Tempo running is a great session to hone a number of physiological determinants specific to long distance triathlon, one of the main ones being running economy. It's also a great skill to train to be able to maintain form at high speed with some fatigue in the legs. This session decreases rep duration, but increases rep pace. Starting at 12 minutes, the rep duration will descend to 8, 4, and then finish with 2 minutes. However the pace will increase from 85% to 96% of threshold pace. Efficient and fluid running is key during this session as you change pace.