Reaction Force Distribution Research Articles

The method for calculating the traction resistance of a flat disk

Scuffler with flat discs are widely used in areas, which are subject to wind erosion of soils, to cover moisture on the stubble fields. Flat discs do not wrap the layers they remove, but only loosen them, shifting them aside. It is preferable to use such scrapers during presowing tillage and on steam, since in this case there is less sputtering of the soil, and its lower (moist) layers are not carried to the surface. Therefore, many industrially manufactured scufflers are equipped with flat discs, and the task of constructing a mathematical model for the interaction of such discs with soil is topical. Many mathematical models of the disc-soil interaction, taking into account the distribution of soil reaction forces on the disk, have been proposed, but all these models were constructed assuming that the disk is moving in its plane. Therefore, they are not applicable to the disk of a lakeshield moving with a non-zero angle of attack in the soil. The purpose of this work is to construct a mathematical model that allows calculating the traction resistance of a disk moving with a given angle of attack. The basic assumptions made in the construction of this model: the speed of the translational movement of the disk and its depth are constant; friction in the disk bearing can be neglected; the soil pressure on the lateral surface of the disc and the force of the soil reactions per unit length of its blade can be replaced by their mean values. An explicit expression is obtained for the traction resistance of a disk of a scuffler moving with an angle of attack, depending on its relative depth, the angle of attack, and the empirical coefficients. The adequacy of the constructed mathematical model is confirmed by comparison with known experimental data. It makes it possible to significantly reduce the number of full-scale experiments on the study of the interaction of flat discs of a scuffler with the soil, replacing them with computational ones, and reasonably carry out power and strength calculations of such discs. In addition, it can be used to optimize the parameters of the flat discs of the scuffler.

Combining Push-Off Power and Nonlinear Damping Behaviors for a Lightweight Motor-Driven Transtibial Prosthesis

Transtibial prostheses play an important role in below-knee amputees’ daily activities. Our previous study presented a lightweight prosthesis with damping behaviors, which can adapt to different terrains. However, the proposed prosthesis cannot provide push-off during the stance phase. In this paper, we redesigned the mechanical structure, combining push-off and damping behaviors. The Peking University Robotic Trantibial Prosthesis (PKU-RoboTPro-) II makes a trade-off between push-off power and lightweight. Three unilateral transtibial subjects participated in the study. Gait symmetry and metabolic cost of walking with the proposed prosthesis were evaluated under conditions of three terrains and four walking speeds. The gait symmetry of the subjects using the prosthesis combining push-off and damping behaviors in stance time and ground reaction force distribution are improved. Meanwhile, the PKU-RoboTPro-II with a push-off mode can reduce energy expenditure, with an average 14% $\pm$ 8% reduction and a maximal 31% reduction under different conditions, compared with a non-push-off mode. When the weight of the lithium-ion rechargeable battery is 0.28 kg (2.6 Ah), it enables the new prosthesis combining push-off and damping behaviors to walk approximately 10 000 strides, on average.

Three-Axis Ground Reaction Force Distribution during Straight Walking

We measured the three-axis ground reaction force (GRF) distribution during straight walking. Small three-axis force sensors composed of rubber and sensor chips were fabricated and calibrated. After sensor calibration, 16 force sensors were attached to the left shoe. The three-axis force distribution during straight walking was measured, and the local features of the three-axis force under the sole of the shoe were analyzed. The heel area played a role in receiving the braking force, the base area of the fourth and fifth toes applied little vertical or shear force, the base area of the second and third toes generated a portion of the propulsive force and received a large vertical force, and the base area of the big toe helped move the body’s center of mass to the other foot. The results demonstrate that measuring the three-axis GRF distribution is useful for a detailed analysis of bipedal locomotion.

