Dynamic analysis of plastic below-knee drop foot braces

The results of the dynamic analysis of a below-knee drop foot brace made of reinforced polyester are presented. The investigation was carried out on four paralysed patients. It was found that the highest antero-posterior loads occur in stance phase. The antero-posterior loads were, both in stance and in swing phase, greater than the lateral loads. The results indicate that the loads noted in the plastic braces are similar to those found in metal braces.     

Interlimb coordination in cat locomotion investigated with perturbation

Summary During locomotion of decerebrate and awake walking cats, perturbation (mechanical tap) was applied to the paw dorsum of the left forelimb (LF), and the responses of both forelimbs were recorded cinematographically and electromyographically (EMG). When the tap was applied during the LF stance phase, the duration of the ongoing LF stance was shortened by 10%; in the right forelimb (RF), the duration of the concomitant swing was shortened by 32%. A tap during the LF swing phase prolonged the duration of the ongoing LF swing phase and the concomitant RF stance phase by 55 and 15%, respectively. Analysis of RF joint angle excursions showed that the shortening of the RF swing phase was related mainly to acceleration of extension movement in the late swing phase; the prolongation of the RF stance phase was related to prolonged extension movement in the late stance phase. While EMG activities were relevant to these limb movements, a notable observation was that, by tapping the LF during the LF stance phase, EMG activity in the RF extensor started well before onset of the elbow extension movement to place down the limb; without the tap, the extensor activity started shortly after onset of the extension. Closely related to changes in phase durations of each forelimb, the period of bisupport phase where both forelimbs were in stance, was retained for more than 40% of that of unperturbed steps, even when the RF or LF made the first touchdown after the tap. The rostrocaudal level at RF touchdown after the tap was comparable to unperturbed steps. These findings on interlimb relation suggest that neural control ensures coordinated movements between symmetric limbs during locomotion.Supported by grant no. 557033 from the Japanese Ministry of Education, Science, and Culture     

正走和倒走的膝关节生物力学特征比较

目的 比较正走和倒走两种不同行走模式时膝关节的生物力学特征。方法 采用三维运动捕捉系统Vicon T40和测力台AMTI OR6-7采集并比较13名健康青年男性志愿者正走和倒走时的时间、空间、运动学和动力学参数。结果 与正走相比,倒走时的步速、步频和步幅均显著减小,跨步周期和支撑相所占百分比显著增加;在矢状面上,倒走时膝关节活动度、最大屈伸力矩较正走小;在冠状面上,倒走时膝关节内翻外展活动范围也较正走小,内翻力矩峰值在支撑早期较正走小,但在支撑晚期较正走大;地面反作用力在支撑早期较正走大,但在支撑晚期较正走小。结论 倒走和正走膝关节生物力学特征差异明显。与正走相比倒走在支撑相早期能减轻膝关节内侧间室的负荷,而倒走在支撑相晚期对膝关节负荷的影响则尚须进一步研究。     

Three dimensional finite element modelling of metatarsal stresses during running

Abstract

Second metatarsal stress fractures are a problematic injury for runners and are formed when the rate of repair of bone is outpaced by the damage accumulated during loading. Measuring the peak stresses on the bone during running gives an indication of damage accumulation but direct measurement is invasive. Finite element modelling is a viable alternative method of accurately estimating bone stresses but tends to be too computationally expensive for use in applied research. This study presents a novel and simple finite element model which can estimate bone stresses on the second metatarsal during the stance phase of walking and running, accounting for joint reaction forces and soft tissue effects. The influence of the forces and kinematic inputs to the model and the presence of the soft tissues was quantified using a sensitivity analysis. The magnitudes of maximum stress from the model are similar to existing finite element models and bone staple strain gauge values collected during walking and running. The model was found to be most sensitive to the pitch angle of the metatarsal and the joint reaction forces and was less sensitive to the ground reaction forces under the metatarsal head, suggesting that direct measurement of external forces should not be assumed to represent internal stresses.     

