“Fartlek and other types of tempo runs are a great way of getting your body used to small and frequent changes in pace, whether that be during hilly terrain or because you’re struggling during a particular section of the race,” Nuffield Health’s personal training lead, Nuffield Health, previously said.
Article source: https://www.huffingtonpost.co.uk/entry/how-to-improve-running-pace_uk_69b29064e4b05a3e2aa4797c