A fusion framework to estimate plantar ground force distributions and ankle dynamics

Gait analysis plays an important role in several conditions, including the rehabilitation of patients with orthopaedic problems and the monitoring of neurological conditions, mental health problems and the well-being of elderly subjects. It also constitutes an index of good posture and thus it can be used to prevent injuries in athletes and monitor mental health in typical subjects. Usually, accurate gait analysis is based on the measurement of ankle dynamics and ground reaction forces. Therefore, it requires expensive multi-camera systems and pressure sensors, which cannot be easily employed in a free-living environment. We propose a fusion framework that uses an ear worn activity recognition (e-AR) sensor and a single video camera to estimate foot angle during key gait events. To this end we use canonical correlation analysis with a fused-lasso penalty in a two-steps approach that firstly learns a model of the timing distribution of ground reaction forces based on e-AR signal only and subsequently models the eversion/inversion as well as the dorsiflexion of the ankle based on the combined features of e-AR sensor and the video. The results show that incorporating invariant features of angular ankle information from the video recordings improves the estimation of the foot progression angle, substantially.

Rigidity and moment distribution of steel-concrete composite waffle floor systems considering the spatial effect

A steel-concrete composite waffle floor system (SCCWFS) that consists of orthogonal steel beams and a flat RC slab has potential applications in long-span building floors because of its large loading capacity, low depth-to-span ratio, and excellent ductility, as demonstrated by a previous experimental program. According to the test results, the spatial composite effect between the orthogonal steel beams and concrete slab significantly influences the performance of the SCCWFS. However, the complexity of the spatial composite effect in the SCCWFS makes it much more difficult to determine the rigidity and the internal force distribution in a routine design practice than the one-way steel-concrete composite floor or the RC waffle slab. To address this problem, a parameterized grillage method is developed in which intrinsic factors are defined to describe the critical properties of the deformation pattern, the reaction force and moment distribution of the SCCWFS; relation factors are defined to relate these properties of the SCCWFS to that of its corresponding steel grillage. Based on the parameterized grillage method, parametric analyses are conducted using a beam-shell mixed finite-element (FE) model and the influence of various parameters on intrinsic and relation factors is investigated, in which the beam height, slab thickness, length-to-width ratio, and so on are shown to be of importance. The data of a total of 5190 numerical models associated with seven parameters covering almost all the practical cases are then obtained, and a step-shaving procedure is proposed to derive formulas that are influenced by multiple variables. Based on the parameterized grillage method and the step-shaving procedure, formulas to predict the vertical displacements, reaction force and moment distribution of the SCCWFS are derived and verified. Finally, design procedures, recommendations and simplified forms of the formulas are proposed, in which the formulas are proved to have an error of approximately 10%.

Buckling behaviors and simplified design method for steel silos under locally distributed axial load

Buckling behaviors of steel silos subjected to locally distributed axial load (LDAL) were studied by a Finite Element Model (FEM), which was verified by available test and analytical results. Studied parameters included the internal pressure, the Local edge load Center Angle (LCA) and the radius-to-thickness ratio (R/t) of a silo. Buckling modes, distributions of reaction forces along the silo bottom edge and buckling stresses were presented. FEM simulations showed that a compression arch was formed on the silo wall to transfer the LDAL to boundaries; and between the feet of compression arch the reaction was in tension. The span and the height of the compression arch almost did not change with the varying of LCA for silos having the same internal pressure and R/t. However, the height of the compression arch decreased with the increase in internal pressure. A silo under LDAL was more likely failed by elastic buckling when the internal pressure was at low level; and at this circumstance the buckling stress increased with the increase in internal pressure. At high level of internal pressure, buckling failure modes of a silo under LDAL changed from elastic buckling to elastic-plastic buckling; and the buckling stress decreased with the increase in internal pressure. For silos with same internal pressure and R/t, the buckling stress decreased with the increase in LCA. Design equations in EC3-4-1 could overestimate the buckling stress of steel silos under combination of internal pressure and LDAL. Based on parameter study results, a practical design equation was proposed for calculating the buckling stress of a steel silo under combined internal pressure and LDAL. Buckling stresses predicted by the proposed equation agreed well with those obtained by FEM.

