One afternoon not long ago, a friend and I were talking at her dining room table, and I’ll admit it, we were feeling a bit self-righteous.

We’d gone bowling with her parents, and we both noticed her mom could barely roll the lightest ball down the alley. She struggled with a lot of other tasks, too. We didn’t think of her as an elderly person, but there she was, looking feeble.

“Well,” my friend said, shaking her head, “she doesn’t really exercise.” I nodded knowingly.

The way my friend and I see it, there are two kinds of people: exercisers and everyone else. We — the exercisers — prefer to sweat, not sit. They — we’ll call them “the relaxers” — prefer to read, not run. They think we’re nuts. We think they’re slowly letting themselves wither.

We’ll call this The Great Divide, and my friend and I patted ourselves on the back for being on the right side of it. Then we got up to leave.

“Ouch,” I winced, grabbing at my hamstrings.

“I’m so sore!” she groaned.

And as we hobbled away, we felt decidedly less smug.

Are you laughing at us? Nodding sympathetically? Either way, we’ll hazard a guess: Whichever side of The Great Divide you’re on, you can’t imagine living the other way.

“People internalize an image of themselves as an exerciser or not,” says David B. Coppel, a sports psychologist at the University of Washington.

I used to think people like me — who exercise four, five, six times a week — were crazy. Three years ago, I described my physical condition as being “what you might expect for someone who types for a living.”

But despite the incident at the dining-room table, this article is not going to say exercise is bad for you. Sorry, relaxers.

At times, if you go overboard, it can definitely beat you up. But stick with us as we take a run at some of the biggest hurdles to becoming an exerciser.

• I’m not overweight.

The truth is, getting up and moving is good even if you’re thin.

It turns out being sedentary is a health risk. Period. It’s up there with high cholesterol, high blood pressure, even smoking, according to a 2010 article in the Journal of the American Heart Association. In fact, fitness level is a “more powerful predictor” of survival than traditional risk factors, the journal says. That means an active person who’s overweight can have a better prognosis than a thin, sedentary person.

Exercise can:

• Reduce your risk of getting, or dying from, certain cancers;

• Delay or avert Type II diabetes, as well as reduce your mortality risk if you have diabetes;

• Help maintain your cognitive function into old age.

Studies — including one by the American Cancer Society — have shown that sitting itself can take years off your life. It’s not just that you’re burning fewer calories. It’s that certain bodily processes go silent — processes that do things like regulate your insulin and get the fat out of your bloodstream.

“Excessive sitting,” a Mayo Clinic researcher told The New York Times, “is a lethal activity.”

• But I do exercise … sometimes.