Treadmill locomotion in normal mice—Step related multi-channel EMG profiles of thigh muscles

Mouse models are increasingly used in current research on motor disorders. In mice, the myoelectrical activation of thigh muscles during locomotion has not yet, however, been investigated in depth. Especially intramuscular coordination has hardly been clarified. Therefore, the aims of this study were to characterize myoelectrical activity in the vastus lateralis (VL) and the biceps femoris (BF) muscle of the healthy mouse for reference purposes. The VL and the BF muscles of 12 healthy mice performing a total of 1985 steps during treadmill locomotion were investigated with two subcutaneous arrays each incorporating four electrodes. Eight-channel EMG was recorded simultaneously with high-speed videography. The EMG curves of each step were rectified and smoothed by calculating root mean square (RMS) profiles and then time-normalized for comparisons within and between animals. The EMG-activity of both muscles increased during late swing phase. The VL activity rose steeply and peaked during mid-stance phase, while the biceps activity reached a plateau during early stance phase. With increasing gait velocity, stance time decreased. The increase in gait velocity was also associated with greater EMG amplitudes. The results suggest that the BF lifts the lower hind leg during swing phase and stabilizes the leg during stance, while the VL bears the weight of the body during the stance phase.     

Excitability of the soleus H-reflex arc during walking and stepping in man

Summary In eight normal subjects, the excitability of the soleus (Sol) H-reflex was tested in parallel with Sol length changes, EMGs of leg and thigh muscles and ground contact phases, during three different pacing movements: bipedal treadmill walking, single limb treadmill walking, and single-limb stepping on one spot. A computerized procedure was used which compensated for changes in stimulus effectiveness that occurred during free motion. In the three paradigms examined, significant excitability modulations were observed with respect to a control level determined in standing weight-bearing position. During bipedal treadmill walking, excitability was decreased in the early stance, maximally enhanced in the second half of the stance, and again decreased during the end-stance and the whole swing phase, with a minimum value around the toe off period. The main modulation pattern was retained during single-limb treadmill walking. During single-limb stepping on one spot, the stance-phase increase in excitability and the swing phase depression were still present. However, in the second half of the swing phase, reflex responsiveness returned to reference level, which was maintained during the subsequent contact period. Moreover, a decrease in reflex excitability was detected around the mid-stance. The time course of the described modulations was only partly correlated with the EMG and length changes of the Sol muscle. Furthermore, in the three movements tested, during the early stance phase, the excitability of the H-reflex arc did not correspond to the one expected on the basis of the available H-reflex studies performed under static conditions. It is suggested that, at least in certain stride phases (e.g. around the early contact period), an active regulation affects the transmission in the Sol myotatic arc during the pacing movements investigated.     

Vibration-induced changes in EMG during human locomotion

The present study was set up to examine the contribution of Ia afferent input in the generation of electromyographic (EMG) activity. Subjects walked blindfolded along a walkway while tendon vibration was applied continuously to a leg muscle. The effects of vibration were measured on mean EMG activity in stance and swing phase. The results show that vibration of the quadriceps femoris (Q) at the knee and of biceps femoris (BF) at the knee enhanced the EMG activity of these muscles and this occurred mainly in the stance phase of walking. These results suggest involvement of Ia afferent input of Q and BF in EMG activation during stance. In contrast, vibration of muscles at the ankle and hip had no significant effect on burst amplitude. Additionally, the onset time of tibialis anterior was measured to look at timing of phase transitions. Only vibration of quadriceps femoris resulted in an earlier onset of tibialis anterior within the gait cycle, suggesting involvement of these Ia afferents in the triggering of phase transitions. In conclusion, the results of the present study suggest involvement of Ia afferent input in the control of muscle activity during locomotion in humans. A limited role in timing of phase transitions is proposed as well.     

