Effects of different running intensities on the micro-level failure strain of rat femoral cortical bone structures: a finite element investigation

Abstract

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.

Keywords: Back-calculation; Cortical bone; Micro-level failure strain; Running intensity; Three-point bending load.

Fig. 1

Comparison of the prediction precision with different tensile failure strains

Fig. 2

The load–displacement curves obtained from the experiment and simulation in each rat group. a SED group; b EX12 group; c EX16 group; d EX20 group

Fig. 3

The failure process in the FE model under three-point bending load and the comparison of the fracture patterns between the present simulation and the previous experiment. The “SDV1” represents the damage variable D. a initial loading stage; b element damage stage; c element failure stage; d structure fracture stage; e experimental fracture pattern

Fig. 4

The schematic diagrams of the boundary condition on the rat femur under three-point bending. a the experimental boundary condition; b the simulated boundary condition

Fig. 5

Flow chart of the prediction process for the micro-level failure strain

Fig. 6

Mesh sensitivity analysis for the finite element models with different mesh size