There's some 250-400 meter hills between 6-7% grade at the ends of my faster runs that always leave me out of breathe at the top. I'm not really training for anything these days, just running for the pure enjoyment. At the end of a 10-12 mile run, these hills just wipe me out especially when I like to pick it up at the end. What's the best way to get stronger going up these? Hill repeats at max effort, slow bounding repeats to work the calves, or hilly circuits?