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SB'20, 45ème Congrès de la Société de Biomécanique, Metz, France, 26-/10/2020 - 28/10/2020; The present study was thus designed to test the hypothesis that different types of footwear could induce a change in mediolateral stability.

A bad fitted saddle may hurt or injure the horse’s back. It is an important challenge for saddle designers to understand how a saddle interacts with different back shapes. Fitting is usually assess...

Knee joint kinematics derived from multi-body optimisation (MBO) still requires evaluation. The objective of this study was to corroborate model-derived kinematics of osteoarthritic knees obtained using four generic knee joint models used in musculoskeletal modelling – spherical, hinge, degree-of-freedom coupling curves and parallel mechanism – against reference knee kinematics measured by stereo-radiography. Root mean square errors ranged from 0.7° to 23.4° for knee rotations and from 0.6 to 9.0 mm for knee displacements. Model-derived knee kinematics computed from generic knee joint models was inaccurate. Future developments and experiments should improve the reliability of osteoarthritic knee models in MBO and musculoskeletal modelling.

Assessing the functional ability depending on the prosthesis fitting of individuals with transfemoral amputation (TFA) is critical for overall rehabilitation and prosthetic care. Gait analysis could provide an overwhelming number of biomechanical parameters. We argue that margins of stability (MoS) could be critical indicators of TFA’s control strategy. A study revealed statistically larger MoS on the prosthetic limb when comparing medial-lateral MoS for six TFAs fitted with a socket-suspended prostheses and six able- bodied during treadmill walking (Hof et al. 2007). Another study showed limited and non-significant differences when comparing anterior-posterior MoS for ten TFA fitted with mechanical and microprocessor-controlled knees during walking overground (Prinsen et al. 2017). There is a need to report MoS more widely, particularly for TFA fitted with bone-anchored prosthesis as osseoperception should improve control. A single case study demonstrated that the load applied by bone-anchored prosthesis fitted with microprocessor-controlled was attenuated by 10-20% compared to mechanical knee (Frossard et al. 2013). However, the impact of these loading differences on the overall gait pattern, including medial-lateral MoS, remains unknown.

Few studies have focused on the effect of posture during sprint start. The aim of this study was to measure the effect of the modification of horizontal distance between the blocks during sprint start on three dimensional (3D) joint angular velocity. Nine trained sprinters started using three different starting positions (bunched, medium and elongated). They were equipped with 63 passive reflective markers, and an opto-electronic Motion Analysis1 system was used to collect the 3D marker trajectories. During the pushing phase on the blocks, norm of the joint angular velocity (NJAV), 3D Euler angular velocity (EAV) and pushing time on the blocks were calculated. The results demonstrated that the decrease of the block spacing induces an opposite effect on the angular velocity of joints of the lower and the upper limbs. The NJAV of the upper limbs is greater in the bunched start, whereas the NJAV of the lower limbs is smaller. The modifications of NJAV were due to a combination of the movement of the joints in the different degrees of freedom. The medium start seems to be the best compromise because it leads, in a short pushing time, to a combination of optimal joint velocities for upper and lower segments.

Estimation of Body Segment Inertia Parameters (BSIP) is a necessary step to perform dynamic analysis of human movement. As BSIPs cannot be directly measured, they are usually estimated using regressions derived from anthropometric tables (AT, e.g. Dumas et al. 2007). However, these tables are usually not adapted to atypical populations (children, elderly, obese, individuals with prostheses, etc.) that are classically of interest. Another option consists in estimating segments' volumes and in deriving their BSIPs using assumptions on their density (usually a constant uniform density). This option is of growing interest as the developments of low-cost 3D scanners yield to simple and accessible ways to obtain 3D body shapes (e.g. Peyer et al. 2015). However, there are still some issues to transform the measured external envelop into 3D shapes for each segment that are relevant for the human movement analysis, i.e. segmented and projected into local coordinate systems (LCS) according to anatomical definition and landmarks (e.g. Wu et al., 2005). Thus, this study aims at proposing a semi-automatic method (i.e. with minimal manual intervention) to estimate relevant BSIP from body scanner images. It is specifically dedicated to be used in the context a human movement analysis framework.

Background. To describe 3D shoulder joint movements, the International Society of Biomechanics (ISB) recommends using segment coordinate systems (SCSs) on the humerus, scapula and thorax, and joint coordinate systems (JCSs) on the shoulder. However, one of the remaining problems is how to define the zero angles when the arm is in an initial reference position. The aim of this paper is to compare various methods of determining the JCSs of the shoulder that make it possible to define the zero angles of the arm in the resting position. Methods. Able-bodied subjects performed elevation movements in the scapular plane, specifically neutral, internal and external rotations of the humerus. The initial humerus position (at the beginning of the arm movement) and range of motion were analysed for the purpose of clinical interpretation of arm attitude and movement. The following four different JCSs were explored: (1) the standard JCS, defined as recommended by the ISB, (2) a first aligned JCS, where the humerus SCS is initially aligned with the scapula SCS, (3) a second aligned JCS, where the opposite operation is performed and 4) a third aligned JCS, where both the humerus and the scapular SCS are initially aligned with the thorax SCS. Findings. The second aligned JCS was the only method that did not produce any exaggerated range of movement in either anatomical plane. Interpretation. Mathematical JCS alignment allows clearer clinical interpretation of arm attitude and movement.