Metallic Fixation of Mandibular Segmental Defects: Graft Immobilization and Orofacial Functional Maintenance.

Background:The aim of this study is to investigate the behavior of the healthy mandible under maximum molar bite force to demonstrate the problems associated with the current standard of care procedures for mandibular segmental defect reconstruction (ie, use of Ti–6Al–4V hardware and either a single- or double-barrel fibular graft). With current Ti–6Al–4V mandibular reconstruction hardware, there is a significant stiffness mismatch among the hardware, graft, and the remaining host anatomy. How the distribution of mechanical forces through the mandible is altered after a segmental bone loss and reconstruction is incompletely understood.Methods:We studied a healthy adult mandible for stress, strain, and reaction force distribution during normal mastication. Stress distribution of this model was then used to study problems encountered after mandibular segmental defect reconstructive surgery. We model the use of both single- and double-barrel fibular grafts to repair the loss of the left M1–3 containing segment of the mandible. These simulations were done using 2 sets of plates with different thicknesses.Results:We found that the stiffness mismatching between the fixation hardware and the graft and host bone causes stress shielding of that bone and stress concentrations in the fixation hardware and screws. These effects are expected, especially during the bone healing period. However, long term, this abnormal stress–strain distribution may lead to either the hardware’s failure due to stress concentration or graft failure due to bone resorption as a result of stress shielding. We found that the stress–strain distribution is more normal with a double-barrel fibular graft. Additionally, we found that thinner fixation plates can reduce stress shielding.Conclusion:The proposed model can be used to evaluate the performance and optimization of the fixation device.

Characteristics of autocorrelation structure of lower extremity functional laterality in disturbed and undisturbed bipedal upright stance

PurposeIt is posited that functional laterality is influenced by the generation and conduction of neural signals and therefore associated with sensorimotor control. The question arises if symmetry or asymmetry in sensorimotor processing affects the development of symmetric or asymmetric motor programs in the lower extremities. The purpose of the study was to examine the mechanisms of the human mobility moto-control – the process of maintaining body balance in a standing position through an appropriate course of distribution of ground reaction forces in a time frame, in a situation requiring lower extremity Movement symmetry.MethodsThe autocorrelation function was calculated for ground reaction forces (in the three orthogonal axes) registered during 45 s of bipedal upright stance in two conditions (eyes open and closed).ResultsMinor albeit significant deficiencies in postural muscle control were revealed as a function of time, as evidenced in the decay of the autocorrelation function to zero (T<sub>0</sub>) between the right and left foot for the mediolateral ground reaction force signal. However, the results attest to symmetrical sensorimotor control between both feet.ConclusionsMotor actions (postural corrections) performed in long-duration tasks may have less of an effect on sensorimotor control than those applied in shorter duration projections. ANOVA and correlation analysis (across all variables) of the right and left foot T0 indicate considerable symmetry in the control of force magnitude and direction during upright standing.

Development of modelling strategies for two-way RC slabs

Analyses of tested two-way reinforced concrete (RC) slabs were carried out with varying modelling choices to develop better modelling strategies. The aim was to study how accurately the response of a slab subjected to bending could be predicted with nonlinear finite element (FE) analysis using three-dimensional (3D) continuum elements, and how the modelling choices might influence the analysis results. The load-carrying capacity, load–deflection response, crack pattern and reaction-force distribution of the two-way slab studied were compared to experimental data available. The influence of several modelling parameters was investigated, including geometric nonlinearity, element properties, concrete model, reinforcement model and boundary condition. The results show the possibility of accurately reflecting the experimental results concerning load-carrying capacity, load–deflection response and crack pattern giving proper modelling choices. Moreover, the reaction force distribution was found to be highly influenced by the stiffness of the supports.