基于统计参数映射分析跑鞋跟掌落差对下肢关节负荷的影响

目的 探讨在相同跑速下穿着不同落差跑鞋对下肢关节负荷的影响,为跑鞋设计和跑步者选购跑鞋提供依据。方法 18名男性跑步者分别穿着零落差和10 mm落差跑鞋以(4.0±0.2) m/s速度完成测试,使用红外高速运动捕捉系统和三维测力台同步采集下肢运动学参数和地面反作用力(ground reaction force, GRF)。使用统计参数映射法(statistical parameter mapping, SPM)分析跑鞋跟掌落差对支撑期垂直GRF、下肢关节三维力矩的影响。结果 跑鞋跟掌落差对垂直GRF无影响,对下肢关节部分力矩-时间序列影响显著。与穿着零落差跑鞋相比,穿着10 mm落差跑鞋在27%～38%支撑期髋关节内旋力矩增加,在47%～75%支撑期膝关节伸展力矩增加,在16%～33%、25%～30%、12%～25%支撑期踝关节跖屈力矩、外翻力矩和外旋力矩降低。结论 与穿着零落差跑鞋相比,穿着10 mm落差跑鞋在支撑前期髋关节负荷增加,踝关节负荷降低,在支撑中期膝关节负荷增加。建议跑步者结合自身特点及跑鞋跟掌落差对下肢关节负荷特征的影响,选择适合自己的跑鞋。     

A finite element model to assess transtibial prosthetic sockets with elastomeric liners

People with transtibial amputation often experience skin breakdown due to the pressures and shear stresses that occur at the limb-socket interface. The purpose of this research was to create a transtibial finite element model (FEM) of a contemporary prosthesis that included complete socket geometry, two frictional interactions (limb-liner and liner-socket), and an elastomeric liner. Magnetic resonance imaging scans from three people with characteristic transtibial limb shapes (i.e., short-conical, long-conical, and cylindrical) were acquired and used to develop the models. Each model was evaluated with two loading profiles to identify locations of focused stresses during stance phase. The models identified five locations on the participants’ residual limbs where peak stresses matched locations of mechanically induced skin issues they experienced in the 9 months prior to being scanned. The peak contact pressure across all simulations was 98 kPa and the maximum resultant shear stress was 50 kPa, showing reasonable agreement with interface stress measurements reported in the literature. Future research could take advantage of the developed FEM to assess the influence of changes in limb volume or liner material properties on interface stress distributions.

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Graphical abstract Residual limb finite element model. Left: model components. Right: interface pressures during stance phase

     

Hamstrings and quadriceps muscle contributions to energy generation and dissipation at the knee joint during stance,swing and flight phases of level running

BackgroundHuman movements involve the generation and dissipation of mechanical energy at the lower extremity joints. However, it is unclear how the individual knee muscles contribute to the energetics during running.ObjectiveThis study aimed to determine how each hamstring and quadricep muscle generates and dissipates energy during stance, swing and flight phases of running.MethodsA three-dimensional lower extremity musculoskeletal model was used to estimate the energetics of the individual hamstrings (semimembranosus, semitendinosus, biceps femoris long and short-heads) and quadriceps (rectus femoris, vastus medialis, vastus intermedius and vastus lateralis) muscles for a male subject during level running on a treadmill at a speed of 3.96 m/s.ResultsOur findings demonstrated that the knee flexors generated energy during stance phase and dissipated energy during swing phase, while the knee extensors dissipated energy during the flexion mode of both stance and swing phases, and generated energy during the extension mode. During flight phase, the knee flexors generated energy during the flight phase transiting from toe-off to swing, while the knee extensors generated energy during the flight phase transiting from swing to heel-strike.ConclusionIndividual knee flexors and extensors in the hamstrings and quadriceps play important roles in knee joint energetics, which are necessary for proper execution and stabilization of the stance, swing and flight phases of running.     

