From the Coach guide
Hard runs up a hill, with an easy return.
Hill repeats train a hard effort and build strength in your legs.
Warm up easy. Run up a steady hill hard, then walk or jog down easy. Keep the same effort on each repeat.
Plans use hills to prepare for hilly races, or to vary the hard sessions.
A hilly easy run: easy effort on hills, not repeats.
Randomized trial; well-trained distance runners
Both uphill and flat intervals improved how long runners could hold their VO₂ max speed. Flat intervals improved it more.
The trial used a treadmill incline. Hills outside vary in grade and length.
Coach