When Jeff Nelson took up running more than three decades ago, he started small. He went a block.

Since then, he’s gone long: 100,000 miles worth. Not all of it was running. About the time he’d run nearly the equivalent of a trip around the world, his knees basically called it quits on him, so he switched to a bicycle and kept right on going.

One hundred thousand miles.

That’s nearly nine miles for every day since that day in December 1980 when a few buddies at the YMCA in Wenatchee, Wash., asked him to join them on their regular jogs through town.

“I thought, ‘Gosh, I’m not in good enough shape to do this,’ ” recalls Nelson.

Nelson wasn’t some out-of-shape slob. Not even close. He weighed 225 pounds, but it was spread out over his imposing 6-foot-4-inch frame, and he’d been active for most of his life. But he wasn’t sure how he’d take to running, so he started conservatively. One block. Then two.

Then he got serious about goal-setting.

On Jan. 1, 1981, he made an entry in his calendar on the distance he ran that day with a group of friends in what they called “the Hangover Run,” ostensibly to atone for the previous evening’s New Year’s Eve parties.

Since then, Nelson has counted every mile he has run, biked, hiked or cross-country skied.

Most of the first 24,000 miles or so — nearly the equivalent of a trip around the world — he did on foot, right up until his knees began to give him trouble. Since then most of the miles have come while riding a bicycle, always logged on those calendar pages.

They’ve come in and around Wenatchee, then in St. Paul, Minn., where he lived while his wife, Carol, studied in seminary school to become a pastor, and, since 2004, in and around Yakima. He has bicycled over nearly every Washington mountain pass reachable by road. He’s ridden the Oregon and Northern California coastlines, and biked across British Columbia. He had pedaled parks and roadways throughout Utah, Arizona and Idaho.

And he kept writing all that mileage down. “I just wanted a record of how many miles I moved my body,” he says. “I value regular physical activity, and I feel really good when I’m doing this. I’m 70 years old, and I can do things a 50-year-old does.”

Last month, he mentioned to the friend he was riding with that he’d be reaching the 100,000-mile landmark on that day’s ride. His buddy, J.D. Sundseth, was flabbergasted.

“I couldn’t believe it. A hundred thousand miles? That’s a lot of cycling,” says Sundseth, who credits Nelson for having been “kind of my mentor” in introducing him to bicycling. “He kind of showed me the ropes,” Sundseth says.

Nelson doesn’t ride his bicycle every day; he says he rides probably five days a week, typically averaging more than 20 miles a ride. His annual mileage goal is 5,200 miles — 100 miles a week.

He has bicycled as much as 110 miles in a day, hiked as far as 30 miles and has run three marathons (with a best of three hours and 22 minutes, a 7:42-per-mile pace). He has day-hiked through the Enchantments, going in over Aasgard Pass and coming out by way of the Snow Lakes trail.

Sometimes Carol is riding alongside him, and sometimes she’s what Nelson calls “my support crew.” But whoever is riding alongside him enjoys it, because, as Sundseth says, Nelson isn’t a hard-core rider focused only on his mileage. He’s telling stories, cracking jokes and enjoying the views.

“He’s an easy friend to be with,” Sundseth says. “He’s kind of like a comfortable old shoe. He doesn’t wear out.”

Evidently not.