I ran 1,700 miles last year.

I know this because I am obsessive about tracking and recording every mile I run. Warm-ups and walk breaks don't count; the only miles worth noting are the ones where my legs are pounding, pushing, propelling me around lakes and up hills, trying their best to squeeze out what remains of my youth and vitality.

Actually, this compulsive behavior pays off. I have never won a race, but I have finished second (once) and third (once), never last, and usually near the top of my age group.

So I have learned that putting in the miles works for me.

Except when it doesn't.

• • •

It's 2 a.m., and I am awakened by a sudden soreness behind my right knee.

When I get up, I can barely walk. Every step down the stairs sends a sharp pain shooting down my stiffening calf. I spend the next four days hobbling like I have a wooden leg.

It's so debilitating that people I hardly ever talk to at work ask me about it.

Welcome to the world of the middle-aged runner.

• • •

I didn't start running until I was well into middle age. I ran my first 5k at age 48, my first half marathon at 49, and my first marathon at 52.

When I started, I had no idea what I was doing. I knew nothing about speed work or endorphins or gels. I could not have told you the difference between pronation and supination. I had never bought anything in a wicking fabric or a $150 pair of tennis shoes or a Garmin …

My friend Molly, who has run 14 marathons, thinks runners go through three stages: When they start out, they try (and buy) anything and everything to figure out how to get fitter, how to get faster — and how to not get injured. Then they start obsessing — fretting when they miss a workout, forcing themselves to run even when they're hurt, and (in her case) constantly tying and retying her shoelaces before a race. Then, from experience, they gain acceptance: There are things you can change, things you can't.

Only now, they know the difference.

• • •

There is no shortage of advice for runners. Read the magazine! Buy the book! Follow the training plan! Try the diets and the drinks! Get completely, utterly confused!

I have learned that the only insights of any real value are your own.

I have learned what I can and cannot do, what seems to work and what doesn't seem to make any difference. Sometimes I have surprised myself by achieving way more than I thought possible. And then just when I thought I had it all figured out, I get blindsided (that random calf injury again).

In running, as in life, experience is everything. So we asked Twin Cities in Motion, the organizers of the Twin Cities Marathon, to put us in touch with Minnesota runners 55 and older who have completed at least one marathon and have signed up for this year's race. Then we asked them to share some of the lessons they have learned as midlife marathoners.

Their stories start on page 16. Ø

Paul Duncan is editor of The Good Life.