- Email: [email protected]
P058 Biomechanical analysis of hip and ankle strategies during fast forward upper trunk bending
BIOMECHANICAL STRATEGIES DURING
ANALYSIS OF HIP AND ANKLE FAST FORWARD UPPER TRUNK BENDING A.V. Alexandrov’, A.A. Frolov’, J. Massion ‘Institute of Higher Nervous Activity and Neurophysiology of Russian Academy of Sciences, Moscow, Russia *Laboratory of Neurobiology and Movements, CNRS, Marseille, France INTRODUCTION: Upper trunk bending in human is accompanied by lower segments’ movement in the opposite direction (kinematic synergy’) stabilizing the center of pressure (CP) and center of gravity (CC) within the support limits. The goal of the study is to understand from biomechanical point of view how the implementation of kinematic synergies aimed at two simultaneous behavioral goals (bending per se and equilibrium maintenance) is achieved. METHODS: The research includes a theoretical analysis using a two-joint (hip and ankle) model of the body and an analysis of the data obtained in 16 subjects. Subjects performed fast forward bending, standing on the force platform or on a narrow beam (5 cm width). Kinematic recordings by ELITE system and force platform recordings were performed. Forward bending was decomposed into two dynamically independent synergies. In the plane of two joint angles, each synergy represents the movement along one of two eigenvectors of the motion equation and is accompanied by synergistic changes in hip and ankle joint torques. Such movement is termed below “eigenmovement”. The optimal coordination between two eigenmovements that provides bending without any CP displacement (i.e., “without any equilibrium disturbance”) was obtained by solution of the motion equation. Thereafter optimal bending was compared with experimentally observed. RESULTS: Two eigenmovements were identified differing largely by their kinematics, dynamics and inertial properties. In the low inertial eigenmovement, torque and angular changes were dominant in the hip joint whereas in the high inertial eigenmovement these changes predominated in the ankle joint. Therefore, these eigenmovements were termed “hip” and “ankle” eigenmovements. Hip eigenmovement mainly relates to hip flexion while ankle eigenmovement -- to the whole body rotation around the ankle joint. Theoretical analysis showed that optimal bending can be performed in human only when the movement is close to hip eigenmovement (prime eigenmovement). Ankle eigenmovement in the optimal bending starts earlier and contributes much less into movement kinematics than hip eigenmovement. Similar properties of both eigenmovements were observed in experimental data. DISCUSSION: In spite of weak contribution into the total kinematics, anticipatory ankle eigenmovement is important to compensate CC and CP shifts caused by prime hip eigenmovement. The results clarify from biomechanical point of view the EMG patterns usually observed in forward bending*. They provide biomechanical background to the different strategies (“hip and ankle”) used by subjects in response to postural perturbations’. CONCLUSION: The results suggest that two eigenmovements can be treated as functionally independent synergies aimed at different goals: bending per se (prime hip eigenmovement) and equilibrium maintenance (associated ankle eigenmovement). REFERENCES: LBabinski J. Rev Neurol., 7, 806-816, 1899. 2.Crenna et al., Exp. Brain Res. 65, 538-548, 1967. J.Nashneret al., Behav. Brain Sci., 8, 135172. ACKNOWLEDGEMENTS: The work was supported by the Russian Foundation of Basic Research(9604-49412) and by INTAS-RFBR 95-1327 CORRESPONDENCE: Alexei Alexandrov, IVND RAN, Butlerov str., 5A. 117865, Moscow, Russia. Tel: 7 (095) 334 77 49, Fax: 7 (095) 338 85 00. [email protected]
84
II”’ Conference
RECONSTRUCTION OF 7 DoF HUMAN ARM KINEMATICS FROM POLHEMUS FASTRAK RECORDINGS E.V. Biryukova’, A. Roby-Brami’. M. Mokhtari’. A.A. Frolov’ ‘Institute of Higher Nervous Activity and Neurophysiology of Russian Academy of Sciences, Moscow, Russia, 2 NSERM U483, Paris, France INTRODUCTION: The goal of this study was to elaborate a method of calculation of 7 DoF human arm joint angles from the Polhemus Fastrak Space Tracking System (STS) recordings. Precise and redundant STS recordings gives the possibility to reconstruct the positions of the anatomical axes of rotations, the angles of rotations about them and the geometrical parameters of the joints. METHODS: Four markers located on the hand, forearm, humerus and acromion were used. Three coordinates of the origins of marker’s reference frames as well as Cardanic angles of marker’s axes rotations relative to stationary axes constituted the STS recordings. We used a biomechanical model of the human arm consisting of three rigid links connected by ideal joints and having 7 degrees of freedom (DoF): 3 DoF in the shoulder joint, 2 DoF both in the elbow and in the wrist joints. To reconstruct the joint angles corresponding to each DoF we have first determined the positions of the axes of rotation in the marker’s reference frames. The method of calculations of position of joint centers and axes of rotations (Biryukova et al., 1996) was based on the least square method. The joint angles relative the determined axes of rotations were calculated