15 Fakultätsübergreifend / Sonstige Einrichtung

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/16

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2013 - 20153

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Institute: search.filters.UBSInstitut.Institut für Sport- und BewegungswissenschaftPublication Type: search.filters.UBSTyp.Zeitschriftenartikel

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    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.
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    Walkability is only part of the story : walking for transportation in Stuttgart, Germany
    (2014) Reyer, Maren; Fina, Stefan; Siedentop, Stefan; Schlicht, Wolfgang
    In modern Western societies people often lead inactive and sedentary lifestyles, even though there is no doubt that physical activity and health are related. From an urban planning point of view it would be highly desirable to develop built environments in a way that supports people in leading more active and healthy lifestyles. Within this context there are several methods, predominantly used in the US, to measure the suitability of built environments for walking and cycling. Empirical studies show that people living in highly walkable areas are more physically active (for example, walk more or cycle more). The question is, however, whether these results are also valid for European cities given their different urban planning characteristics and infrastructure standards. To answer this question we used the Walkability-Index and the Walk Score to empirically investigate the associations between walkability and active transportation in the city of Stuttgart, Germany. In a sample of household survey data (n = 1.871) we found a noticeable relationship between walkability and active transportation—the more walkable an area was, the more active residents were. Although the statistical effect is small, the health impact might be of relevance. Being physically active is multi-determined and not only affected by the walkability of an area. We highlight these points with an excursion into research that the health and exercise sciences contribute to the topic. We propose to strengthen interdisciplinary research between the disciplines and to specifically collect data that captures the influence of the environment on physical activity in the future.
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    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.