I'm a professional Soldier in my early 40s with a bad back, and I used to HATE running, but I did it because it's my job. Shin splints, sore knees, and the worst of it: back spasms that would take me out for days at a time. These shoes made me run properly for my body. It took about two weeks, maybe a little less to condition my feet to running in them. VERY short runs, like 30 seconds of running, followed by several minutes of walking, to equal a mile of running. And a bit of ice after the run. Six weeks later, I can run four miles in about 35 minutes at a very comfortable pace and NOTHING hurts when I'm running, and NOTHING hurts when I'm done. No, that's not entirely accurate, these shoes make your calves work, and that's where I feel it, but it's a "good" ache, not a "I-just-broke-something" pain. These will not be the last Merrell's I buy!