This session is designed to improve your aerobic threshold, which, for most people, is around long course pace. As such, the intensity is kept lower, but the duration of each rep is longer (15–16min in length). We call these sessions up-and-unders, going up above and then under your long course power threshold. This session is just 1 hour 15 min in length, but can be much longer in total duration due to the relatively low intensity. Sometimes, these sessions can build up to nearly 3 hours of total work for the big timers!