A month earlier, my 23-year-old minivan broke down for the last time. Rather than replace it, I decided a new “car-free” reality would encourage a healthier lifestyle. My aching muscles questioned the viability of this plan.

Three years later, I now know that giving up my car was the first step toward solving a lifelong struggle: maintaining consistent physical activity. What started as a necessity — I had no car, so I must bike — became a strategy: Errands are an opportunity for exercise.

This reframing turned out to be a motivational bonanza. I began seeking out new errands just for the exercise they would provide. A need for new socks became an opportunity to walk to Target. Running low on Sichuan peppercorns spurred me to cycle the nine-mile round trip to the Chinese supermarket. Earlier this year, I learned that the public library stocked a book about an ancient tomb I was researching, and my first thought was: Excellent, that’s a 4,000-step round trip!

Rain or shine, I became an errand-running machine. My mood improved, my grocery runs got easier and I had to buy a new belt for my shrinking waistline. For most of my adult life, I’d been trying, and failing, to consistently exercise. Only now, as I hit my 60th birthday, did I feel I’d cracked the code.

Experts who study exercise psychology say it was no accident my new errands-based regimen had lasting results. Better yet, what worked for me can work for others.

I am no stranger to motivational gimmicks. After my marriage broke up in the early 2000s, I told myself losing weight would make me more attractive. Mindful of my doctor’s advice about cholesterol, I told myself I was only allowed French fries with dinner if I biked over the nearest hill.

But nothing stuck. Michelle Fortier, a physical activity psychologist at the University of Ottawa, said that outside motivations, like doctors’ warnings and weight insecurities, do not result in lasting behavior change.

“That can get people started,” Dr. Fortier said, “but it will not maintain their physical activity. It doesn’t lead to positive consequences or positive emotions.”

Intrinsically generated motivation, which is driven by a sense of accomplishment or satisfaction, is much more powerful, she said. “You do it because it’s enjoyable,” she said, “And the research shows that type of motivation is good” for exercise maintenance.