Browsing by Author "Günther, Michael"

Now showing 1 - 13 of 13

Open Access
Comparative sensitivity analysis of muscle activation dynamics
(2015) Rockenfeller, Robert; Günther, Michael; Schmitt, Syn; Götz, Thomas
We mathematically compared two models of mammalian striated muscle activation dynamics proposed by Hatze and Zajac. Both models are representative for a broad variety of biomechanical models formulated as ordinary differential equations (ODEs). These models incorporate parameters that directly represent known physiological properties. Other parameters have been introduced to reproduce empirical observations. We used sensitivity analysis to investigate the influence of model parameters on the ODE solutions. In addition, we expanded an existing approach to treating initial conditions as parameters and to calculating second- order sensitivities. Furthermore, we used a global sensitivity analysis approach to include finite ranges of parameter values. Hence, a theoretician striving for model reduction could use the method for identifying particularly low sensitivities to detect superfluous parameters. An experimenter could use it for identifying particularly high sensitivities to improve parameter estimation. Hatze’s nonlinear model incorporates some parameters to which activation dynamics is clearly more sensitive than to any parameter in Zajac’s linear model. Other than Zajac’s model, Hatze’s model can, however, reproduce measured shifts in optimal muscle length with varied muscle activity. Accordingly we extracted a specific parameter set for Hatze’s model that combines best with a particular muscle force-length relation.
Open Access
Cross-bridge mechanics estimated from skeletal muscles’ work-loop responses to impacts in legged locomotion
(2021) Christensen, Kasper B.; Günther, Michael; Schmitt, Syn; Siebert, Tobias
Legged locomotion has evolved as the most common form of terrestrial locomotion. When the leg makes contact with a solid surface, muscles absorb some of the shock-wave accelerations (impacts) that propagate through the body. We built a custom-made frame to which we fixated a rat (Rattus norvegicus, Wistar) muscle (m. gastrocnemius medialis and lateralis: GAS) for emulating an impact. We found that the fibre material of the muscle dissipates between 3.5 and 23μJ ranging from fresh, fully active to passive muscle material, respectively. Accordingly, the corresponding dissipated energy in a half-sarcomere ranges between 10.4 and 68zJ, respectively. At maximum activity, a single cross-bridge would, thus, dissipate 0.6% of the mechanical work available per ATP split per impact, and up to 16% energy in common, submaximal, activities. We also found the cross-bridge stiffness as low as 2.2pNnm-1, which can be explained by the Coulomb-actuating cross-bridge part dominating the sarcomere stiffness. Results of the study provide a deeper understanding of contractile dynamics during early ground contact in bouncy gait.
Open Access
A geometry- and muscle-based control architecture for synthesising biological movement
(2021) Walter, Johannes R.; Günther, Michael; Häufle, Daniel F. B.; Schmitt, Syn
A key problem for biological motor control is to establish a link between an idea of a movement and the generation of a set of muscle-stimulating signals that lead to the movement execution. The number of signals to generate is thereby larger than the body’s mechanical degrees of freedom in which the idea of the movement may be easily expressed, as the movement is actually executed in this space. A mathematical formulation that provides a solving link is presented in this paper in the form of a layered, hierarchical control architecture. It is meant to synthesise a wide range of complex three-dimensional muscle-driven movements. The control architecture consists of a ‘conceptional layer’, where the movement is planned, a ‘structural layer’, where the muscles are stimulated, and between both an additional ‘transformational layer’, where the muscle-joint redundancy is resolved. We demonstrate the operativeness by simulating human stance and squatting in a three-dimensional digital human model (DHM). The DHM considers 20 angular DoFs and 36 Hill-type muscle-tendon units (MTUs) and is exposed to gravity, while its feet contact the ground via reversible stick-slip interactions. The control architecture continuously stimulates all MTUs (‘structural layer’) based on a high-level, torque-based task formulation within its ‘conceptional layer’. Desired states of joint angles (postural plan) are fed to two mid-level joint controllers in the ‘transformational layer’. The ‘transformational layer’ communicates with the biophysical structures in the ‘structural layer’ by providing direct MTU stimulation contributions and further input signals for low-level MTU controllers. Thereby, the redundancy of the MTU stimulations with respect to the joint angles is resolved, i.e. a link between plan and execution is established, by exploiting some properties of the biophysical structures modelled. The resulting joint torques generated by the MTUs via their moment arms are fed back to the conceptional layer, closing the high-level control loop. Within our mathematical formulations of the Jacobian matrix-based layer transformations, we identify the crucial information for the redundancy solution to be the muscle moment arms, the stiffness relations of muscle and tendon tissue within the muscle model, and the length-stimulation relation of the muscle activation dynamics. The present control architecture allows the straightforward feeding of conceptional movement task formulations to MTUs. With this approach, the problem of movement planning is eased, as solely the mechanical system has to be considered in the conceptional plan.
