Determination of the 3D Human Spine Posture from Wearable Inertial Sensors and a Multibody Model of the Spine

[Abstract] Determination of spine posture is of great interest for the effective prevention, evaluation, treatment and evolution monitoring of spinal disorders. Limitations of traditional imaging systems, including cost, radiation exposure (for X-ray based systems), projection volume issues and subject positioning requirements, etc., make non-invasive motion assessment tools effective alternatives for clinical and non-clinical use. In this work, a procedure was developed to obtain a subject-specific multibody model of the spine using either inertial or optical sensors and, based on this multibody model, to estimate the locations and orientations of the 17 vertebrae constituting the thoracolumbar spine. The number and calibration of the sensors, angular offsets, scaling difficulties and gender differences were addressed to achieve an accurate 3D-representation of the spine. The approach was validated by comparing the estimated positions of the sensors on 14 healthy subjects with those provided by an optical motion capture system. A mean position error of lower than 12 mm was obtained, thus showing that the proposed method can offer an effective non-invasive tool for the assessment of spine posture.This work was funded by the Spanish MCI under project PGC2018-095145-B-I00, co-financed by the EU through the EFRD program, and by the Galician Government under grant ED431C2019/29 and under grant IN853B-2018/02Xunta de Galicia; ED431C2019/29Xunta de Galicia; IN853B-2018/0

Biomechanical models for human gait analyses using inverse dynamics formulation

The main goal of this work is to present planar biomechanical multibody models, suitable to be used in inverse dynamic analyses. The proposed approach is straightforward and computationally efficient for the study of different human gait scenarios for normal and pathological. For this, a biomechanical model of the lower limb of the human body was developed. The biomechanical model consists of three bodies (thigh, calf and foot), corresponding to relevant anatomical segments of lower limb. These three rigid bodies are connected by revolute joints and described by eight natural coordinates, which are the Cartesian coordinates of the basic points located at the joints (hip, knee, ankle, metatarsal- phalangeal). The anthropometric dimensions of the model correspond to those of a normal male of 1.77 m and 80.0 kg. The total biomechanical system encompasses 5 degrees of freedom: 2 degrees if freedom for hip trajectory, 1 degree of freedom for hip flexion-extension motion, 1 degree of freedom for knee flexion-extension and 1 degree of freedom for ankle plantarflexion- dorsiflexion. The developed model was applied to solve an inverse dynamics problem of human motion. Therefore, the main objective of this simulation is to determine the joint moments-of- force and the joint reaction forces during an entire gait cycle, in order to compare with literature data.Fundação para a Ciência e a Tecnologia (FCT

Flexible multibody systems modeling for a dynamic analysis with geometric nonlinearity

Las herramientas de simulación en el análisis de sistemas multicuerpo son un campo de investigación vivo y abierto, que permite la reducción de tiempos y costes en el proceso de diseño de sistemas mecánicos. Durante los últimos años, los autores han desarrollado un método de análisis de sistemas multicuerpo con componentes rígidos y flexibles, basado en la aproximación de sistema de referencia móvil. En este tipo de métodos se usan coordenadas que separan el movimiento de gran amplitud del mecanismo, del de pequeña amplitud, debido a la deformación de componentes. Son muy eficientes y están muy extendidos, pero son válidos cuando los componentes flexibles experimentan pequeñas deformaciones. Con componentes suficientemente flexibles trabajando a velocidades elevadas deja de ser admisible la hipótesis de pequeñas deformaciones y aparecen efectos de segundo orden que influyen decisivamente en la predicción del movimiento del sistema. Este trabajo estudia la modelización del fenómeno de rigidización geométrica en el análisis de sistemas multicuerpo con componentes flexibles, con un doble objetivo, la determinación precisa del estado tensional en componentes y la consecución de tiempo real en la simulación de este tipo de sistemas en ordenadores convencionales. Para ello se analiza un sistema en el que esta no linealidad elástica geométrica es significativa y se ensayan dos propuestas basadas, respectivamente, en el aumento del número de modos axiales y en la consideración del movimiento axial causado por la flexión o “foreshortening”. Dichas propuestas permiten mejorar la precisión y la eficiencia de las formulaciones actuales.Peer Reviewe

Energy Expenditure Estimation During Crutch-Orthosis-Assisted Gait of a Spinal-Cord-Injured Subject

