Near bed instantaneous turbulent fluctuations can trigger the mobilization of coarse sediment particles. In recent theoretical and experimental studies, impulse has been proposed as the most suitable criterion for predicting the onset of particle movement. Both the magnitude of hydrodynamic forces above a critical level, as well as the duration of such events, exhibit a wide range of fluctuations. Here their product, impulse, is hypothesized to be well represented by an extreme value distribution. The above hypothesis is examined by means of Extreme Value Theory, to analyze data of extreme impulse events obtained from flume experiments. The proposed theoretical distribution is shown to have an excellent goodness of fit, suggesting its usefulness in modeling the impulse content of nearly incipient flow conditions.