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13:30   Neuromechanics I Chair: Winfred Mugge 13:30 15 mins MUSCULOSKELETAL MODEL OF HAND AND WRIST IN OPENSIM Mojtaba Mirakhorlo, Huub Maas, Dirkjan Veeger, Ilse Jonkers Abstract: A musculoskeletal model of the hand and wrist may be of value to provide more insight into the mechanics and neural control of finger movements. The aim of this study was to build a musculoskeletal model of the hand and wrist composing all muscles, the carpo-radial, metacarpal and phalangeal joints. We built a 3D dynamic model comprising the segments of hand and wrist as well as the muscles of forearm and hand. In total the model comprises of 19 segments (the carpal bones were modeled as one segment) with 23 degrees of freedom and 45 muscles. All required anatomical input data, such as bone masses and inertias, joint axis positions and orientations and muscle morphological parameters (including PCSA, mass, optimal fiber length and tendon length as well as muscle origins, insertions and via-points) were obtained from a cadaver of which the data set was recently published [1]. As a first step, model validity was investigated by comparing model kinematic outputs (moment arms) for the index and middle finger’s extrinsic and intrinsic muscles with experimental measurements [2]. We computed the moment arms of extrinsic muscles (flexor digitorum profundus, flexor digitorum superficialis and extensor digitorum communis) and intrinsic muscles (dorsal or radial interosseous, lumbricals, palmar or ulnar interosseous ) for both the index and middle finger. Moment arms were computed during flexion of the metacarpophalangeal, proximal and distal interphalangeal joints. Good agreement between experimentally measured and computed moment arms was found, particularly for extrinsic muscles. The magnitudes of moment arms of the intrinsic muscles differed more, but their patterns were comparable. In future research, we will validate the model kinetically. When validated and reliable, the model provides a tool for the investigation of hand (dys)function. More specific, the role of (inter)connections between tendons and muscles in motor control of hand motion will be assessed. REFERENCES [1] M. Mirakhorlo, J. M. Visser, B. Goislard de Monsabert, F. van der Helm, H. Maas, and H. Veeger, "Anatomical parameters for musculoskeletal modeling of the hand and wrist," International Biomechanics, vol. 3, pp. 40-49, 2016. [2] K.-N. An, Y. Ueba, E. Chao, W. Cooney, and R. Linscheid, "Tendon excursion and moment arm of index finger muscles," Journal of biomechanics, vol. 16, pp. 419-425, 1983. 13:45 15 mins DEVELOPMENT OF A METHOD TO DETERMINE ABNORMAL JOINT TORQUE COUPLING PATTERNS DURING WALKING IN CHRONIC HEMIPARETIC STROKE Simone Fricke, Andrew Dragunas, Keith Gordon, Herman van der Kooij, Edwin van Asseldonk, Julius Dewald Abstract: Abnormal joint torque coupling between (sub)maximal isometric hip extension and hip adduction torques was found in individuals with chronic hemiparetic stroke in a previous study [1], however, it is unclear how this coupling affects dynamic tasks like walking. Especially during stance phase of gait, in which hip extension and abduction torques need to be generated simultaneously, this abnormal hip extension/adduction coupling might lead to instability. Therefore, the aim of this study was to develop a method to quantify joint torque coupling patterns in stroke patients by modulating hip extension torques during walking. We developed a method to increase or decrease hip extension torques during walking in the sagittal plane and measure the effect on hip abduction/adduction torques. A motor which was placed behind a treadmill was attached to the pelvis of the subject and a constant force was applied in anteroposterior direction while the subject was walking. Each subject participated in three to five trials of two minutes and in each trial a different force was applied in either forward or backward direction. For each trial, joint angles and joint torques were calculated based on kinematic data and ground reaction forces. Preliminary results of one healthy participant and one stroke patient indicate that hip extension torques during stance phase of walking could be modulated by applying forces in anteroposterior direction to the pelvis. In addition to this, changes of hip abduction torques during stance phase were found. For example, applying a force in backward direction led to a larger hip extension torque and less hip abduction torque compared to normal walking in both participants. In contrast to this, applying a force in forward direction resulted in less hip extension torque and larger hip abduction torque. Based on these preliminary findings, we conclude that applying a force in anteroposterior direction to the pelvis during walking might be used to modulate hip extension torques and measure joint torque coupling in the abduction/adduction degree of freedom during walking. After further optimizing our protocol, additional experiments will be performed in individuals with stroke and healthy participants. Results of these future experiments are expected to provide insight into the effect of abnormal joint torque coupling patterns on walking stability following stroke and may lead to the development of new more subject specific therapies. 