Post-effect of forward and backward locomotion on body orientation in space during quiet stance

Neural circuits responsible for stance control serve other motor tasks as well. We investigated the effect of prior locomotor tasks on stance, hypothesizing that postural post-effects of walking are dependent on walking direction. Subjects walked forward (WF) and backward (WB) on a treadmill. Prior to and after walking they maintained quiet stance. Ground reaction forces and centre of foot pressure (CoP), ankle and hip angles, and trunk inclination were measured during locomotion and stance. In WF compared to WB, joint angle changes were reversed, trunk was more flexed, and movement of CoP along the foot sole during the support phase of walking was opposite. During subsequent standing tasks, WB induced ankle extension, hip flexion, trunk backward leaning; WF induced ankle flexion and hip extension. The body CoP was displaced backward post-WB and forward post-WF. The post-effects are walking-direction dependent, and possibly related to foot-sole stimulation pattern and trunk inclination during walking.     

伴有足中关节炎的扁平足患者矫正鞋垫的生物力学研究

针对伴有足中关节炎的扁平足患者, 研究不同结构和材料刚度的矫正鞋垫对其足部应力集中和内部关节软骨及筋膜应力的作用效果。在有限元分析的基础上, 结合正交实验设计, 利用CT图像数据建立患者足部及矫正鞋垫有限元模型。随后, 通过footscan系统对支撑相期间足底各区域应力和接触面积进行测量, 验证仿真结果的准确性。然后, 根据有限元分析结果, 对比分析矫正鞋垫的作用效果。结果表明, 足弓高度为30 mm, 楔形角度为5°, 刚度为1 MPa的矫正鞋垫的作用效果最优。与裸足时的应力峰值相比, 足跟区表面和内部的应力峰值分别降低了62.5% (由0.152 MPa降至0.057 MPa)和77.9% (由0.245 MPa降至0.054 MPa);足跖区表面和内部的应力峰值分别降低了56.0% (由0.125 MPa降至0.055 MPa)和72.9% (由0.192 MPa降至0.052 MPa)。相比普通接触式鞋垫, 足底应力分布更均匀, 舟楔关节软骨及筋膜应力(拉伸方向)更小。研究结果为这种复合病症下具有复合作用的矫正鞋垫设计提供数据基础, 对扁平足与足中关节炎的联合治疗具有临床意义。     

即刻改变触地方式对着鞋跑时内侧纵弓在体运动学的影响

目的 探究即刻转换触地方式对着鞋跑步时内侧纵弓在体运动学的影响。 方法 采用高速双平面荧光透视成像系统采集 15 名健康男性跑者即刻改变触地方式前后右足在跑步支撑阶段[跑速:(3±0. 15) m/ s]的荧光图像。根据 CT 图像重建第 1 跖骨和跟骨三维骨骼模型及其局部坐标系,并通过 3D-2D 配准获取内侧纵弓在跑步支撑期的 6 自由度(six degree of freedom,6 DOF) 数据(简化为第 1 跖骨相对跟骨的运动)。 采用一维统计参数映射(statistical parametric mapping,SPM)比较即刻改变触地方式前后内侧纵弓的 6 DOF 运动趋势,并对其特征值进行配对样本 t 检验。 结果 相比后跟跑,即刻前掌跑时,在支撑期的 15% ~ 21% 第 1 跖骨相对跟骨的外移、支撑期 17% ~45% 第 1 跖骨的前移和支撑期的 18% ~ 39% 第 1 跖骨的背屈均显著增加(P<0. 05)。 即刻前掌跑时,第 1 跖骨相对跟骨的前移最大值、背屈最大值、前后平移活动范围及内侧纵弓压缩变化量均显著增加(P<0. 05)。 结论 由习惯后跟跑即刻转换为前掌跑后,内侧纵弓矢状面的形变显著增加,尤其是内侧纵弓的压缩变化量增加约 10% ,可能有助于其弹性能量的储存与释放。     

Stimulation of the group I extensor afferents prolongs the stance phase in walking cats

