Hills that take two to four minutes to climb can serve many of the purposes of VO2 max workouts. And of course if you’re preparing for a long race with several hills, like the Boston Marathon, you’ll want to be used to sustained uphill efforts.
The tricky thing with hills this long is the jog down. First, you’ll probably be fully recovered by the time you get to the bottom. That’s fine, but you need to be sure you’re running the uphill part hard enough to keep your heart rate elevated high enough throughout the workout. Second, there’s the issue of pounding—jogging down a half-mile hill six times when you’re tired can put a lot of strain on your legs. Stay mindful of your form as you jog down so that you’re not crashing into the ground with every step.