<p>Bone microdamage, frequently induced by high-impact activities such as military training and sports, poses significant health risks when accumulated over time. However, this microdamage often eludes detection using conventional diagnostic techniques, necessitating the development of innovative, non-destructive testing methods for early diagnosis and prevention. Here, we investigated the complete fatigue fracture process of bone using terahertz time-domain spectroscopy (THz-TDS) to evaluate the effects of varying damage levels, induced by parameters such as the number of cycles and maximum stress, on spectral coefficients. Our findings demonstrate that both the refractive index and absorption coefficient are highly sensitive to the degree of bone damage. Notably, the refractive index exhibited a trend consistent with the Young’s modulus as a function of the number of cycles. These results highlight the potential of THz-TDS as a promising tool for clinical applications, offering novel opportunities for the early detection of bone microdamage and the prevention of fractures.</p>