Optical fibers should have a minimum life of 25 years. Proof testing is usually done in order to have only high-strength fibers and to evaluate their lifetimes. The behavior of the fibers is studied in terms of the mechanism of slow growth of microcracks. A maximum stress that will be allowed in the subsequent usage of the fiber is then calculated, performing extrapolations from measurements which last a few months to times which last more than 25 years. As might be expected, papers have been published that indicate this procedure leads to inaccurate predictions. Work reported here involves fibers with a broad distribution of strengths. These were used for the purpose of reducing test times. Dynamic fatigue tests were done under atmospheric and inert environments. Results were used to obtain portions of the universal fatigue curve in order to assess the potential accuracy of long-term extrapolation from high-strength fiber tests.224867871