I've been changing my stride in the last two weeks. I doubled my typical mileage in one week. That's a little extreme. You're supposed to increase by 10 percent a week if your easing into a new pace or stride. I casually run 3 miles to the gym, lift weights, and walk three miles home as a typical workout, but yesterday I ran 6 (which I do once a week) and walked the three miles home. It felt easy and great at the time, but now I can't walk because my calves are solid rods of swollen meat.
But in a months time I'll have strengthened my feet and calves and six miles will be typical and 12 miles will be my long run! I love my new stride, it's the best thing I've done for my workouts in a long time.