I love fartleks because they develop the aerobic metabolism and they teach athletes to run by feel, which is much better than learning to run by a watch or GPS.
I love long runs because long runs develop the aerobic metabolism, long runs strengthen the mind and long runs improve the athlete’s ability to concentrate while uncomfortable.
I love progression runs for their simplicity. Start a run and speed up as the run progresses. That’s it – just keep speeding up as the run processes. After a successful progression run the athletes has greater confidence in their ability to speed up at the end of a race, to run faster when they’re extremely uncomfortable.