Improvement of musculoskeletal model inputs : adjustment of acceleration by dynamic optimisation

The knowledge of intrinsic dynamics in terms of joint torques and muscle tensions is of importance for clinical investigations. The common process is to solve a multibody inverse dynamic problem based on a set of iterative equations using noisy experimental data as guest. Body segment accelerations are usually assessed by double differentiation, a method well-known to amplify kinematic measurement noise. As a result, iterative equations propagate uncertainties leading to inconsistencies between measured external force and the rate of change of linear momentum. Recent studies addressed this residual force problem by adjusting mass distribution while they calculate force tensions or by dealing with acceleration computation. However, these different approaches were based on a least-square problem still leading to approximate intrinsic dynamics. The aim of this communication is to compute joint accelerations by solving a dynamic optimization problem. We will examine the effect of the optimal adjustment on joint torques and muscle tensions

MECHANICAL LOADING OF THE LUMBAR SPINE OF ELITE ROWERS WHILE ROWING FIXED AND SLIDING ERGOMETERS

Low back injury is common in rowers. This study compared compressive forces of the lumbar spine, while rowing on fixed and sliding ergometers. Fifteen elite male rowers with no history of serious low back injury rowed the Concept2 Fixed (C2F), Concept2 Sliding (C2S) and RowPerfect (RP) ergometers at 32 strokes/min while 3D motion and external force data were recorded. Inverse dynamics analysis was used to find net lumbar moment and a lumbar model used to model compressive forces acting at L4/L5. Compressive force was significantly larger on C2F, at the catch and for 45 % of the stroke. Rowing on the C2F ergometer places greater compressive stress on the lumbar spine

AN ALGORITHM TO COMPUTE ABSOLUTE 3D KINEMATICS FROM A MOVING MOTION ANALYSIS SYSTEM

INTRODUCTION: Recently, Colloud et al. showed the feasibility of using a moving motion analysis system to acquire three dimensional (3d) kinematics over a large volume. They placed a motion analysis system on a rigid rolling frame that followed the displacement of a known object. In this pilot study, Colloud et al. obtained accuracy similar to those report for motion analysis systems (Richards, 1999). As a result, the rolling system is accurate enough for capturing the local 3d kinematics. However, the expression of the kinematics in a global frame – i.e. the absolute kinematics – has not been assessed. Thus it is impossible to calculate spatial-temporal parameters (e.g. step length, step width, walking speed in gait analysis). The purpose of this study is to propose an algorithm for calculating the 3d global kinematic of a subject walking on a 40 m-long pathway. METHODS: One male participant (age: 21 yr, height: 170 cm, mass: 62 kg) equipped with 22 reflective markers performed five trials on 40 meters. He was followed by a rolling frame (4.4 × 4.0 × 2.5 m) with a 8-camera motion analysis system (T40 series, Vicon, Oxford, UK) sampled at 100 Hz. Forty-one reflective markers were placed every meter on the ground on an horizontal line using a tape measurer and a self levelling laser. The algorithm consists in three steps: (i) estimation of the kinematics from the camera frame (AL) to a local frame (Ai) using two markers (gi and gj) seen on the ground, (ii) expressed this local kinematics in a global frame (AG) and (iii) calculation of the roto-translation (iRj) from this current local frame (Ai) to the next local frame (Aj) before gi disappears. This last step requires three visible ground markers (gi, gj and gk). An elimination procedure that minimizes the norm of Frobenius is used until 50% of the image remained. The accuracy and precision of the reconstruction were evaluated as the deviation of reconstructed marker position relative to its reference and as the radius of the spheres of 95% confidence for the ground markers express in the global frame, respectively. RESULTS and DISCUSSION: The accuracy was up to 16 mm in antero-posterior direction but could reach 138 and 163 mm in lateral and vertical directions over the 40 m translation. The deviations differed in direction and magnitude between the trials. The precision was lower than the precision estimated with a rigid object (1.3 mm). Although their position was fixed in the global frame, the markers were shaking, in the worst case, in a sphere of 20 mm. The errors in marker position could be reduced with a reconstruction using at least three cameras. CONCLUSION: This algorithm is efficient for the analysis of human movement on horizontal ground. It allows the calculation of spatio-temporal parameters related to the performance in ecological environments over many cycles for walking and many sports (e.g. running) REFERENCES: Colloud, F., Chèze, L., Andrè, N., Bahuaud, P. (2008). An innovative solution for 3D kinematics measurement for large volume. Journal of Biomechanics, 41(S1), S57. Richards, J., 1999. The measurement of human motion: A comparison of commercially available systems. Human Movement Science, 18, 589–602. Acknowledgement: The financial support of Région Rhône-Alpes (Projet Emergence) and Région Poitou-Charentes--European Union (CPER 2007-2013) is gratefully acknowledged

AN ORIGINAL INVERSE KINEMATICS ALGORITHM FOR KAYAKING

For some sports, e.g. kayaking and rowing, ecological conditions represent a challenge for collecting three-dimensional kinematics. The lower-limbs are partially hidden by the boat and motion analysis systems used in laboratory are not suitable for outdoor and on-water measurements. An inverse kinematics (IK) approach has been proposed where a few tasks would be measured by inertial sensors or inclinometers (Begon & Sardain, 2007). However, due to the lack of actual kinematics, the authors could not assess its reliability. The purpose of this study is to assess the accuracy of this IK algorithm by comparison with a standard algorithm of global optimization

International Society of Biomechanics in Sport March Newsletter 2015

IN THIS ISSUE: Message from the Editor, Preview of ISBS 2015, Poitiers, ISBS Student Mentor Program 2015,ISBS Student Mini Research Grant, ISBS Student Development Profile, Call for ISBS Awards, Hans Gros Emerging Researcher 2015, ISBS Practitioner Profile, ISBS Membership Renewal, Call for bids for hosting ISBS, ISBS Lab Profile, Call for ISBS Election, ISBS Sponsors, ISBS Officer

International Society of Biomechanics in Sport October Newsletter 2015

IN THIS ISSUE: Message from the President, ISBS 2015 Post Conference Report, Student Mini Research Grant Reports, ISBS Awards 2015, Call for ISBS Awards 2016, Report of Student Mentoring Program, Short Communications, ISBS Sponsors, Introducing Biomch-V, C-Motion Group Meetin

Effect of stroke rate on paddle tip path in kayaking

In kayaking, performance depends on stroke rate and propulsive force. On water, only partial blade kinematics and kinetics can be measured. Our objective is to assess, using an instrumented ergometer, the stroke rate effect (from 50 to 110 strokes per min) in 14 elite paddlers. The local blade path is measured and then expressed in an absolute frame of reference by simulating the on-water kinematics. Inter-stroke reproducibility of the paddle tip path is assessed by a multiple correlation coefficient. Kinematic and kinetic parameters are putted in relation with stroke rate. Whatever the stroke rate, blade paths are reproducible. However, the duration and the anteroposterior displacement of the blade in the pull phase decrease while catch and exit phases remain unchanged

Kinematics of the lumbar muscles in rowing: a preliminary study

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