Impact response of active muscle: experimentation and modelling

• Applicants: Professor Dr. Syn Schmitt; Professor Dr. Tobias Siebert
• Subject Area: Human Factors, Ergonomics, Human-Machine Systems ; Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
• Term: since 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 234087184

Biological locomotion is driven by skeletal muscles. Muscle masses are suspended compliantly at the skeleton. The muscles' ingenious construction tolerates impacts during their contractile function. For example, a fast run induces such impacts when legs contact the ground. As a response to these impacts, damped oscillations are superposed to the driving muscle contractions. Our aim is to better understand muscular contraction, locally within the muscle and of the muscle as a whole, in response to a variety of realistic acceleration scenarios. In both previous funding periods, we developed a setup enabling the measurement of impact-induced muscle wobbling directly on the muscle surface. Moreover, we advanced the experimental impact analysis by determining both elastic and damping properties, well down to the cross-bridge level, with the establishment of a work-loop technique. We also advanced the model branch in our research: The first-order cross-bridge model has been merged with a muscle’s mass distribution along the fibre or belly. The resulting second-order model can now be deployed to simulate the impact situations in our experiments. In addition, we were able to provide clear evidence that muscle inertia is generally a crucial factor in the evolution of terrestrial animals, as it is a particular property that limits maximum speed in legged running. In this final project phase applied for, specific open questions that arose from both previous funding periods are to be answered, to gain a better understanding of the design criteria and muscle mechanics during impacts. To expedite knowledge about muscular design, we will validate our muscle model on experimental data with varying impact scenarios (changing: impact force, impact time duration, muscle length, contractile history). In order to understand the influence of titin on the passive fibre material, it has been found necessary to improve the titin model as a further crucial structural extension to our contractile model part (the engine located in the cross-bridges). As another validation step for our second-order model, we will apply our work-loop technique to determine the local mechanical energy dissipation, in addition to simply analyse the local strain signals, during impact-induced wave propagation, thereby making use of our more localised camera views of different muscle regions.This project gains basic knowledge about the structure-function relation of skeletal muscle, and, with this, prospectively helps in gaining a causal understanding of muscle tissue maintenance and recovery in daily use, muscle damage in overload situations, muscle regeneration in patients by linking typical external loading conditions, which often come along with superposed shock-wave propagation, to internal dynamic processes within the muscle tissue. Additionally, an enhanced knowledge about the design of the universal biological actuator 'muscle' will help in the design of biomimetic robotic actuators.

• DFG Programme: Research Grants