Parameter Study of a New Strut-and-Tie Model for a Thick Cap with Six Piles

A comprehensive strut-and-tie model is a function of the nodes, struts, ties, model types, and pile reaction force. Because each element has more than one solution, the function is a problem of permutations and combinations. This paper presents a new strut-and-tie model that yields a satisfactory simulation result. In the model, a model type of truss action, direct arch action, or a combination of both actions was selected independently for the side and angle piles. The node and tie parameters were also modified. The pile reaction force distribution and the failure mechanism for inclined struts were also considered. However, because the authors’ previous study did not include a detailed analysis or an in-depth exploration, the effect of these critical factors is discussed in this paper at length. The model, which was programmed using the MATLAB language, was used to sequentially analyze the possible solutions for each member (nodes, ties, and struts). Different solutions for the ratio of truss action and direct arch action were also compared. The inclined struts with variable cross sections were tested under various failure mechanisms. Furthermore, the effect of the pile reaction force, which was distributed using model test measurements and theoretical (elastic or rigid) analyses, was analyzed. Comparison of the solutions indicated that the function f, which included the essential elements described above, was both rational and accurate.

The generation of centripetal force when walking in a circle: insight from the distribution of ground reaction forces recorded by plantar insoles.

BackgroundTurning involves complex reorientation of the body and is accompanied by asymmetric motion of the lower limbs. We investigated the distribution of the forces under the two feet, and its relation to the trajectory features and body medio-lateral displacement during curved walking.MethodsTwenty-six healthy young participants walked under three different randomized conditions: in a straight line (LIN), in a circular clockwise path and in a circular counter-clockwise path. Both feet were instrumented with Pedar-X insoles. An accelerometer was fixed to the trunk to measure the medio-lateral inclination of the body. We analyzed walking speed, stance duration as a percent of gait cycle (%GC), the vertical component of the ground reaction force (vGRF) of both feet during the entire stance, and trunk inclination.ResultsGait speed was faster during LIN than curved walking, but not affected by the direction of the curved trajectory. Trunk inclination was negligible during LIN, while the trunk was inclined toward the center of the path during curved trajectories. Stance duration of LIN foot and foot inside the curved trajectory (Foot-In) was longer than for foot outside the trajectory (Foot-Out). vGRF at heel strike was larger in LIN than in curved walking. At mid-stance, vGRF for both Foot-In and Foot-Out was higher than for LIN foot. At toe off, vGRF for both Foot-In and Foot-Out was lower than for LIN foot; in addition, Foot-In had lower vGRF than Foot-Out. During curved walking, a greater loading of the lateral heel occurred for Foot-Out than Foot-In and LIN foot. On the contrary, a smaller lateral loading of the heel was found for Foot-In than LIN foot. At the metatarsal heads, an opposite behaviour was seen, since lateral loading decreased for Foot-Out and increased for Foot-In.ConclusionsThe lower gait speed during curved walking is shaped by the control of trunk inclination and the production of asymmetric loading of heel and metatarsal heads, hence by the different contribution of the feet in producing the body inclination towards the centre of the trajectory.

A-19 入浴姿勢における浴槽壁面反力の推定アルゴリズムの構築(映像分析,推定,構造)

In order to improve comfort in bathing, the relationship between the biomechanical load and the bathtub shape has to be clarified. For this purpose, many bathing experiments had to be conducted since it was necessary to measure the reaction forces acting on a human from the bathtub experimentally. The objective of this study was to construct an algorithm to estimate reaction forces from bathtun in order to calculate joint torque as biomechanical loads without bathing experiments. This algorithm calculates distribution of reaction forces which minimizes weighted summation of i) sum of squares of reaction forces, ii) joint torques of hip and knee joints and iii) friction force of the back, considering gravity, buoyancy and passive elastic joint torque. Weighting were expressed as a function of bathing posture including parameters determined for each person to reflect influence of differences among the individual. In order to examine this algorithm, a bathing experiment to obtain the data of bathing posture and reaction forces for 10 subjects and 24 posture conditions was conducted. It was found that the estimated reaction forces were consistent well with the measured values.

Short- and long-term outcomes after arthroscopic treatment of young large breed dogs with medial compartment disease of the elbow.