[Abstract] Determination of muscle energy expenditure by computer modeling and analysis is of great interest to estimate the whole body energy consumption, while avoiding the complex character of in vivo experimental measurements for some subjects or activities. In previous papers, the authors presented optimization methods for estimating muscle forces in spinal-cord-injured (SCI) subjects performing crutch-assisted gait. Starting from those results, this work addresses the estimation of the whole body energy consumption of a SO subject during crutch-assisted gait using the models of human muscle energy expenditure proposed by Umberger and Bhargava. First, the two methods were applied to the gait of a healthy subject, and experimentally validated by means of a portable gas analyzer in several 5-min tests. Then, both methods were used for a SO subject during crutch-assisted gait wearing either a passive or an active knee-ankle foot orthosis (KAFO), in order to compare the energetic efficiency of both gait-assistive devices. Improved gait pattern and reduced energy consumption were the results of using the actuated gait device. Computer modeling and analysis can provide valuable indicators, as energy consumption, to assess the impact of assistive devices in patients without the need for long and uncomfortable experimental tests.Ministerio de Economía y Competitividad; DPI2015-65959-C3-1-RXunta de Galicia; ED431B2016/03

Comparison of methods to determinate ground reactions during the double support phase of gait

Postprint (published version

A Fair and EMG‑Validated Comparison of Recruitment Criteria, Musculotendon Models and Muscle Coordination Strategies, for the Inverse‑Dynamics Based Optimization of Muscle Forces During Gait

[Abstract] Experimental studies and EMG collections suggest that a specific strategy of muscle coordination is chosen by the central nervous system to perform a given motor task. A popular mathematical approach for solving the muscle recruitment problem is optimization. Optimization-based methods minimize or maximize some criterion (objective function or cost function) which reflects the mechanism used by the central nervous system to recruit muscles for the movement considered. The proper cost function is not known a priori, so the adequacy of the chosen function must be validated according to the obtained results. In addition of the many criteria proposed, several physiological representations of the musculotendon actuator dynamics (that prescribe constraints for the forces) along with different musculoskeletal models can be found in the literature, which hinders the selection of the best neuromusculotendon model for each application. Seeking to provide a fair base for comparison, this study measures the efficiency and accuracy of: (i) four different criteria within the static optimization approach (where the physiological character of the muscle, which affects the constraints of the forces, is not considered); (ii) three physiological representations of the musculotendon actuator dynamics: activation dynamics with elastic tendon, simplified activation dynamics with rigid tendon and rigid tendon without activation dynamics; (iii) a synergy-based method; all of them within the framework of inverse-dynamics based optimization. Motion/force/EMG gait analyses were performed on ten healthy subjects. A musculoskeletal model of the right leg actuated by 43 Hill-type muscles was scaled to each subject and used to calculate joint moments, musculotendon kinematics and moment arms. Muscle activations were then estimated using the different approaches, and these estimates were compared with EMG measurements. Although no significant differences were obtained with all the methods at statistical level, it must be pointed out that a higher complexity of the method does not guarantee better results, as the best correlations with experimental values were obtained with two simplified approaches: the static optimization and the physiological approach with simplified activation dynamics and rigid tendon, both using the sum of the squares of muscle forces as objective function.This work was funded by the Spanish MICIU under project PGC2018-095145-B-I00, co-financed by the EU through the EFRD program, and by the Galician Government under grant ED431C2019/29. Moreover, F. Michaud would like to acknowledge the support of the Spanish MINECO by means of the doctoral research contract BES-2016–076901, co-financed by the EU through the ESF programXunta de Galicia; ED431C2019/2

Estimation of muscular forces from SSA smoothed sEMG signals calibrated by inverse dynamics-based physiological static optimization

The estimation of muscular forces is useful in several areas such as biomedical or rehabilitation engineering. As muscular forces cannot be measured in vivo non-invasively they must be estimated by using indirect measurements such as surface electromyography (sEMG) signals or by means of inverse dynamic (ID) analyses. This paper proposes an approach to estimate muscular forces based on both of them. The main idea is to tune a gain matrix so as to compute muscular forces from sEMG signals. To do so, a curve fitting process based on least-squares is carried out. The input is the sEMG signal filtered using singular spectrum analysis technique. The output corresponds to the muscular force estimated by the ID analysis of the recorded task, a dumbbell weightlifting. Once the model parameters are tuned, it is possible to obtain an estimation of muscular forces based on sEMG signal. This procedure might be used to predict muscular forces in vivo outside the space limitations of the gait analysis laboratory.Postprint (published version

