AbstractThe purpose of this paper is to present a multiplicative model for the fastest time per year in the 400‐ and 800‐metre races. It is composed of an envelope function and a stationary time series. The proposed model is plausible since there is dependency between the fastest times of successive years and because improvements are expected to be smaller now, as compared with several years ago. Data from the years 1860 to 1988 are used for illustrat