Group I afferents in nerves innervating the lateral gastrocnemius-soleus (LG-Sol), plantaris (P1), and vastus lateralis/intermedius (VL/VI) muscles were stimulated during walking in decerebrate cats. The stimulus trains were triggered at a fixed delay following the onset of bursts in the medial gastrocnemius muscle. Stimulation of all three nerves with long stimulus trains (>600 ms) prolonged the extensor bursts and delayed the onset of flexor burst activity. LG-Sol nerve stimulation had the strongest effect; often delaying the onset of flexor burst activity until the stimulus train was ended. By contrast, flexor bursts were usually initiated before the end of the stimulus train to the P1 and VL/VI nerves. The minimum stimulus strength required to increase the cycle period was between 1.3×threshold and 1.6×threshold for all three nerves. Simultaneous stimulation of the P1 and VL/VI nerves produced a larger effect on the cycle period than stimulation of either nerve alone. The spatial summation of inputs from knee and ankle muscles suggests that the excitatory action of the group I afferents during the stance phase is distributed to all leg extensor muscles. Stimulation of the group I afferents in extensor nerves generally produced an increase in the amplitude of the heteronymous extensor EMG towards the end of the stance phase. This increase in amplitude occurred even though there were only weak monosynaptic connections between the stimulated afferents and the motoneurones that innervated these heteronymous muscles. This suggests that the excitation was produced via oligosynaptic projections onto the extensor motoneuronal pool. Stimulation with 300 ms trains during the early part of flexion resulted in abrupt termination of the swing phase and reinitiation of the stance phase of the step cycle. The swing phase resumed coincidently with the stimulus offset. Usually, stimulation of two extensor nerves at group I strengths was required to elicit this effect. We were unable to establish the relative contributions of input from the group 1a and group 1b afferents to prolonging the stance phase. However, we consider it likely that group Ib afferents contribute significantly, since their activation has been shown to prolong extensor burst activity in reduced spinal preparations. Thus, our results add support to the hypothesis that unloading of the hindlimb during late stance is a necessary condition for the initiation of the swing phase in walking animals.     

The rat lumbosacral spinal cord adapts to robotic loading applied during stance

Load-related afferent information modifies the magnitude and timing of hindlimb muscle activity during stepping in decerebrate animals and spinal cord-injured humans and animals, suggesting that the spinal cord mediates load-related locomotor responses. In this study, we found that stepping on a treadmill by adult rats that received complete, midthoracic spinal cord transections as neonates could be altered by loading the hindlimbs using a pair of small robotic arms. The robotic arms applied a downward force to the lower shanks of the hindlimbs during the stance phase and measured the position of the lower shank during stepping. No external force was applied during the swing phase of the step. When applied bilaterally, this stance force field perturbed the hindlimb trajectories so that the ankle position was shifted downward during stance. In response to this perturbation, both the stance and step cycle durations decreased. During swing, the hindlimb initially accelerated toward the normal, unperturbed swing trajectory and then tracked the normal trajectory. Bilateral loading increased the magnitude of the medial gastrocnemius electromyographic (EMG) burst during stance and increased the amplitude of the semitendinosus and rectus femoris EMG bursts. When the force field was applied unilaterally, stance duration decreased in the loaded hindlimb, while swing duration was decreased in the contralateral hindlimb, thereby preserving interlimb coordination. These results demonstrate the feasibility of using robotic devices to mechanically modulate afferent input to the injured spinal cord during weight-supported locomotion. In addition, these results indicate that the lumbosacral spinal cord responds to load-related input applied to the lower shank during stance by modifying step timing and muscle activation patterns, while preserving normal swing kinematics and interlimb coordination.     

Positive force feedback in human walking

The objective of this study was to determine if load receptors contribute to the afferent-mediated enhancement of ankle extensor muscle activity during the late stance phase of the step cycle. Plantar flexion perturbations were presented in late stance while able-bodied human subjects walked on a treadmill that was declined by 4%, inclined by 4% or held level. The plantar flexion perturbation produced a transient, but marked, presumably spinally mediated decrease in soleus EMG that varied directly with the treadmill inclination. Similarly, the magnitude of the control step soleus EMG and Achilles' tendon force also varied directly with the treadmill inclination. In contrast, the ankle angular displacement and velocity were inversely related to the treadmill inclination. These results suggest that Golgi tendon organ feedback, via the group Ib pathway, is reduced when the muscle–tendon complex is unloaded by a rapid plantar flexion perturbation in late stance phase. The changes in the unload response with treadmill inclination suggest that the late stance phase soleus activity may be enhanced by force feedback.     

