An activatable molecular spring reduces muscle tearing during extreme stretching |
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| Authors: | TR Leonard V Joumaa W Herzog |
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| Institution: | 1. Biomedical Engineering, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada;2. Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada;3. Department of Cell Biology and Anatomy, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada;4. Advanced Imaging and Histopathology Core, Qatar Biomedical Research Institute, Hamad Bin Khalifa University, Qatar Foundation, Doha, Qatar;5. Biomechanics Laboratory, School of Sports, Federal University of Santa Catarina, Florianopolis, SC, Brazil |
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| Abstract: | The purpose of this study was to determine failure stresses and failure lengths of actively and passively stretched myofibrils. As expected, myofibrils failed at average sarcomere lengths (about 6–7 μm) that vastly exceeded sarcomere lengths at which actin–myosin filament overlap ceases to exist (4 μm) and thus actin–myosin-based cross-bridge forces are zero at failure. Surprisingly, however, actively stretched myofibrils had much greater failure stresses and failure energies than passively stretched myofibrils, thereby providing compelling evidence for strong force production independent of actin–myosin-based cross-bridge forces. Follow-up experiments in which titin was deleted and cross-bridge formation was inhibited at high and low calcium concentrations point to titin as the regulator of this force, independent of calcium. The results of this study point to a mechanism of force production that reduces stretch-induced muscle damage at extreme length and limits injury and force loss within physiologically relevant ranges of sarcomere and muscle lengths. |
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