Lower Back Injury Prevention and Sensitization of Hip Hinge with Neutral Spine Using Wearable Sensors during Lifting Exercises

[Abstract] The popularization and industrialization of fitness over the past decade, with the rise of big box gyms and group classes, has reduced the quality of the basic formation and assessment of practitioners, which has increased the risk of injury. For most lifting exercises, a universal recommendation is maintaining a neutral spine position. Otherwise, there is a risk of muscle injury or, even worse, of a herniated disc. Maintaining the spine in a neutral position during lifting exercises is difficult, as it requires good core stability, a good hip hinge and, above all, observation of the posture in order to keep it correct. For this reason, in this work the authors propose the prevention of lumbar injuries with two inertial measurement units. The relative rotation between two sensors was measured for 39 voluntary subjects during the performance of two lifting exercises: the American kettlebell swing and the deadlift. The accuracy of the measurements was evaluated, especially in the presence of metals and for fast movements, by comparing the obtained results with those from an optical motion capture system. Finally, in order to develop a tool for improving sport performance and preventing injury, the authors analyzed the recorded motions, seeking to identify the most relevant parameters for good and safe lifting execution.This work was funded by the Spanish MCI under project number PGC2018-095145-B-I00, co-financed by the EU through the EFRD program, and by the Galician Government under grant numbers ED431C2019/29 and IN853B-2018/02.Xunta de Galicia; ED431C 2019/29Xunta de Galicia; IN853B-2018/0

Skeletal-level control-based forward dynamic analysis of acquired healthy and assisted gait motion

This is a pre-print of an article published in Multibody System Dynamics. The final authenticated version is available online at: https://doi.org/10.1007/s11044-018-09634-4[Abstract] Gait analysis is commonly addressed through inverse dynamics. However, forward dynamics can be advantageous when descending to muscular level, as it allows that activation and contraction equations are integrated with motion thus providing better dynamic consistency, or when studying assisted gait, as it enables the estimation of the interaction forces between subject and devices. Control-based methods seem to be the most natural choice to carry out the forward-dynamics analysis of an acquired gait, but several options exist in their application. The paper explores such options for healthy and assisted gait, and concludes that the computed torque control of all the subject's degrees of freedom is the most reliable alternative. Moreover, the study of its more problematic underactuated variant accompanied by contact models showed to be connected to neighbor challenging topics as gait prediction or walking simulation of humanoids.Ministerio de Economía y Competitividad; DPI2015-65959-C3-1-

Using Accelerometer Data to Tune the Parameters of an Extended Kalman Filter for Optical Motion Capture: Preliminary Application to Gait Analysis

[Abstract] Optical motion capture is currently the most popular method for acquiring motion data in biomechanical applications. However, it presents a number of problems that make the process difficult and inefficient, such as marker occlusions and unwanted reflections. In addition, the obtained trajectories must be numerically differentiated twice in time in order to get the accelerations. Since the trajectories are normally noisy, they need to be filtered first, and the selection of the optimal amount of filtering is not trivial. In this work, an extended Kalman filter (EKF) that manages marker occlusions and undesired reflections in a robust way is presented. A preliminary test with inertial measurement units (IMUs) is carried out to determine their local reference frames. Then, the gait analysis of a healthy subject is performed using optical markers and IMUs simultaneously. The filtering parameters used in the optical motion capture process are tuned in order to achieve good correlation between the obtained accelerations and those measured by the IMUs. The results show that the EKF provides a robust and efficient method for optical system-based motion analysis, and that the availability of accelerations measured by inertial sensors can be very helpful for the adjustment of the filters.This work was funded by the Spanish MCI under project PGC2018-095145-B-I00, co-financed by the EU through the EFRD program, and by the Galician Government under grant ED431C2019/29. Moreover, F. Michaud would like to acknowledge the support of the Spanish MCI by means of the doctoral research contract BES-2016-076901, co-financed by the EU through the ESF programXunta de Galicia; ED431C2019/2