$143 Chapter 22. Techniques and methods of posture and gait analysis [ • ] Gait regularity: measurement and significance B. Auvinet 1, A.S. Alix 2, D. Chaleil 3, M. Brun 2, E. Barrey 4. 1H@ital de Laval, 2Association Pdgase-Mayenne, SFacultd de Pharmacie d'Angers, 4INRA d'Evry, France Introduction: Gait is characterized by an intrinsic temporal and spatial variability, which are considered as an important measure of motor skill. Methods: We used a gait analysis system (adapted for routine practice) based onto 3 dimensional acceleration measurements close to the centre of gravity (Locometrix ® a trademark and patented process of Centaure Metrix [www.locometrix.com]. This technology was patented by the French National Research Institute of Agriculture.). Stride dynamic regularity (which measure step variability) was calculated from the cranial-caudal acceleration by means of an autocorrelation function. This method take into account both temporal and dynamic parameters in the sagital plane [1,2]. We collected gait recordings from 417 healthy adults and elderly people, and several pathological matched populations (coxarthrosis: n 43; gonarthrosis: n 31; Parkinson's disease: n 40; elderly fallers: n 20). Results: In the control group the regularity index was normally distributed and there was no significant difference due to gender or age until 69 y (mean value: 331±38); after 70 y there was a reduction of gait regularity in both genders (mean value: 311±29). There was a significant decrease in the regularity (increase of variability), for each pathology (coxarthrosis: 242±55; gonarthrosis: 271±63; Parkinson's disease: 224±75; fall: 191±56; p <0.001). Furthermore, the decrease of regularity was correlated to clinical indices: Lequesne's functional index in coxarthrosis (r 0.76, p < 0.05), and motor score in Parkinson's disease (r 0.59, p < 0.001). Conclusion: These results showed the feasibility to measure gait regularity in routine practice and the relationships with clinical index. The regularity measurement could be used for grading disability and rating efficiency of treatment. References [1] Auvinet B, Chaleil D, Barrey E. Accelerometric gait analysis for use in hospital outpatients. Rev Rhum [Engl. Ed.] 1999; 66(7 9): 389 97. [2] Auvinet B, Berrut G, Touzard C, Moutel L, Collet N, Chaleil D, Barrey E. Reference data for normal subjects obtained with an accelerometric device. Gait Posture 2002; 16(2): 124 34. [• High level information extracted from a kinematic sensor P. Barralon 1 , N. Noury 1 , N. Vuillerme 1. 1TIMC-IMAG UMR CWRS 5525 38700 La Tronche, France This work was conducted in TIMC laboratory in the framework of Health Smart Homes. The purpose is to maintain and supervise elderly or fragile people at home. Activity and autonomy levels are important criteria to evaluate the health of the patient. The time spent in each postural state (lying, sitting, and standing), the periods of walking and the number of postural transitions: sit-to-stand (StS), back-to-sit (BtS) give information about the patient's activity. The goal of the current study was to detect these activities using an unique sensor made of three accelerometers, attached to the chest. We will, first, describe how each algorithm (posture, walking period, postural transitions) works. Secondly, we will show the results on real data. Experimentation with six young individuals was so carried out. Each subject realized daily activities (walking, sitting, lying down .... ). For the validation of these three gait and posture analyses algorithms, an observer (engineer) recorded the type and time of each activity. Finally a comparison between these observations and the results of algorithms will be presented. The performance of the various algorithms will be discussed. [ • Effect of cardan angles sequences on the force value I. Benkhemis 1'2, M. Boucher 1, W. Bertucci 2, R. Taiar2. 1Laboratoire de M~canique des Solides Poitiers', 2Laboratoire d'Analyse des' Contraintes Mdcaniques Reims, France Introduction: Since the matrix product is not commutative, we have six possibilities to calculate the three dimonsional joint angle using the Euler/Cardan angles. The result is a difference between the rotation parameters [1]. The aim of this study is to determine the effect sequence Cardan angle of the joint force calculated for each sequence. Methods: The subject's unipodal gesticulation is recorded by a video system (SAGA 3RT) equipped with six cameras(50Hz). The reaction force at the right foot is calculated by inverse dynamic using the joint angles reload to the six Cardan angle sequences. These forces are compared to the one obtaibend by the second drivative of the mass center and considered as the theorical data. Results and discussion: Maximum differences between the theorical force and the reaction force obtained by inverse dynamic is 67.97N for sequence 1 (Rx, Ry, Rz), 86.36N for sequence 2 (Rx, Rz, Ry), 130.6N for sequence 3 (Ry, Rx, Rz), 190.5N for sequence 4 (Ry, Rz, Rx), 87.38 N for sequence 5 (Rz, Rx, Ry), 83.58 N for sequence 6 (Rz, Ry, Rx). The root mean square differences are 20.94N, 24.43N, 28.83N, 37.76N, 22.75N and 23.49N for respectively the sequence 1, 2, 3, 4, 5 and 6. Our results suggest that this difference results could explain by the sequence effect on the parameters rotation [2]. In the future study, we quanticate how the uncertainties and errors progress for each sequence to determinate improve the comparison between them. References [1] Karduna A.R. et al. Scapular kinematics: effects of altering the Euler angle sequence of rotations. J Biomech 2000; 33(3), 1063 1068. [2] McNair Peter J., Hewson David J., Dombroski Erik, Stanley Stephen N. Stiffness and passive peak force changes at the ankle joint: the effect of different joint angular velocities. Clin. Biom. 2002; 17, 536 540. [• Effect of skin movement artifact on knee kinematics during gait and cutting motions measured in-vivo D.L. Benoit 1'2, D.K. Ramsey a'4, M. Lamontagne 5'6, L. Xu 6, R Wretenberg 2'4, R Renstrrm 1'2. 1Institution for Surgical Sciences, Section of Sports Medicine, Karolinska Institute, Stockholm, Sweden; :Department o f Orthopaedics', Karolinska Hospital, Stockholm, 3 Sweden," Department of Physical Therapy, University of Delaware, 4 USA," Institution for Surgical Sciences, Section of Orthopaedics', 5 Karolinska Institute, Stockholm, Sweden," School o f Human 6 Kinetics, University of Ottawa, Ottawa, Canada; Department of Mechanical Engineering, University o f Ottawa, Ottawa, Canada Introduction: Skin movement artifact limits the ability to accurately 3D tibio-femoral kinematics using non-invasive techniques. Previous investigations into the error associated with skin movement artifact have had few subjects and/or been measured under conditions that may not represent healthy populations. The purpose of this study is