Open Access
Giraffes and hominins: reductionist model predictions of compressive loads at the spine base for erect exponents of the animal kingdom
(2021) Günther, Michael; Mörl, Falk
In humans, compressive stress on intervertebral discs is commonly deployed as a measurand for assessing the loads that act within the spine. Examining this physical quantity is crucially beneficial: the intradiscal pressure can be directly measured in vivo in humans, and is immediately related to compressive stress. Hence, measured intradiscal pressure data are utterly useful for validating such biomechanical animal models that have the spine incorporated, and can, thus, compute compressive stress values. Here, we utilise human intradiscal pressure data to verify the predictions of a reductionist spine model, which has in fact only one joint degree of freedom. We calculate the pulling force of one lumped anatomical structure that acts past this (intervertebral) joint at the base of the spine - lumbar in hominins, cervical in giraffes - to compensate the torque that is induced by the weight of all masses located cranially to the base. Given morphometric estimates of the human and australopith trunks, respectively, and the giraffe's neck, as well as the respective structures' lever arms and disc areas, we predict, for all three species, the compressive stress on the intervertebral disc at the spine base, while systematically varying the angular orientation of the species' spinal columns with respect to gravity. The comparison between these species demonstrates that hominin everyday compressive disc stresses are lower than such in big quadrupedal animals. Within each species, erecting the spine from being bent forward by, for example, thirty degrees to fully upright posture reduces the compressive disc stress roughly to a third. We conclude that erecting the spine immediately allows to carry extra loads of the order of body weight, and yet the compressive disc stress is lower than in a moderately forward-bent posture with none extra load.
Open Access
Interactive control of biomechanical animation
(1993) Ertl, Thomas; Ruder, Hanns; Allrutz, Ralf; Gruber, Karin; Günther, Michael; Hospach, Frank; Ruder, Margret; Subke, Jörg; Widmayer, Karin
Physics-based animation can be generated by performing a complete dynamical simulation of multibody systems. This leads to the solving of a complex system of differential equations in which biomechanical results for the physics of impacts are incorporated. Motion control is achieved by interactively modifying the internal torques. Realtime response requires the distribution of the workload of the computation between a high-speed compute server and the graphics workstation by means of a remote-procedure call mechanism.
Open Access
Interactive control of biomechanical animation : contribution to the GI Workshop: Visualisierung - Rolle von Interaktivitat und Echtzeit, GMD, Sankt Augustin, 2.-3. Juni 1992
(1992) Ertl, Thomas; Ruder, Hanns; Gruber, Karin; Günther, Michael; Hospach, Frank; Krebs, Thomas; Subke, Jörg; Widmayer, Karin
Physical based animation can be generated by performing a complete dynamical simulation of multi-body systems. This leads to a complex system of differential equations which has to be solved incorporating biomechanical results for the physics of impacts. Motion control is achieved by interactively modifying the internal torques. Realtime response requires the distribution of the workload of the computation between a highspeed computerserver and the graphics workstation by means of a remote procedure call mechanism.
