Abstract

In this post-graduate dissertation (Habilitation), entitled “Virtual Biomechanics and its Physics,” the thematic of a simulation system for biomechanics is discussed. The topic centers on the system as it is realized through the author’s developments. The prerequisites of a simulation system, the physical laws that form a necessary subset, are selected. For this selection process the physical laws were carefully examined. The result of this process is visible in the first part of this work. The list of physical laws is not the simple result of the selection process, but rather it is the outcome of a rigorous process of seeking to understand them and find their usefulness and their necessity as the basis for a simulation system. Newton’s mechanics is still the basis of today’s technology, together with what we know about signals and information. This is also true for the physics that drives a simulation system. Deterministic chaos is beginning to play a role in biological systems and hence in simulation systems as well. Quantum mechanics and quantum field theory do not play a prominent part in simulation systems. However, they are important in explaining mass; the function of muscles on the macroscopic scale and the functioning of the brain (see Chapter 9 – discussion), but no tangible explanations are available. How can the human body be represented in mathematical terms? The frequently used rigid body models and their physics are described in detail. Extensions of this concept are reviewed in the discussion section. The project creation depicts the author’s specific solution. Segment vectors are defined, and herewith “calibration” is explained. “Calibration” here is the specific process that allows calculating joint coordinates from marker coordinates, which was developed by the author. Further, filtering is discussed, which without inverse dynamics would be impossible. Within the topic, F³ filtering is detailed, which is the author’s development and which allows removing most unwanted frequencies with no shifting and no endpoint problems. The data conversion (from Cartesian joint coordinates to Cardan angles) and the actual model design conclude the project creation. The approximation of muscle energies is of major interest. Starting with rigid body models, the joints, respectively the surrounding muscles are identified as energy sources. This approach works without considering the detailed muscle anatomy, because for a given movement energy must be delivered regardless of the specific muscle arrangement. The amount of energy can be calculated from the angular joint moments and the respective angular velocities. The energy transfer between adjacent joints is also considered. External forces acting on a body have great influence on its movement and its dynamical parameters like energy, momentum, etc. If all force vectors and their points of application are measured, the system is well determined. In most studies, however, the forces are hard to determine and might even be impossible to measure. Force exchange models help us to approximate the unknown forces and their points of application. These models were developed by the author for the entire spectrum of ground reaction forces, from standing to walking, running and jumping. The author’s working simulation system is presented in detail. It consists of the Human-Builder component, which was exclusively developed by the author, and the SD 6.2 Solid Dynamics simulator. Human-Builder is a system that prepares simulation projects for use with SD 6.2. A mathematical body model, with the individual’s anthropometric measurements, is set up. Together with filtered, converted, and calibrated data, this forms the basis of a simulation which after compilation runs in SD 6.2 without further programming. Four selected studies which were carried out by the author demonstrate the usefulness and workability of the system. Study one is concerned with energy expenditure in running. It is shown that results derived from inverse dynamics are in agreement with results from studies using the oxygen intake method. It is further shown that additional data can be obtained. While the oxygen intake method can be used for aerobic movement only, the simulation method can produce results for anaerobic movements as well. Further, the energy expenditure of specific joints can be stated, while oxygen intake only gives data for the entire body. The efficiency of martial arts kicks is inspected in the second example. Energy expenditure, together with kicking velocity and the subjects’ anthropometry, are the basis of the definition of efficiency. It was found that flexibility and experience are the major ingredients of effective kicks. The efficiency of judo throws, example three, was also examined by means of simulation. It was found that momentum transfer is of major importance for a successful throw. The simulation allows inspecting the entire movement and enables us to record those movement sequences that need to be altered for a successful performance. In weightlifting, example four, energy consumption seems to be a very sensitive parameter with regard to correct or incorrect movement. Also here the different phases of a movement can be inspected and correlated with different trials of the same or other athletes. Verf.-Referat