The International Society of Biomechanics (ISB) has recommended a standardisation for the motion reporting of almost all human joints. This study proposes an adaptation for the trapeziometacarpal joint. The definition of the segment coordinate system of both trapezium and first metacarpal is based on functional anatomy. The definition of the joint coordinate system (JCS) is guided by the two degrees of freedom of the joint, i.e. flexion-extension about a trapezium axis and abduction-adduction about a first metacarpal axis. The rotations obtained using three methods are compared on the same data: the fixed axes sequence proposed by Cooney et al., the mobile axes sequence proposed by the ISB and our alternative mobile axes sequence. The rotation amplitudes show a difference of 9 degrees in flexion-extension, 2 degrees in abduction-adduction and 13 degrees in internal-external rotation. This study emphasizes the importance of adapting the JCS to the functional anatomy of each particular joint.

Biomechanical models have been proposed in order to simulate the surgical correction of spinal deformities. With these models, different surgical correction techniques have been examined: distraction and rod rotation. The purpose of this study was to simulate another surgical correction technique: the in situ contouring technique. In this way, a comprehensive three-dimensional Finite Element (FE) model with patient-specific geometry and patient-specific mechanical properties was used. The simulation of the surgery took into account elasto-plastic behavior of the rod and multiple moments loading and unloading representing the surgical maneuvers. The simulations of two clinical cases of hyperkyphosis and scoliosis were coherent with the surgeon's experience. Moreover, the results of simulation were compared to post-operative 3D measurements. The mean differences were under 5 degrees for vertebral rotations and 5 mm for spinal lines. These simulations open the way for future predictive tools for surgical planning.

38ième congrès de la Société de Biomécanique francophone, MARSEILLE, FRANCE, 04-/09/2013 - 06/09/2013; A tennis racket is characterised by three moments of inertia. The swingweight is measured about the axis perpendicular to the handle of the racket in the perpendicular plane of the frame, the twistweight is measured about the axis perpendicular to the handle of the racket in the plane parallel to the frame and the polar moment is measured about the long axis of the racket (Brody 2000). On an absolute basis, players are more sensitive to polar moment than to the other two moments of inertia (Brody 2000). The main advantage of the increase in the polar moment is to offer more stability against twisting of the racket head with off-axis ball impacts. However, there are no data in the literature investigating the relationship between racket polar moment and joint loads experienced by the tennis player under field conditions. This study aimed at investigating the influence of the racket polar moment on the upper limb joint moments and powers during tennis forehand drive.

International audience

39ème Congrès de la Société de Biomécanique, VALENCIENNES, FRANCE, 27-/08/2014 - 29/08/2014; Static optimisation is often used in musculoskeletal modelling to solve the muscular redundancy problem (Cheze et al. 2012). However, the activity of antagonist muscles (Vigouroux et al. 2007) and biarticular muscles (e.g. rectus femoris) (Modenese et al. 2011 ; Moissenet et al. 2014) is often misestimated. Otherwise, the EMG-to-force approach can be used but the number of muscles in the model needs to be reduced to fit the number of available EMGs (Lloyd and Besier 2003 ; Nikooyan et al. 2012 ). The aim of this study was to develop and evaluate during gait a computational framework allowing to introduce a set of EMG-base d muscular activations in a static optimisation procedure. This can be done through a multi-objective optimisation problem: minimising the sum of squared muscular activations and, for each muscle having an available EMG, tracking the EMG-based muscular activations

39ème Congrès de la Société de Biomécanique, Valenciennes, France, 27-/08/2014 - 29/08/2014; Previous study showed that kinematic patterns reveal very little variability over repeated tennis strokes for individual player (Knudson 1990). Sport media, however, regularly show difficulties encountered by elite athletes in being accustomed to new equipment, especially in tennis activity. The stability of the pattern would thus be altered by changes in racket specifications. During overhead motion, the shoulder complex has a predominant function as it funnels the energy generated by the lower limbs and trunk to the upper limb and then to the racket, through the so-called kinetic chain (Sciascia et al. 2012). The variability of shoulder kinematic patterns could thus be a key point in habituation to a new equipment. The aim of this study was to explore the variability of the humerothoracic joint kinematic pattern in a highly skilled player when serving with his own racket and with another one. It was hypothesised that the kinematic pattern would be more variable when serving with another racket than with the regular one

International audience

38ième congrès de la Société de Biomécanique francophone, MARSEILLE, FRANCE, 04-/09/2013 - 06/09/2013; In overhead activities, and particularly in tennis, themajority of the force required to propel the ball forwards is developed in the legs and trunk in a closed chain manner, funnelled through the scapulohumeral complex and transferred to the racket (Sciascia et al. 2012). Specific segment positions and motions are fundamental for an efficient linkage of multiple segments in such kinetic chain (Sciascia et al. 2012).Among the ideal nodes of the tennis serve, the coupled scapular retraction/arm rotation to achieve cocking in the scapular plane is recommended (Sciascia et al. 2012). The scapula is conflicting as it is required to provide both significant mobility through a large arc of motion and a stable base for arm function (McClure et al. 2012). These competing functions make the scapular region vulnerable to scapular dyskinesis. Such alterations in scapular motions are observed in up to two-thirds of overhead athletes' shoulder pathologies (Kibler and Thomas 2012). As a consequence, early evaluation of scapular kinematics is indicated to prevent the athlete's risk of shoulder injury, and potentially minimise the occurrence of such injury later in the player's career. Moreover, tennis is one of the overhead activities involving an implement, hence questioning the racket influence on scapular motions. The aim of this study was therefore to investigate the scapulothoracic kinematics during scaption in young tennis players when holding or not the tennis racket.

Soft tissue artefacts (STA) are one of the main contemporary problems in 3D motion analysis. They are known to strongly affect the joint kinematics assessment and several methods of compensation ha...

Joint forces and moments obtained from inverse dynamics are widely used in gait analysis. Four 3D inverse dynamic methods have been proposed in the literature either based on vectors and Euler angl...