I'm in my 70s, I exercise differently than I did when I was younger. I enjoy paddleboarding and yoga instead of running marathons.

• When I was younger, I was competitive and ran marathons. I also cycled and enjoyed rock climbing.
• As I've gotten older, I've let go of the need to prove myself.

In 1987, I ran the Big Sur Marathon, whose inspired pitch, "Run Along the Edge of the Western World," was irresistible. It was my personal best of the three marathons I had run at the time, clocking in at 3:56.

Running races was typical for me in my 30s when I was highly competitive, achievement-oriented, and needed to prove myself.

I focused on running, cycling, and rock climbing when I was younger

My husband Barry and I also bicycle-toured for years in Europe. I remember how fun it was one year in the Pyrenees, cycling in and out of France and Spain, climbing up to one pass, enjoying the breathtaking views, then zipping down to a charming village. The only trouble was that after our glorious descent, we'd face yet another hill to climb. We cycled uphill and down for two weeks straight. I'm glad that era is over!

Same with climbing Mt. Shasta in northern California, where, as I trudged up the intimidatingly steep icy slope in ill-fitting borrowed crampons, I seriously wondered if I might fall off the face of the earth. "I think I'll pass on Everest," I said to the other hikers when I reached the summit. Their laughter was the best part of the whole climb.

And I'll never forget the women's rock climbing class taught by a lithe, silver-haired woman named Annie. We were climbing a rock face above McCabe's Beach in Marin County. About halfway up the rock, I glanced behind and noticed we were the only clothed humans in sight. A bunch of nude men were playing volleyball and waving at us. Later, we realized it was not only a nude beach, but a gay hangout, because we couldn't see any other women besides ourselves.

Now I have a very different approach to fitness

During my 60s and 70s, I developed a radically different set of priorities. First, I do whatever I can to avoid falling. Three broken joints are more than enough. The first is a seriously compromised ankle from an excruciating landing while skydiving near Mt. Rainier 40 years ago. After my surgery, the orthopedist told me, "I put together everything I could recognize."

Thirty years later, another surgeon said that based on my X-rays, he assumed I'd be on crutches, but because I was so active, my ankle was pretty healthy, despite virtually no cartilage. "But no more running!" he added.

The other two falls were less traumatic. I fractured my pinky when I fell while running down a trail and my wrist when my Teva sandal got caught in a sidewalk crack.

Despite my active lifestyle, I have osteopenia, so I do strengthening yoga, weight-bearing exercises, and the Alexander technique, a mind-body modality that promotes good posture.

I still do hard things

The fact that I'm no longer competitive doesn't mean I'm just lying around. I subscribe to the message of a popular book titled "Do Hard Things." If I'm cycling up a hill, I tell myself, "Don't give up til your legs do!" Or if I feel like heading home while on my stand-up paddleboard, I'll say, "Come on, girl! You're not done yet!"

I spend more time in the water

I used to do most of my movement on land. But in recent years, I switched from running to open-water swimming, which morphed into paddleboarding, now one of my favorite fitness activities. It feels more like a spiritual practice than a form of conditioning, though.

I wander around Humboldt Bay, two blocks from our apartment in Eureka, California, and greet the seals (who look skeptically at this strange vertical being), admire herons, and, during high tide, paddle through an otherworldly slough with tiny crisscrossing waterways. Water is the ideal place to be when "the world is too much with us," as Wordsworth said.

Above all, I keep moving

If I had any advice to offer, it's this: do whatever it takes to keep moving. For myself, I increasingly want to be active outside, preferably in places of natural beauty. One exception is wandering for hours (alright, an hour!) along the over 3,000 windy, souk-like alleys in Guanajuato, the Mexican city where Barry and I live part time. I love these streets so much that I take people on tours.

Like the centenarians whose lifestyle I emulate, I avoid "exercise," which is a modern concept: artificial, timed, and structured. Instead I do what the body longs to do, which is navigate my environment on foot. Heading to the library, the bank, or yoga class, I stride along, singing childhood songs like "I Am A Poor Wayfaring Stranger" and "I Love to Go A-Wandering." Walking relaxes me when I'm tense, focuses me when distracted, and wakes me up when lethargic.

After all, what is a brisk walk but following in the steps of the ancients, joining the long line of bipeds before us, who headed outside, putting one foot in front of the other? The timeless practice of walking steadies and sustains me.