Stresses in the normal pelvis

This paper deals in the stresses in the hip bone as a result of the forces in the muscles and ligaments acting on it. The finite element method is employed and stresses during standing on one leg stance are presented. Goodman's type joint element is used to represent the thin layer of compact bone. The analysis predicts that the maximum stresses (of the order of 0.57M_B MPa) occur in the acetabulum region and the ilium is a region of comparatively low stresses. Possibly it is the first attempt to determine stresses theoretically.     

Three-dimensional kinematics and dynamics of the foot during walking: a model of central control mechanisms

The foot is a critical interface between the body and supporting surface during walking, but there is no coherent framework on which to model the dynamics of the stance and swing phases. To establish this framework, we studied the rotational and translational dynamics of foot movement in three dimensions with a motion detection system (OPTOTRAK), while subjects walked on a treadmill. Positions, velocities, and durations were normalized to leg-length and gravity. Foot position and rotation at toe-off were closely related to walking velocity. Foot pitch at toe clearance increased with walking velocity, but the medial–lateral and vertical toe positions were unaltered. Phase–plane trajectories along the fore-aft direction, i.e., plots of toe velocity versus position, were circular during the swing phases, with radii proportional to walking velocity. Peak forward, lateral, and upward velocities were linearly related to corresponding excursions, forming main sequences. A second order model predicted the changes in toe position and velocity, and the approximately hyperbolic decrements in duration as a function of walking velocity. The model indicates that the foot is controlled in an overdamped manner during the stance phase and as a feedback-controlled undamped pendulum during the swing. The data and model suggest that the state of the foot at toe-off, set by walking velocity during the stance phase, determines the dynamics of the swing phase. Thus, in addition to determining locomotion kinematics, walking velocity plays a critical role in determining the phase–plane trajectories and main sequence relationships of foot movements during the swing phases.     

足踝步态模拟机动力学特性仿真及实验验证

目的 研究足踝步态模拟机动力学特性,仿真着地相中的足底垂直、前后、水平3个足底反力,并在实验台中验证。方法 运用设计的5自由度步态模拟机,建立Adams虚拟样机和足踝模型（包含足部主要韧带和跖腱膜、足底软组织及跟腱力）,对其进行动力学仿真,并把仿真中的控制规律运用到实验台验证;将仿真和实验中测力板测得的足底反力与仿真和真实数据比较。结果 着地相进程中3个方向的足底反力与实际步态中吻合度较高,足部的韧带和跖腱膜、跟腱和软组织等对正确的步态有重要的影响,步态实验台能够很好重复仿真特性。结论 模拟机具备仿真人体步态着地相的能力,为活体无法进行测量的实验提供临床研究平台。     

Electromyography and cinematography of leg and foot (“normal” and flat) during walking

Electromyography with fine-wire electrodes and special equipment for synchronized motion pictures were used to study six muscles of the leg and foot during walking in five different ways in ten “normal” and ten flatfooted subjects. Detailed analyses and comparisons of the two groups are described and discussed. Tibialis Anterior has two peaks of activity at heel-strike and toe-off of the stance phase; is inactive during mid-swing and middle of the stance phase; is active at full-foot in flatfooted subjects, and generally more active during toe-out and toe-in walking. Tibialis posterior is inactive through the swing phase. In flatfooted persons it becomes activated at heel-strike and more active at full-foot during level walking. The toe-out position reduces its activity. Flexor hallucis longus is most active in mid-stance; during toe-out walking, activity increases in both phases, generally being more active in “normal” persons. Peroneus longus is most active at mid-stance and heel-off and generally more active in flatfooted persons. Abductor hallucis and Flexor digitorum brevis are generally more active in flatfooted persons. An important regular pattern of inversion and eversion during the walking cycle is described. Contingent arch support by muscles rather than continuous support is the rule, muscles being recruited to compensate for lax ligaments and special stresses during the walking cycle.