Background: Running with the appropriate intensity may produce a positive influence on the mechanical properties of cortical bone structure. However, few studies have discussed the effects of different running intensities on the mechanical properties at different levels, especially at the micro-level, because the micromechanical parameters are difficult to measure experimentally. Methods: An approach that combines finite element analysis and experimental data was proposed to predict a micromechanical parameter in the rat femoral cortical bone structure, namely, the micro-level failure strain. Based on the previous three-point bending experimental information, fracture simulations were performed on the femur finite element models to predict their failure process under the same bending load, and the micro-level failure strains in tension and compression of these models were back-calculated by fitting the experimental load–displacement curves. Then, the effects of different running intensities on the micro-level failure strain of rat femoral cortical bone structure were investigated. Results: The micro-level failure strains of the cortical bone structures expressed statistical variations under different running intensities, which indicated that different mechanical stimuli of running had significant influences on the micromechanical properties. The greatest failure strain occurred in the cortical bone structure under low-intensity running, and the lowest failure strain occurred in the structure under high-intensity running. Conclusions: Moderate and low-intensity running were effective in enhancing the micromechanical properties, whereas high-intensity running led to the weakening of the micromechanical properties of cortical bone. Based on these, the changing trends in the micromechanical properties were exhibited, and the effects of different running intensities on the fracture performance of rat cortical bone structures could be discussed in combination with the known mechanical parameters at the macro- and nano-levels, which provided the theoretical basis for reducing fracture incidence through running exercise.

Three numerical methods, including element instantaneous failure, continuum damage mechanics, and extended finite element methods, are mainly used to simulate the fracture in cortical bone structure. Although many simulations focus on the cortical bone fracture, few have investigated the differences in prediction accuracy among the three numerical methods. The purpose of this study was to evaluate the prediction accuracy and applicability of the three numerical methods in simulating cortical bone fracture under bending load. The rat femur samples were first used to perform the three-point bending experiment. Then, the three numerical methods were respectively used to conduct fracture simulation on the femoral finite element models. Each result was compared with the experimental data to determine the prediction accuracy. The results showed that fracture simulation based on the continuum damage mechanics method was in better agreement with the experimental results, and observable differences in the failure processes could be seen in the same model under the three simulations due to various element failure strategies. The numerical method that was suitable for simulating cortical bone fracture under bending load was determined; meanwhile, the variations in the failure simulations were observed, and the cause of the variations in the predicted results using different numerical methods was also discussed, which may have potential to improve the prediction accuracy of cortical bone fracture.