14:00 15 mins MEASUREMENT OF KNEE JOINT KINEMATICS USING A 3D-TRACKED A-MODE ULTRASOUND SYSTEM Kenan Niu, Victor Sluiter, Jasper Homminga, André Sprengers, Nico Verdonschot Abstract: Introduction: Improving the accuracy of measuring knee joint kinematics is a crucial step in gait analysis. The use of skin-mounted markers is well established, in which the trajectories of skin markers represent the movements of the bony segments beneath the skin. However, the skin-marker estimated kinematics is subject to soft tissue artefacts (STA), with errors ranging from 2 mm to a maximum of 50 mm [1]. Alternatively, fluoroscopic systems have been reported to achieve accuracies of kinematics in the order of 1 mm and 2 degrees [2], but induced irradiation to the subject and a limited field of view hampers routine usage on large patient cohorts. The aim of this study is to assess the feasibility of measuring knee joint kinematics using a 3D-tracked A-mode ultrasound system in an in-vitro experiment and calculate the achievable accuracy of joint kinematics relative to the ground truth. Methods: An intact cadaveric leg was fixated in a flexion-extension rig facilitating flexion of the leg in a quasi-static manner. Two optical tracking probes were mounted to femur and tibia separately, which provided the ground truth of knee joint movement. A 3D-tracked A-mode ultrasound probe was used to acquire 30 anatomical spots distributed homogeneously over tibia and femur, whilst covering specific anatomical landmarks on lower limb, e.g. great trochanter, femoral lateral/medial epicondyles, tibial epicondyle and ankle. The acquired point clouds were fed to a registration algorithm that combined an iterative closest point and perturbation method to register the acquired point clouds to corresponding bony segments in five different flexion angles. Results: The resulting kinematics showed an average error of 1-2° and 1-2mm for flexion/extension and adduction/abduction, and an average error of 3° and 3 mm for rotation along the internal/external axis. Conclusion: This study has presented a 3D-tracked A-mode ultrasound system and proven its feasibility of the reconstructed knee joint kinematics in an in-vitro experiment. The accuracy measured in this in-vitro experiment outperforms the error of in-vivo experiments using skin-mounted markers and is comparable to the accuracy of Fluoroscopy based systems. Thus, this A-mode Ultrasound approach could provide a low invasive method for measuring knee joint kinematics with higher accuracy. REFERENCES [1] Cappozzo A, Della Croce U, Leardini A, Chiari L, “Human movement analysis using stereophotogrammetry: Part 1: theoretical background”, Gait & posture, 21 (2):186-196, (2005). [2] Guan S, Gray HA, Keynejad F, Pandy MG, “Mobile Biplane X-Ray Imaging System for Measuring 3D Dynamic Joint Motion During Overground Gait”, IEEE transactions on medical imaging, 35 (1):326-336, (2016) 14:15 15 mins AMBULATORY HAND FORCE ESTIMATION DURING MANUAL LIFTING USING AN INERTIAL SENSOR SUIT AND INSTRUMENTED FORCE SHOES Gert Faber, Idsart Kingma, Max Chang, Jack Dennerlein, Jaap van Dieën Abstract: Background: Hand forces (HFs) are often measured during biomechanical assessment of manual materials handling. In most field studies it is not possible to directly measure HFs without affecting the natural motion pattern. Therefore, in a previous study we proposed a HF estimation method based on ground reaction forces (GRFs) and body segment accelerations [1]. As a proof-of-principle this method was tested with laboratory equipment: GFRs were measured with force plates (FPs) and segment acceleration were measured using an optical motion capture (OMC) system. In the current study, we evaluated the same HF estimation method but now based on an ambulatory measurement system, consisting of inertial motion capture (IMC) instead of an OMC system and instrumented force shoes (FSs) instead of FPs. Methods: Eight male and eight female participants lifted a 10-kg box from ground level while 3D full-body kinematics (segment accelerations) were measured using an OMC and an IMC system and 3D GRFs were measured using a FPs and FSs. 3D HFs were estimated three times based on different data sources: 1) FP+OMC, 2) FP+IMC and 3) FS+IMC. Based on these sources, 3D HFs were estimated by taking the GRFs and subtracting the forces due to weight and acceleration of all body segments [1]. The estimated HFs were compared (RMSerror) to reference HFs that were calculated based on box kinematics and the GRFs of a FP that the box was lifted from. Results: Averaged over subjects and 3D force directions, the HF RMSerror was 8N when using the laboratory equipment (FP+OMC). When using the IMC instead of OMC data (FP+IMC), RMSerror increased to 11N. Finally, when replacing the FP data with the FS (FS+IMC), RMSerror increased to 14N. Discussion: The ambulatory measurement system was able to estimate hand forces with a inaccuracy of about 15N (15% of box weight). Whether this error is acceptable depends on the application of the method and the concomitant accuracy requirements. For example, for the assessment of low back loading during manual lifting, this error seems acceptable. Assuming a moment arm of 0.5m from the low back to the hands this error would result in about 7.5Nm error in low-back moment estimates, which is small relative to peak low-back moments of 200-300 Nm during manual lifting . 