Of course not. I started by slowly walk-running 2 miles, two or three times a week and only increased my distance and speed gradually over a period of two years

Of course not. I started by slowly walk-running 2 miles, two or three times a week and only increased my distance and speed gradually over a period of two years (compounded with a couple of frustrating delays due to injuries). These days I run around 25 miles a week - two 6-mile runs during the week and a 13 mile run on Saturday. I also bike around 25-60 miles a week in order to cross-train and give my body a break from running. Before I started, I was 70 lbs overweight with sore knees and a general malaise after two decades of sedentary living and too much food. I'm in much better shape today than I was two years ago, but I was already noticing significant improvement in my fitness, well-being and body shape after just a few months of what now seem like very slow, short-distance runs.