One of the instructors I enjoy taking classes from loves to do a vertical run, then holds the pedal stroke smooth (while grinning ear-to-ear as he watches everyone suffer as their quads burn) then immedately into hill sprints, followed by seated sprinting. Then back up and do it again. Usually we do 12 of them, but often count gets lost and it ends up at like 15.

I take his class just to do those