Open Access
Is the harm-to-benefit ratio a key criterion in vaccine approval?
(2022) Mörl, Falk; Günther, Michael; Rockenfeller, Robert
Open Access
Kinematics and dynamics for computer animation
(1994) Ruder, Hanns; Ertl, Thomas; Gruber, Karin; Günther, Michael; Hospach, Frank; Ruder, Margret; Subke, Jörg; Widmayer, Karin
This tutorial will focus on the physical principles of kinematics and dynamics. After explaining the basic equations for point masses and rigid bodies a new approach for the dynamic simulation of multi-linked models with wobbling mass is presented, which has led to new insight in the field of biomechanics, but which has not been used in computer animation so far.
Open Access
Kinematics and dynamics for computer animation
(1991) Ruder, Hanns; Ertl, Thomas; Gruber, Karin; Günther, Michael; Hospach, Frank; Subke, Jörg; Widmayer, Karin
This tutorial will focus on the physical principles of kinematics and dynamics. After explaining the basic equations for point masses and rigid bodies a new approach for the dynamic simulation of multi-linked models with wobbling mass is presented, which has led to new insight in the field of biomechanics, but which has not been used in computer animation so far.
Open Access
Muscle wobbling mass dynamics : eigenfrequency dependencies on activity, impact strength, and ground material
(2023) Christensen, Kasper B.; Günther, Michael; Schmitt, Syn; Siebert, Tobias
In legged locomotion, muscles undergo damped oscillations in response to the leg contacting the ground (an impact). How muscle oscillates varies depending on the impact situation. We used a custom-made frame in which we clamped an isolated rat muscle ( M. gastrocnemius medialis and lateralis : GAS) and dropped it from three different heights and onto two different ground materials. In fully activated GAS, the dominant eigenfrequencies were 163 Hz, 265 Hz, and 399 Hz, which were signficantly higher (p < 0.05) compared to the dominant eigenfrequencies in passive GAS: 139 Hz, 215 Hz, and 286 Hz. In general, neither changing the falling height nor ground material led to any significant eigenfrequency changes in active nor passive GAS, respectively. To trace the eigenfrequency values back to GAS stiffness values, we developed a 3DoF model. The model-predicted GAS muscle eigenfrequencies matched well with the experimental values and deviated by - 3.8%, 9.0%, and 4.3% from the passive GAS eigenfrequencies and by - 1.8%, 13.3%, and - 1.5% from the active GAS eigenfrequencies. Differences between the frequencies found for active and passive muscle impact situations are dominantly due to the attachment of myosin heads to actin.
Open Access
On laterally perturbed human stance: experiment, model, and control
(2018) Suissa, Dan; Günther, Michael; Shapiro, Amir; Melzer, Itshak; Schmitt, Syn
Open Access
Theoretical hill-type muscle and stability : numerical model and application
(2013) Schmitt, Syn; Günther, Michael; Rupp, Tille; Bayer, Alexandra; Häufle, Daniel F. B.
The construction of artificial muscles is one of the most challenging developments in today's biomedical science. The application of artificial muscles is focused both on the construction of orthotics and prosthetics for rehabilitation and prevention purposes and on building humanoid walking machines for robotics research. Research in biomechanics tries to explain the functioning and design of real biological muscles and therefore lays the fundament for the development of functional artificial muscles. Recently, the hyperbolic Hill-type force-velocity relation was derived from simple mechanical components. In this contribution, this theoretical yet biomechanical model is transferred to a numerical model and applied for presenting a proof-of-concept of a functional artificial muscle. Additionally, this validated theoretical model is used to determine force-velocity relations of different animal species that are based on the literature data from biological experiments. Moreover, it is shown that an antagonistic muscle actuator can help in stabilising a single inverted pendulum model in favour of a control approach using a linear torque generator.
Open Access
Where have the dead gone?
(2022) Günther, Michael; Mörl, Falk; Rockenfeller, Robert