To report short- and long-term outcomes after arthroscopic treatment in young large breed dogs affected by medial coronoid process disease (MCPD) and identify variables affecting outcome. Prospective observational case series. Large breed dogs <3 years old (n = 15; 23 elbows). MCPD was confirmed by radiography, computed tomography, and arthroscopy. Dogs were treated by arthroscopy. Variables recorded at time of treatment included radioulnar incongruity (RUI) and degree of cartilage erosion. Variables recorded before, 6 weeks, and ≥23 months after surgery included radiographic score for osteoarthritis, trochlear notch sclerosis, muscle circumference, range of motion (ROM), and the load distribution of vertical ground reaction forces between thoracic and pelvic limbs. A greater load distribution to the pelvic limbs was identified preoperatively in dogs with RUI than in dogs with congruent elbows. Load distribution was not significantly improved at 6 weeks compared with preoperatively. Muscle circumference and vertical impulse distributions were improved at long-term evaluation despite an increased osteoarthritis score. This improvement was more obvious in dogs with RUI or a high degree of cartilage erosion at initial presentation. Some evidence of improvement in long-term function was found in dogs with MCPD after arthroscopic treatment. RUI and cartilage erosion at the time of diagnosis were associated with more lameness preoperatively but did not affect the final gait assessment or osteoarthritis score in this small cohort.

Система управління режимом дотримання рівноваги антропоморфним крокуючим апаратом

The paper provides a solution to the problem of the control system compliance regime equilibrium anthropomorphic walking machine on any solid surface by applying the principle of tracking the movement of the point of the center of mass system and the reaction force supporting surface. Used the concept of a distributed control system with the optimal criterion of balancing and adjusting the current position AKA by solving the inverse kinematics problem using adaptive neuro-fuzzy network forecasting. Moving units walking machine is performed using PI2D regulator and determine its current position anthropomorphic walking machine is performed by monitoring the distribution of reaction forces on the supporting surface . For the construction and validation of the control system modeling method used : Hardware in the loop.