under the assumption that the shoulder joint is a ball joint with fixed center of rotation and the elbow and wrist joints have two independent crossing axes of rotations each. The acceleration of the hand was calculated by solving the direct kinematics problem on the base of the reconstructed joint angles. The accuracy of the proposed method was estimated by the comparison of the calculated accelemtion with the data of 3D accelerometer mounted on the hand. RESULTS: The good agreement was found between the calculated and registered acceleration of the hand. By contrast, there was a deviation about l-2 cm between the calculated and registered coordinates markers. The error was found mainly due to the essential dependence of the position of the axis of flexionextension in the elbow from the pronation of the forearm. In the frames of the rigid body assumption when we have to fix the axes of rotation relative to the segments this error seems to be inevitable. The positions of the other axes of rotation of the arm were found to have small inter-motion deviations, There is reasonable agreement of the calculated positions of the axes with the published data (e.g. Youm et al.. 1979). DISCUSSION: The described calculations of human arm kinematics have the natural sources of errors: 1) the displacements of markers relative to segments due to skin displacements and muscle contractions; 2) the possible changes of joint centers and axes of rotation during the movement. The values of these errors can be considered as a kind of estimation of the accuracy of the rigid body assumption. Our method is based on the minimization of the summary effect of these errors during the movement. As distinct from another approaches applying this method for the set of markers (Veldpaus et al., 1988; Woltring et al., 1985) we applied it for all period of motion. It can be considered therefore as some kind of smoothing of the recordings. CONCLUSION: The calculated errors of the position of the hand in the frames of the rigid body assumption are rather small. It is possible to use the proposed method for the reconstruction of the multijoint arm kinematics from the STS recordings. REFERENCES: 1. Biryukova et al., International Symposium on 3-D Analysis of Human Movement, Grenoble, 1-3 July 1996. 2. Veldpaus et al.. J.Biomech., 21. 45-54, 1988. 3. Woltring et al., J.Biomech., 18, 379-389.1985. 4. Youm et al., J.Biomech., 12, 245-255, 1979. ACKNOWLEDGEMENTS: The work is supported by EEC contract ERB-CHRX-CT93-0266 and by INSERM CORRESPONDENCE: Elena Biryukova, fVND RAN, Butlerov str., 5A, 117865, Moscow, Russia. Tel: 7 (095) 334 42 31, Fax: 7 (095) 338 85 00. [email protected]
of the ESB. July 8-l 1 98, Toulouse. France
ANALYSIS OF HIP AND ANKLE FAST FORWARD UPPER TRUNK BENDING A.V. Alexandrov’, A.A. Frolov’, J. Massion ‘Institute of Higher Nervous Activity and Neurophysiology of Russian Academy of Sciences, Moscow, Russia *Laboratory of Neurobiology and Movements, CNRS, Marseille, France INTRODUCTION: Upper trunk bending in human is accompanied by lower segments’ movement in the opposite direction (kinematic synergy’) stabilizing the center of pressure (CP) and center of gravity (CC) within the support limits. The goal of the study is to understand from biomechanical point of view how the implementation of kinematic synergies aimed at two simultaneous behavioral goals (bending per se and equilibrium maintenance) is achieved. METHODS: The research includes a theoretical analysis using a two-joint (hip and ankle) model of the body and an analysis of the data obtained in 16 subjects. Subjects performed fast forward bending, standing on the force platform or on a narrow beam (5 cm width). Kinematic recordings by ELITE system and force platform recordings were performed. Forward bending was decomposed into two dynamically independent synergies. In the plane of two joint angles, each synergy represents the movement along one of two eigenvectors of the motion equation and is accompanied by synergistic changes in hip and ankle joint torques. Such movement is termed below “eigenmovement”. The optimal coordination between two eigenmovements that provides bending without any CP displacement (i.e., “without any equilibrium disturbance”) was obtained by solution of the motion equation. Thereafter optimal bending was compared with experimentally observed. RESULTS: Two eigenmovements were identified differing largely by their kinematics, dynamics and inertial properties. In the low inertial eigenmovement, torque and angular changes were dominant in the hip joint whereas in the high inertial eigenmovement these changes predominated in the ankle joint. Therefore, these eigenmovements were termed “hip” and “ankle” eigenmovements. Hip eigenmovement mainly relates to hip flexion while ankle eigenmovement -- to the whole body rotation around the ankle joint. Theoretical analysis showed that optimal bending can be performed in human only when the movement is close to hip eigenmovement (prime eigenmovement). Ankle eigenmovement in the optimal bending starts earlier and contributes much less into movement kinematics than hip eigenmovement. Similar properties of both eigenmovements were observed in experimental data. DISCUSSION: In spite of weak contribution into the total kinematics, anticipatory ankle eigenmovement is important to compensate CC and CP shifts caused by prime hip eigenmovement. The results clarify from biomechanical point of view the EMG patterns usually observed in forward bending*. They provide biomechanical background to the different strategies (“hip and ankle”) used by subjects in response to postural perturbations’. CONCLUSION: The results suggest that two eigenmovements can be treated as functionally independent synergies aimed at different goals: bending per se (prime hip eigenmovement) and equilibrium maintenance (associated ankle eigenmovement). REFERENCES: LBabinski J. Rev Neurol., 7, 806-816, 1899. 