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EVALUATION OF THE KINEMATIC ENERGY BY INERTIAL MEASUREMENT UNIT DURING THE GET-UP TEST Kevin Lepetit (1), Khalil Ben Mansour (1), Sofiane Boudaoud (1), Kiyoka Kinugawa-Bourron (2), Frédéric Marin (1) 1. Sorbonne Universités, Université de technologie de Compiègne, UMR CNRS 7338, Compiègne, France 2. Hôpital Pitié-Salpêtrière – Charles Foix (AP-HP), France

Introduction In the context of the human welfare and ageing well, the functional age should be an indicator of the homeostasis and of maintaining both the cognitive and mobility abilities. The mechanical energy expenditure during the get-up test would be a relevant parameter to estimate the functional age [1]. Despite of being an accurate tool to determine mechanical energy expenditure, the motion capture requires expensive equipment not always available in clinical routine. Onbody fixed devices as Inertial Measurement Units (IMU) would allow new low cost opportunity to track such body segment kinematics and deduce kinematic energy. Unfortunately, the drawbacks of IMUs are low accuracy of the velocity and position determination. The aims of this study are: (i) propose a solution that allows evaluating translational and angular velocities and the kinematic energy of the trunk during the get-up test with one IMU; (ii) validate this proposal with an optoelectronic motion capture system.

methods relative to the motion capture system were computed throughout the performed motion. The pvalue was used to determine the influence of the aging suit simulator on the maximum KE found with the IMU.

Results The results (Table 1) highlight that the DISP method has given the best results relatively to the others according to both nRMSE minimization and correlation maximization. The p-value is less than 0.01, showing the influence of the aging suit simulator on the maximum KE. Methods nRMSE (%) Correlation DI 8.12±3.54 0.97±0.02 DISP 1.98±0.45 1.00±0.00 KM 16.03±1.77 0.76±0.04 Table 1: nRMSE and correlations between the three methods and motion capture.

Methods

Discussion

Three proposed methods to obtain translational velocity of the trunk are compared during the get-up test with an optoelectronic capture system. The first method named Direct Integration (DI) used temporal integration of the acceleration from the IMU (Opal, APDM) placed on the trunk. To limit integration cumulative error, the sensor’s drift is considered as linear so that the signal is corrected with the deviation slope [2]. The second method named DISP is windowing of the DI method only during the get-up maneuver in order to integrate during a shorter period of time [3]. In the third method named Kinematic Method (KM), orientation information is integrated to a simple parameterized kinematic chain of the trunk to obtain the position and the velocity after derivation [2]. In order to quantify accuracies of the three previous methods, motion capture with eighteen cameras (T160, Vicon motion systems Inc., Oxford, UK) with passive markers is simultaneously performed and considered as the reference data. The angular velocity is obtained from the orientation quaternions and the inertial parameters using Dumas’ anthropometric model [4]. To evaluate the Kinematic Energy (KE) of the trunk using aforementioned parameters, we hypothesize that the CoM is assimilated to the IMU position. Forty getup were performed with and without aging suit simulator. The normalized root mean square errors (nRMSE) and the correlation coefficients for the three

The DISP seems to be an efficient method to obtain translational velocity from IMUs if the acquisition time is short. Moreover, the DI and the DISP methods are easier to be performed than the KM. The kinematic energy of the trunk by IMU is reliable and well correlated with reference data. Calibration method would be further investigated to improve it. The results are promising and allow further research to evaluate the functional age, especially for elderly people.

Acknowledgements This work has received support from “Agence National de la Recherche” ANR-11-IDEX-0004-02 under Idex “Sorbonne Universités” in the investments for the future program.

References 1. 2. 3. 4.

Wilson et al, J applied physiology, 95:1728-36, 2003. Lepetit et al, CMBEE, 18(1):1984-85, 2015 Li et al, J Biomech, 43:1640-43, 2010. Dumas et al, J Biomech, 40:543-553, 2007.

22nd Congress of the European Society of Biomechanics, July 10 - 13, 2016, Lyon, France