Evaluation of Mitral Valve Dynamics

Mitral valve (mv) repair is the preferred treatment for patients with mv insufficiency. The unsolved problem in MV repair surgery is predicting the optimal repair for each patient. This is in part due to lack of physiological imaging modalities to provide this information prior to or at the time of valve repair. Moreover, the majority of cases have complex pathophysiological involvement including annular enlargement, chordal lengthening, chordal rupture, calcification, and ultimately lack of proper leaflet coaptation. Current clinical 3-dimensional (3D) transesophageal echocardiography (TEE) can demonstrate volumetric morphology of the MV apparatus. However, biomechanical information is not available from 3D echocardiography. If imaging techniques can be combined with appropriate computational MV evaluation methods, then improved diagnosis and therapeutic approaches to MV repair can be developed. In the present study, we describe a novel comprehensive evaluation protocol to improve diagnosis and treatment of MV pathology by combining 3D TEE and computational simulation techniques (Fig. 1). Virtual MV models were created by utilizing 3D TEE data of patients with normal and pathological MVs followed by computational simulations of MV function. Computational simulations clearly demonstrated deformation and stress distribution of the MV structure across the cardiac cycle at a microsecond scale and corresponded well to 3D TEE data (Figs. 2 and ​and3,3, Online Videos 1, 2, 3, and 4). Here we present 4 case studies (1 normal and 3 different types of pathological MVs). Figure 1 Flow Chart for Virtual MV Modeling and Computational Simulation of MV Function Figure 2 Images of a Normal MV Figure 3 Images of a Pathological MV With Posterior Chordal Rupture Case 1 (Fig. 4): a normal MV demonstrated complete coaptation with no regurgitation when closed. Figure 4 Case 1: A Normal MV With Complete Coaptation; A to D (Peak Systole), E to H (End Diastole) Case 2 (Fig. 5): this MV showed mild regurgitation with relatively small annular dilation. Computational simulation indicated increased leaflet stress values and reduced contact pressure between the leaflets. Figure 5 Case 2: A Degenerative MV With Mild Regurgitation and Small Annular Dilation; A to D (Peak Systole), E to H (End Diastole) Case 3 (Fig. 6): a degenerative MV with large annular dilation demonstrated severe regurgitation by 3D Doppler TEE and the lesion corresponded to regions with no leaflet contact in the computational simulation. Figure 6 Case 3: A Degenerative MV With Severe Regurgitation and Large Annular Dilation; A to D (Peak Systole), E to H (End Diastole) Case 4 (Fig. 7): chordal rupture of this MV caused posterior leaflet prolapse inducing the regurgitant jet. Computational simulation demonstrated an extremely asymmetric and large stress distribution over the leaflets and lack of leaflet coaptation in the regurgitant region. Figure 7 Case 4: A Degenerative MV With Severe Regurgitation due to Ruptured Chordae; A to D (Peak Systole), E to H (End Diastole) Comparative studies of the normal MV (Case 1) and the pathological MV with ruptured chordae (Case 4) clearly demonstrated differences in annular reaction forces and chordal stresses (Fig. 8), and in the degree of leaflet coaptation (Fig. 9, Online Videos 5 and 6). Figure 8 Assessment of Annular Reaction Force and Chordal Stress Distribution; Normal MV (Case 1) Versus MV With Ruptured Chordae (Case 4) Figure 9 Contact Pressure Distribution Between the Leaflets; Normal MV (Case 1) Versus MV With Ruptured Chordae (Case 4) Although MV morphology obtained with 3D TEE image data may demonstrate relatively normal function with no regurgitation, the leaflets may be under extremely high stresses which can result in annular dilation and MV deterioration. Biomechanical information from computational simulation further provides information to help better understand MV pathophysiology. This novel computational strategy has the potential to predict pathophysiological alterations in MV structure, help cardiologists to quantitatively evaluate the extent and severity of MV pathology, and help surgeons to better understand MV dynamics before and following repair to determine more suitable patient-specific repair techniques.

Effects of Varus/Valgus rotation deficiency on the response of total knee prostheses

This study analysed the effect of the Varus/Valgus (V/V) rotation deficiency on the mechanical response of Total Knee Replacement (TKR) prostheses under compression loading test. 3D Finite Element (FE) models using ABAQUS program and an experimental apparatus are developed. Tow cases are considered: first, femoral component is allowed to move vertically only (Constrained Femoral Rotation – CFR); second, femoral component is allowed to move vertically and is unconstrained to (V/V) rotate (UNconstrained Femoral Rotation – UNCFR). Reaction force, displacement, contact area and stress distribution in the medial and lateral compartments have been investigated. The deficiency mobility is driven an increase of the stiffness prosthesis 16% at 3000 N, disequilibrium in the reaction force distribution between the medial and lateral compartment, increase of stress concentration and an increase of the contact area. These results depend on the contact geometry and the initial contact location.

A NEW STABILITY CRITERION FOR HUMAN SEATED TASKS WITH GIVEN POSTURES

In digital human modeling (DHM), the analysis of postural stability has five main goals: to determine if a posture is stable or unstable through an explicit criterion; to quantify the level of stability or provide a margin of stability that accounts for the height of the center of mass (COM) above the support plane(s); to be valid in the presence of externally applied forces and moments; be able to assess stability when multiple noncoplanar support planes exist, as is the case with seated postures; and to give insight into the support reaction force (SRF) distribution. To date, there is not a method for analyzing stability that can effectively meet each goal. This paper presents a new stability criterion and stability analysis that accomplishes each intended goal. The stability analysis is derived from the calculation of joint torque using the recursive Lagrangian dynamic formulation. A 56-degree-of-freedom (DOF) articulated digital human model is used to model seated postures to demonstrate the proposed stability criterion. Different given postures with different external load cases are presented.

