The energy metabolism during concentric and eccentric muscular exercise: experiment, model and validation.

• Applicants: Dr.-Ing. Alexander Gussew; Dr. Stefan Hochstein; Privatdozent Dr. Norman Stutzig
• Subject Area: Medical Physics, Biomedical Technology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 546033411

Regular physical activity has a positive effect on the prevention and treatment of metabolic, cardiovascular, oncological and neurodegenerative diseases. For this reason, the valid determination of physical activity in everyday life is of great importance. Physical activity can be characterized by the energy expenditure of the muscles. However, previous methods for determining energy expenditure are either too imprecise or not suitable for everyday use. An alternative method is to simulate the muscular energy metabolism using musculo-skeletal models. Such models can depict the energy turnover of individual muscles well for concentric loads, but are still less sufficient for eccentric loads. The main goal of this project is to develop and validate a musculoskeletal model (in terms of a multi-body model) that can predict energy expenditure during single-joint concentric and eccentric contractions using the example of plantar flexion of the ankle joint. For this purpose, an approach combining numerical as well as experimental methods will be used. Existing Hill-type muscle models will be adapted in order to enable determination of energy consumption rates. Subsequently, these modified models will be combined in one musculo-skeletal multi-body model (consisting of lower leg, ankle, and foot), which will provide simulation of the energy expenditure during concentric and eccentric movements during plantar flexion. In parallel, measurements of the energy expenditure in the working muscles will be implemented based on functional phosphorus magnetic resonance spectroscopy (31P-fMRS) and tested in in vivo experiments with calf muscle loads performed with an MR-compatible pedal ergometer. Based on spectroscopically metabolic parameters, ATP turnover rates will be quantified and compared with the energy expenditure rates predicted by the model under different exercise regimes (different intensity and duration) and forms of movement (concentric and eccentric voluntary contractions). In addition, the load-specific electromyographic parameters, which are recorded simultaneously to the 31P-fMRS, will be used as model input variables to characterize the simulated loads. This experimental approach serves to validate the energy expenditure prediction achieved by means of the developed Hill-type muscle models as well as new multi-body model, which will be built as a part of the project. The results of the project represent the fundamental basis for more complex musculo-skeletal models targeting on determination of the energy metabolism during everyday motion.

• DFG Programme: Research Grants