ORLANDO, Fla. — In no shape to say no, John Tenney listened to his physician.

The married father of two daughters from Orlando, who had ballooned to nearly 290 pounds, was asked to find out the age of every older, large person he saw.

“It was tough, but people I thought were in their 60s were in their 40s,” Tenney said. “That scared me.”

Five years after that unusual doctor’s order, Tenney is more than 50 pounds lighter and usually on top of a bicycle.

Tenney, who created the Orlando Runners and Riders Facebook group that has about 350 members, has done the Cross Florida ride — a 170-mile trek from Cocoa Beach to Spring Hill, near the Gulf of Mexico — three times.

“There was one time last year where I went around and saw him at races five nights in a row,” said Tim Molyneaux, race director for a bicycling time trial near Orlando International Airport that Tenney enters regularly. “That shows some serious dedication for a 50s-something guy who could spend his money and time on so many other things.”

After what Tenney, 58, has overcome, he finds no better value than exercising.

He was diagnosed with reactive arthritis in his late 20s.

“It is asymmetrical,” said Tenney, a New York native whose company does human-resources consulting. “It made everything swell: my left knee, my right ankle, my left hip, my right toe. It was all over the place, weird places. They had me in crutches for three or four months. I had a handicapped sticker.”

Tenney’s doctor at the time told him he would not run again. Not one to accept that prognosis, Tenney started walking, then running a little.

He soon ran three or four days in a row.

“After about two weeks, it was gone entirely,” Tenney said. “It still comes back once in a while, but it is really, really mild — in my fingers or lower back, or something like that. It lasts until I exercise it off.”

Arthritis did not stop Tenney. Neither did the excess pounds weighing on his 6-foot frame.

He has completed the Space Coast Marathon twice, finished triathlons and duathlons and competes in a form of bicycle racing called Cyclocross. At 235 pounds, he does not fit the stereotypical image of an endurance athlete.

“If you ask a lot of people about the things they’ve done, a lot of it was just proving somebody wrong,” Tenney said. “A lot of what I have done was just proving somebody wrong. You get a big satisfaction out of that.

“If someone tells you you can’t do something, then you go do it.”

And don’t stop.

“He just keeps going,” said Kyle Markel, who owns Kyle’s Bike Shop on Primrose Drive. “He goes to a lot of difficult races. He doesn’t always win, and he doesn’t always get on the podium. He certainly doesn’t finish first, but it doesn’t seem to bother him.

“He just likes to complete his race and do his thing on his terms.”

At Team Kyle’s Bike Shop annual meeting last year, Tenney threw two bags full of medals on the table.

“I said, ‘These are mine. How many have you got this year?’ ” Tenney said. “‘Everyone was like, ‘What are you doing this for?’ I said, ‘This fat, old man got all these. How many are you going to get?’

“I just try to inspire them to get involved. One of the biggest things about racing is that people are afraid to do it. They are afraid, ‘Well, what if I am slow? What if I am not as good as I think I am?’

As Tenney has learned, wheels work best when they are spinning.