2.Crenna et al., Exp. Brain Res. 65, 538-548, 1967. J.Nashneret al., Behav. Brain Sci., 8, 135172. ACKNOWLEDGEMENTS: The work was supported by the Russian Foundation of Basic Research(9604-49412) and by INTAS-RFBR 95-1327 CORRESPONDENCE: Alexei Alexandrov, IVND RAN, Butlerov str., 5A. 117865, Moscow, Russia. Tel: 7 (095) 334 77 49, Fax: 7 (095) 338 85 00. [email protected]
84
II”’ Conference
RECONSTRUCTION OF 7 DoF HUMAN ARM KINEMATICS FROM POLHEMUS FASTRAK RECORDINGS E.V. Biryukova’, A. Roby-Brami’. M. Mokhtari’. A.A. Frolov’ ‘Institute of Higher Nervous Activity and Neurophysiology of Russian Academy of Sciences, Moscow, Russia, 2 NSERM U483, Paris, France INTRODUCTION: The goal of this study was to elaborate a method of calculation of 7 DoF human arm joint angles from the Polhemus Fastrak Space Tracking System (STS) recordings. Precise and redundant STS recordings gives the possibility to reconstruct the positions of the anatomical axes of rotations, the angles of rotations about them and the geometrical parameters of the joints. METHODS: Four markers located on the hand, forearm, humerus and acromion were used. Three coordinates of the origins of marker’s reference frames as well as Cardanic angles of marker’s axes rotations relative to stationary axes constituted the STS recordings. We used a biomechanical model of the human arm consisting of three rigid links connected by ideal joints and having 7 degrees of freedom (DoF): 3 DoF in the shoulder joint, 2 DoF both in the elbow and in the wrist joints. To reconstruct the joint angles corresponding to each DoF we have first determined the positions of the axes of rotation in the marker’s reference frames. The method of calculations of position of joint centers and axes of rotations (Biryukova et al., 1996) was based on the least square method. The joint angles relative the determined axes of rotations were calculated under the assumption that the shoulder joint is a ball joint with fixed center of rotation and the elbow and wrist joints have two independent crossing axes of rotations each. The acceleration of the hand was calculated by solving the direct kinematics problem on the base of the reconstructed joint angles. The accuracy of the proposed method was estimated by the comparison of the calculated accelemtion with the data of 3D accelerometer mounted on the hand. RESULTS: The good agreement was found between the calculated and registered acceleration of the hand. By contrast, there was a deviation about l-2 cm between the calculated and registered coordinates markers. The error was found mainly due to the essential dependence of the position of the axis of flexionextension in the elbow from the pronation of the forearm. In the frames of the rigid body assumption when we have to fix the axes of rotation relative to the segments this error seems to be inevitable. The positions of the other axes of rotation of the arm were found to have small inter-motion deviations, There is reasonable agreement of the calculated positions of the axes with the published data (e.g. Youm et al.. 1979). DISCUSSION: The described calculations of human arm kinematics have the natural sources of errors: 1) the displacements of markers relative to segments due to skin displacements and muscle contractions; 2) the possible changes of joint centers and axes of rotation during the movement. The values of these errors can be considered as a kind of estimation of the accuracy of the rigid body assumption. Our method is based on the minimization of the summary effect of these errors during the movement. As distinct from another approaches applying this method for the set of markers (Veldpaus et al., 1988; Woltring et al., 1985) we applied it for all period of motion. It can be considered therefore as some kind of smoothing of the recordings. CONCLUSION: The calculated errors of the position of the hand in the frames of the rigid body assumption are rather small. It is possible to use the proposed method for the reconstruction of the multijoint arm kinematics from the STS recordings. REFERENCES: 1. Biryukova et al., International Symposium on 3-D Analysis of Human Movement, Grenoble, 1-3 July 1996. 2. Veldpaus et al.. J.Biomech., 21. 45-54, 1988. 3. Woltring et al., J.Biomech., 18, 379-389.1985. 4. Youm et al., J.Biomech., 12, 245-255, 1979. ACKNOWLEDGEMENTS: The work is supported by EEC contract ERB-CHRX-CT93-0266 and by INSERM CORRESPONDENCE: Elena Biryukova, fVND RAN, Butlerov str., 5A, 117865, Moscow, Russia. Tel: 7 (095) 334 42 31, Fax: 7 (095) 338 85 00. [email protected]
of the ESB. July 8-l 1 98, Toulouse. France