Xuguang Wang

Comparison of global and joint-to-joint methods for estimating the hip joint load and the muscle forces during walking.

A three-dimensional musculoskeletal model of the lower limb was developed to study the influence of biarticular muscles on the muscle force distribution and joint loads during walking. A complete walking cycle was recorded for 9 healthy subjects using the standard optoelectronic motion tracking system. Ground contact forces were also measured using a 6-axes force plate. Inverse dynamics was used to compute net joint reactions (forces and torques) in the lower limb. A static optimization method was then used to estimate muscle forces. Two different approaches were used: in the first one named global method, the biarticular muscles exerted a torque on the two joints they spanned at the same time, and in the second one called joint-by-joint method, these biarticular muscles were divided into two mono-articular muscles with geometrical (insertion, origin, via points) and physiological properties remained unchanged. The hip joint load during the gait cycle was then calculated taking into account the effect of muscle contractions. The two approaches resulted in different muscle force repartition: the biarticular muscles were favoured over any set of single-joint muscles with the same physiological function when using the global method. While the two approaches yielded only little difference in the resultant hip load, the examination of muscle power showed that biarticular muscles could produce positive work at one joint and negative work at the other, transferring energy between body segments and thus decreasing the metabolic cost of movement.

A 3D reconstruction method of the body envelope from biplanar X-rays: Evaluation of its accuracy and reliability

The aim of this study was to propose a novel method for reconstructing the external body envelope from the low dose biplanar X-rays of a person. The 3D body envelope was obtained by deforming a template to match the surface profiles in two X-rays images in three successive steps: global morphing to adopt the position of a person and scale the template׳s body segments, followed by a gross deformation and a fine deformation using two sets of pre-defined control points. To evaluate the method, a biplanar X-ray acquisition was obtained from head to foot for 12 volunteers in a standing posture. Up to 172 radio-opaque skin markers were attached to the body surface and used as reference positions. Each envelope was reconstructed three times by three operators. Results showed a bias lower than 7mm and a confidence interval (95%) of reproducibility lower than 6mm for all body parts, comparable to other existing methods matching a template onto stereographic photographs. The proposed method offers the possibility of reconstructing body shape in addition to the skeleton using a low dose biplanar X-rays system.

Methods for determining hip and lumbosacral joint centers in a seated position from external anatomical landmarks

A global coordinate system (GCS) method is proposed to estimate hip and lumbosacral joint centers (HJC and LSJC) from at least three distances between joint center of interest and target anatomic landmarks (ALs). The distances from HJC and LSJC to relevant pelvis and femur ALs were analyzed with respect to usual pelvis and femur scaling dimensions. Forty six pelves and related pairs of femurs from a same sample of adult specimens were examined. The corresponding regression equations were obtained. These equations can be used to estimate HJC and LSJC in conditions where a very limited number of ALs are available: for example, during seated posture analysis as performed in the automotive industry. Compared to currently existing HJC and LSJC methods from ALs, the proposed method showed better results with an average error less than 11 mm.

Three-Dimensional Rotations of the Scapula During Arm Abduction: Evaluation of the Acromion Marker Cluster Method in Comparison With a Model-Based Approach Using Biplanar Radiograph Images

Noninvasive methods enabling measurement of shoulder bone positions are paramount in clinical and ergonomics applications. In this study, the acromion marker cluster (AMC) method is assessed in comparison with a model-based approach allowing scapula tracking from low-dose biplanar radiograph images. Six healthy male subjects participated in this study. Data acquisition was performed for 6 arm abduction positions (0°, 45°, 90°, 120°, 150°, 180°). Scapula rotations were calculated using the coordinate systems and angle sequence was defined by the ISB. The comparison analysis was based on root mean square error (RMSE) calculation and nonparametric statistical tests. RMSE remained under 8° for 0° to 90° arm abduction and under 13.5° for 0° to 180° abduction; no significant differences were found between the 2 methods. Compared with previous works, an improved accuracy of the AMC approach at high arm abduction positions was obtained. This could be explained by the different sources of data used as the gold standard.

Arm postural anticipation for rotating a spherical object

Muscle forces during locomotion are often predicted using static optimisation and SQP. SQP has been criticised for over-estimating force magnitudes and under-estimating co-contraction. These problems may be related to SQPs difficulty in locating the global minimum to complex optimisation problems. Algorithms designed to locate the global minimum may be useful in addressing these problems. Muscle forces for 18 flexors and extensors of the lower extremity were predicted for 10 subjects during the stance phase of running. Static optimisation using SQP and two random search (RS) algorithms (a genetic algorithm and simulated annealing) estimated muscle forces by minimising the sum of cubed muscle stresses. The RS algorithms predicted smaller peak forces (42% smaller on average) and smaller muscle impulses (46% smaller on average) than SQP, and located solutions with smaller cost function scores. Results suggest that RS may be a more effective tool than SQP for minimising the sum of cubed muscle stresses in static optimisation.Digital human models (DHM) are more and more used in ergonomic applications. A key issue for researchers is yet to improve the DHM ability to interact with their environment, i.e. to be able to predict the motions of prehension and manipulation of objects. This experimental study focused on the influence of the task to perform [manipulation of the object] on the prehension postures. It aimed to better understand its influence on both the grasping posture and the variability of this posture.

