Just like we train our FTP in cycling, we also have to train the same equivalent threshold intensity whilst running. Having a high threshold running speed has great transfer to the slower race paces of full-distance and half-distance triathlon. The aim of this session is to develop threshold running, over 4 x 1 mile repetitions. However, we change the pace every 400m to slightly above and slightly below your threshold pace, further stressing your physiology and pushing up your threshold speed.
This is also a great session to do after the bike.