If you ever just feel like a good ol' sweaty cardio run on a treadmill, this routine is just for that! Hill sprints or incline sprints are great for the legs and they are super challenging! They get you uncomfortable real quick. But that's what you want! Get out of your comfort zone and challenge your body and changes will happen.
The inclines are what matters: Keep them at these levels and adjust your speed where needed. These are the speeds that challenge me at these inclines. You can adjust the speed to fit your fitness levels, but keep the inclines as it says!