사각에 따른 RC슬래브교의 반력특성 분석

본 연구에서는 2경간 연속 RC 슬래브교를 대상으로 차량 이동하중 시간이력해석을 수행하여 사각에 따른 받침의 반력분포 특성을 분석하였다. 계측값과 해석값의 비교를 통해 적용 시간이력해석방법을 검증하였으며, 사각을 매개변수로 판 해석을 수행한 결과, 둔각부 최외측 받침에 반력이 집중되며, 사각이 감소함에 따라(사교의 정도가 커질수록) 반력의 편차가 커져 둔각부에 반력의 크기가 증가하는 것으로 나타났다. 또한, 반력이 집중된 최외측 받침의 인접 받침에서는 사각 <TEX>$70^{\circ}$</TEX> 이하에서 부반력이 발생하는 것으로 분석되었다. 따라서 사각을 갖는 RC 슬래브교에서는 받침의 용량 산정 시 반력의 편차와 부반력 발생에 유의하여야 한다고 판단된다. The support reactions of two-span RC slab bridges with various skews are studied through the time history analysis for moving vehicles. Dynamic behaviors of bridges are evaluated by using the commercial FEM code and the bridge is modelled using shell elements. The analysis method is verified by comparing measured values and analysis results. Parametric analysis are performed for various skew angles. The bearing below the end slab with an obtuse angle shows the largest reaction forces. As the skew angle is reduced(a skew angle of <TEX>$90^{\circ}$</TEX> means a straight bridge without skew in this study), the distribution of reaction force is growing uneven and the largest reaction force is increased. In case of the model having skew angles under <TEX>$70^{\circ}$</TEX>, the bearing located near the bearing with the largest reaction force shows the uplift force. Thus, it is concluded that the bearing in RC slab bridges with skew should be selected carefully by considering the variation of reaction force and uplift force.

DEVELOPMENT OF AFFORDABLE OPTICAL BASED GAIT ANALYSIS SYSTEMS

This paper presents a review on the development of affordable optical based gait analysis systems at Institut Teknologi Bandung. The development started with a 2D inverse dynamic analysis of human gait using five linkages based on an experimental motion data. Using a simple system consist of a camera, LED markers and a PC, the position of the markers were obtained by capturing and processing digital images of markers attached to human body during motion. The marker positions data was then used for further kinematics and dynamic analyses. An in-house kinematic and kinetic software has been developed for this purpose. From the analyses, the spatiotemporal gait parameters such as stride-length, cadence, cycle-time, speed and joint angles can be obtained as well as forces and moments. In the second stage, the 2-D analysis was improved by using seven linkages to include the foot. Using this, the system has been able to analyze ankle angle, position of the centre of pressure and ground reaction force distribution. Currently, the development is continued further for a 3D dynamic analysis of human gait using two cameras and a PC. As an outcome of this development, a database of Indonesian normal gait was established. This result is the first data available for gait of Indonesian. It is hoped that the quantitative data provided by this system can help physicians to diagnose and plan the treatment for patients.

Idiosyncratic control of the center of mass in expert climbers

Here, we studied posture and movement coordination adopted by expert climbers. The investigation of such expertise might be of particular interest to gain understanding about the mechanisms underlying the biomechanical control of vertical quadrupedal locomotion. A novel custom setup was developed to analyze the motion of the center-of-mass (COM) and complementary information about the dynamic distribution of vertical reaction forces under the feet during climbing in nine elite climbers (EC) and nine control subjects. Two adaptive features were found in EC. First, unexpectedly they tended to maintain larger COM distances from the wall relative to controls, during both the static and dynamic phases of vertical motion (by ∼5 cm in both cases). Second, while the control subjects tended to restrain the lateral motion of the COM, all EC demonstrated systematic COM oscillations (∼1.3 times larger) associated with a significant alternating dynamic redistribution of the body weight between the limbs during the double support phase. The latter phenomenon likely reflects an adopted basic climbing strategy in experts. Furthermore, a convergence of the optimal solution towards a more diagonal climbing strategy in EC may shed light on the origin of the diagonal gait in primates and early hominids habituated to quadrupedal vertical locomotion.