The objective of this study was to develop a nondestructive indentation technique to quantify the degradation of the material properties of the annulus fibrosus (AF) resulting from nontraumatic cyclic fatigue and to analyze the data in both the time domain, with the relaxation ratio, and the frequency domain, with a parametric autoregressive model. Methods: In this study, 7 human cadaver intervertebral discs were included (4 from L3/4, 3 from L2/3) with a mean age of 52 years (range, 35-61). The relaxation indentation test was applied with an MTS 858 materials testing system using 2.5 mm hemispherical indenters on the posterior disc. Computational analyses, separated into time and frequency domains, were undertaken with an IBM-compatible computer using custom-designed software based on the Matlab (Mathworks, Natik, MA) programming environment. Results: In the time domain, the relaxation ratio averaged 60.7% in the control and 74.4% after cycling. There was a 13.7% increase after cycling. In the frequency domain, the best order of the relaxation function data was one in all specimens. The equation for the specimens was: y(n)-(0.99835±0.0035)×y(n-1)=e(n), where e(n) is white noise. Conclusion: In our hypothesis, the degeneration of the disc arises mainly, in the first step, from mechanical changes in the AF after mechanical loading, followed by an induced sequence of mechanical and biological changes. Microtrauma of the AF because of repetitive or sustained loading will cause plastic deformation of the AF, leading to a vicious cycle of disc degeneration.