HBM development
Gait analysis is a major application of musculoskeletal modeling and one that holds a large potential for clinical applications of HBM. The idea behind the muscle model real time force and torque display is that movements recorded in a gait laboratory by motion capture technology can be imposed directly on the model together with measured ground reaction forces. With the movement and external forces known, the result can display internal forces in the body and for the first time present to medical staff and patient the array of forces in the body as they occur, something that is not possible at this moment in time.
Forces are invisible to the eye. HBM changes that and allows forces to become visible to the eye through color space changes in the muscle model representing the patient immersed in the system. Much like an X-ray system can show the bones in the body, HBM will be able to show the transference of forces in the body as they occur.
Muscle forces become visible in real time.
Forces are invisible by nature, we can normally only see the results of applied forces on the surrounding world. HBM makes it possible to view the generated muscle forces in the human body in real-time, in a way that makes clear the force transference in the human musculoskeletal system. The process of achieving this new functionality relies on fast and accurate real time motion capture data processing into an IK (inverse kinematics) skeletal layer containing joint positions and orientations, a further process deriving accelerations and velocities, a further process deriving forward and inverse dynamics in real time, and a final process converting the result streams into 3D visualizations of color and form changes in a 3D accurate human body muscle model. The simple act of standing is actually a complex array of motions combined muscular and neurological biofeedback mechanisms in the human body. Muscle forces are exerted to maintain balance and corrections are applied continuously.
Computational pipeline.
The computational pipeline that results in real time muscle force display is flexible and allows forward dynamics simulations to be run at any time during runtime of the system. The flow of movements as an input to the inverse dynamics simulation is stopped during a sequence and the calculated joint movements are now used as input, while the movements become output. Thus forward simulations calculate movements and reaction forces from moments of force produced around the joints of the subjects.
Flowchart
Input from the motion capture in the form of 3D marker coordinates is used as input for the Kinematics Solver. The Kinematics solver is also using resource files of a skeleton definition and marker set templates. The Kinematics Solver is outputting in real-time the current skeleton pose, the deltas of velocities and deltas of acceleration that are used as input to the Motion Equations. The Kinematics Solver also sends out Muscle paths for all respective muscles, and outputs the schematic skeleton used for the visualization. The Motion Equations are also using input from ground reaction forces and other external forces coming from an array of Force sensors. The Motion Equations also use an input from resource files that contain the respective body mass properties. The Equations of Motion output Joint moments to the Optimization process, The Optimization process also uses input of muscle lengths and moment arms coming from the respective muscle paths. The Optimization process outputs Muscle forces used in the Real Time muscle force visualization.
Applications
HBM can be applied in Diagnostics, Rehabilitation, Fundamental and applied research, sports, ergonomics and various other fields. Some of the applications are:
Diagnostics
Rehabilitation
Slide set MMVR 16
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Ton Van Den Bogert HBM presentation at Walter Reed June 2008
The slide set for download is here in PDF format:
HBM presentation 3DMA 2008 wins the conference award