Fingertip finite element modelling - on choosing the right material property

Human hand models able to reproduce fingertip deformation are key elements in ergonomics applications associated to grasping and manipulation tasks. The mechanical response of fingertip soft tissues is strongly nonlinear and depends both on material properties and on geometry. Most of the existing models are based on hyperelastic laws (Wu 2002; Chamoret 2013); however, there is no consensus on whether using anisotropy or isotropy (only Chamoret used an anisotropic law). Fingertip complex shape could be simplified by idealised geometries such as ellipsoids (Wu 2002). However, the influence of many modelling parameters on the global response still needs to be assessed. Thus, the current work focuses on fingertip modelling and studies the variation of the model response to compression simulation at different angles and with varying geometrical parameters.

Dynamics of sit-to-stand motions: effect of seat height, handle use and asymmetrical motions

Rising from a seat is a common task in our daily life. It may also be a challenging task as it consists in elevating the centre of mass (CoM) while passing from a stable seated posture to a less stable standing posture. This motion has been extensively studied in the past: see Janssen et al. (2002) for a review. However, two main drawbacks appear in the literature: (1) there are very few studies focusing on the effect of the use of a handle to facilitate this motion – only O’Meara and Smith (2006) to our knowledge – and (2) no study reports data on sit-tostand motions out of the sagittal plane, although it is a classical type of sit-to-stand condition (e.g. rising while seated on a table, car egress motions, etc.). Therefore, this study focuses on the influence of these parameters on the net joint torques and contact reaction forces developed during sit-to-stand motions.

A Markerless Method for Personalizing a Digital Human Model from a 3D Body Surface Scan

Digital Human Models (DHM) are used for ergonomic design of products. For instance, vehicle ingress/egress motions are simulated for assessing vehicle accessibility. In order to validate simulations, experiments are often needed implying motion capture and motion reconstruction using a DHM. The first step for motion reconstruction is to create a personalized DHM respecting the anthropometric dimensions of the volunteer performing the task. However creating a personalized DHM from external body shape is not straight forward, because the internal skeleton has to be identified from external body shape. Here we propose a four-step method for generating a personalized DHM which matches a 3D scan. The first step is to clean the scan data and to prepare a DHM and a third body surface template. Then, thanks to the use of the third common body template, the correspondence between the DHM and scan surface points is established, making it possible to calculate the transformation parameters by kriging. From estimated position of joint centers, the internal skeleton is scaled and positioned from a known reference posture to the scan position. The third step is then to attach the surface points to their corresponding skeletal segments. The last step is to check and correct the attached skin points around some joints so as to respect the skin to segment structure specific to a DHM. Compared to the method used in the past by manually adjusting a DHM on calibrated photos of several points of views; the proposed method is operator independent and much less time consuming.

A preliminary study on the realism of digital human manikins used for ergonomics simulation.

Digital human models (DHM) are used for ergonomics assessment of a product or a workplace in its early phase of development. Differently sized manikins are simulated to provide designs that accommodate with a large range of a target population (Chaffin 2005). They are also used in ergonomics research for posture/movement analysis, and personalised manikins should be defined. The geometric model of a DHM consists of two distinguished parts: an external body shape and an internal articulated linkage representing the skeleton. To build a subject-specific manikin, a set of anthropometric measurements are first collected from a volunteer under study. The manikin’s external shape and internal linkage are estimated as a function of these external inputs. For instance, Human Builder, one of the most widely used DHMs, requires up to 70 anthropometric measurements such as stature, sitting height, and weight for creating a manikin. In practice, not all required anthropometric measures are available. The missing parameters necessary for manikin generation are automatically estimated from a chosen anthropometric database. A similar module can be found in RAMSIS, another DHM widely used in automotive packaging. However, few studies have been published for verifying the realism of these personalised manikins, in particular their internal skeleton linkage (Zhang et al. 2004). Thanks to recent advances in medical imaging, data of both external body shape and internal skeleton are becoming available. Therefore, this study aimed to verify how good these personalised manikins are, especially in terms of the joint location.

Hip joint centre location from anatomical landmarks for automotive seated posture reconstruction

Hip joint centre location from anatomical landmarks for automotive seated posture reconstruction J. Peng, X. Wang, L. Denninger, J. Panda & S. Van Sint Jan a Universite de Lyon, F-69622, Lyon, France b IFSTTAR, LBMC, UMR_T9406, Bron, France c Universite Lyon 1 Villeurbanne, Villeurbanne, France d PSA Peugeot-Citroen, Sochaux, France e Laboratory of Anatomy, Biomechanics and Organogenesis (LABO) of Universite Libre de Bruxelles (ULB), 1000 Bruxelles, Belgium f Department of Orthopaedics, University of Lubumbashi, Lubumbashi, Democratic Republic of the Congo Published online: 07 Aug 2013.