14:30 15 mins 3D ULTRASOUND ASSESSMENT OF MUSCLE MORPHOLOGY; A COST EFFECTIVE APPROACH Guido Weide, Stephan van der Zwaard, Peter Huijing, Richard Jaspers, Jaap Harlaar Abstract: ABSTRACT In (pre-)clinical practice, healthcare and sports imaging and morphometry of muscles is indispensable in diagnostics and/or follow-up evaluations after treatment or training. Magnetic resonance imaging (MRI) offers an approach to assess the morphometry of muscles, however this technique is highly expensive, time-consuming and restricts control over the subjects posture and movement due to limited space in the MRI. Freehand 3D ultrasound offers an alternative to MRI, which is easy to apply and cost effective1,2. Applying 3DUS and reconstructing a voxel array, 6 basic steps need to be taken: 1) locate the US transducer using a Motion Capture system, 2) calibrate the location and orientation of ultrasound images relative to the transducer, 3) capture a sequence of B-mode ultrasound images using freehand scanning, 4) temporally synchronize the Motion Capture system and US video stream, and 5) fill a voxel array by placing the sequentially captured and located US images, 6) segmentation of the voxel array into known anatomical structures using conventional software tools. Here we demonstrate this calibrated 3DUS approach for volume and fascicle length determination of m. vastus lateralis and m. gastrocnemius medialis and show its validity and reliability on cadavers. 3DUS scans were collected using four male human cadavers, age at death 76.8±7.9 years. Fascicle length and volume were measured three times and proved to have an excellent intra-rater reliability (ICC3,3 of 0.983 [0.944-0.996] and 0.998 [0.995-1] respectively). Using a Pearsons correlation criterion, criterion validity was assessed for fascicle length and volume. Both fascicle length and volume measured with 3D ultrasound correlated significantly with the criterion values (r= 0.998 and r=0.985 respectively). 3DUS imaging provides a fast approach for morphometric measurements of skeletal muscles. In this study we have shown that volume and fascicle length determination of the m. vastus lateralis and the m. gastrocnemius medialis with 3DUS is accurate. Besides examination of typical skeletal muscles, 3DUS can also proof to be useful in an up to now conventionally performed US examination (i.e. in 2D) in e.g. neurological disorders, muscle disease critical illness, cardiovascular as well as effects of physical training. REFERENCES 1. Prager RW, Rohling RN, Gee AH, Berman L. Rapid calibration for 3-D freehand ultrasound. Ultrasound Med Biol. 1998;24(6):855-869. 2. Weide G, Huijing PA, Maas JC, Becher JG, Harlaar J, Jaspers RT. Medial gastrocnemius muscle growth during adolescence is mediated by increased fascicle diameter rather than by longitudinal fascicle growth. J Anat. 2015;226(6):530-541. 14:45 15 mins JOINT-LEVEL RESPONSES TO COUNTERACT PERTURBATIONS DURING HUMAN WALKING Mark Vlutters, Edwin van Asseldonk, Herman van der Kooij Abstract: Most current lower extremity exoskeletons are unable to stay upright without assistance and guidance of its user. Paraplegic users, for example, often require crutches to prevent falling. To have an exoskeleton assist its user in maintaining balance instead, preferably in a natural and human-like manner, an understanding of human balance control is of major importance. Investigating balance responses following perturbations can give insight in the human balance controller. When and how are the different lower extremity joints controlled to maintain upright posture? Furthermore, insight into joint angles, torques, and power during perturbation recovery can provide guidelines for exoskeleton hardware specifications. In this study, pelvis perturbations were used to elicit balance recovery responses in walking human subjects. We investigated how joint-level responses alter with perturbation magnitude and direction, and provide insight in the ranges of motion, torque, and power of the ankle, knee, and hip joints during the recovery. Ten healthy young adults walked on a dual-belt instrumented treadmill, and randomly received transient mediolateral and anteroposterior pelvis perturbations of various magnitudes at the instance of toe-off right. Kinematic and ground reaction force data were collected to capture the subjects’ balance responses. Data were processed using Matlab (R2014, Mathworks, US) and OpenSim 3.3, an open source multibody dynamics software package [1]. Joint angles and velocities were calculated using inverse kinematics, joint torques using inverse dynamics, and joint power by multiplying the joint velocities and torques. The ankle torques and power show that an ankle strategy is actively addressed in the recovery from pelvis perturbations during walking, opposing movement in the direction of the perturbation. Furthermore, hip torques in the swing leg, used for corrective stepping, indicate that the leg is actively positioned for foot placement in both the frontal and sagittal planes. Responses in ankle, knee, and hip joints scale with perturbation magnitude, depending on the perturbation direction. The presented results give insight in human balance control on a joint level. Future work consists of finding controllers that can generate such joint-level responses. [1] S.L.Delp, et al., “OpenSim: Open-source software to create and analyse dynamic simulations of movement”, IEEE Trans. Biomed. Eng., Vol. 54, pp. 1940-1950, (2007).