important role in areas where spatial-temporal gait parameters are needed. Inertial sensors are now sufficiently small in size and light in weight for collection of human gait data with body sensor networks (BSNs). However, gait detection methods usually rely on careful sensor alignment and a set of rule-based thresholds, which are brittle or difficult to implement. This paper presents an adaptive method for gait detection, which models human gait with a hidden Markov model (HMM), and employs a neural network (NN) to deal with the raw measurements and feed the HMM with classifications. Six gait events are involved for a detailed analysis, i.e., heel strike, foot flat, mid-stance, heel off, toe off, and mid-swing. In order to obtain enough gait data for training a gait model, the gait events are labeled by a rule-based detection method, in which the predefined rules are verified with an optical motion capture system. Experiments were conducted by nine subjects, based on a dual-sensor configuration with one sensor on each foot. Detection performance is quantified using metrics of accuracy, sensitivity and specificity, and the averaged performance values are 98.11%, 94.32% and 98.86% respectively with a timing error less than 2.5 ms.     

Effects of age-related gait changes on the biomechanics of slips and falls

A laboratory study was conducted to examine gait changes associated with aging and the effect of these changes on initiation of slips and frequency of falls utilizing newly defined biomechanical parameters of slips and falls. Twenty-eight participants from two age groups (young and old) walked around a circular track at a comfortable pace wearing a safety harness. A slippery floor surface was placed on the walking track over the force plate at random time intervals without the participants' awareness. Synchronized kinetic and kinematic measurements were obtained on both slippery and non-slippery walking surfaces. The results indicated that older participants' horizontal heel contact velocity was significantly faster, step length was significantly shorter, and transitional acceleration of the whole body centre-of-mass (COM) was significantly slower than younger participants. Older participants' initial friction demand, as measured by required coefficient of friction (RCOF), was not significantly different than their younger counterparts. Additionally, older participants slipped longer and faster, and fell more often than younger participants. A comparison of horizontal heel contact velocity for participants who fell with participants who did not fall indicated that, in general, fallers' horizontal heel contact velocity was faster than non-fallers. However, a comparison of RCOF for participants who fell with participants who did not fall suggested that RCOF was not a totally deterministic factor influencing actual fall events. These findings suggest that gait changes associated with aging (especially higher horizontal heel contact velocity and slower transition of the whole body COM) affect initiation of slip-induced falls.