Hills are a great way to improve your speed/running economy. They serve the same purpose as 200m or 400m Reps but with added resistance. One downside of doing hill repeats outside is all the impact/stress from running easy back down the hill. A great way to avoid this and mix up your training is to try it on a treadmill.
Below is a sample treadmill hill repeat workout that Dr. Daniels loves prescribing for his athletes. Pictured above, you can see Ryan Hall in the middle of a similar workout from Jack!