Kathy Lentz competed in her first triathlon at age 68.

When she decided to do it, Lentz hadn’t run, biked or swum in decades. She hadn’t even been working out — too busy with her job. But after she retired, she started training.

One night as she left to train, her husband asked if she really wanted to go. No, Lentz admitted, she did not.

“But I also knew, because I’ve been through things, that it gets better and you have to push yourself through that fear, through that uncomfortableness,” said Lentz, now 69 and a resident of Stacy, Minn. “My end goal was to be able to do this triathlon. I had to work through the uncomfortableness knowing it would get better.”

Lentz had stepped out of her comfort zone.

“Comfort zone” is the psychological state of low stress and low anxiety that people feel when occupying familiar environments, performing familiar activities. It might sound like a pop-psychology catchphrase, but the idea that emerging from a comfort zone can be beneficial has been around a lot longer. In a 1908 study, Harvard researchers found that mice performed best when experiencing mild — but not overwhelming — stress. Neuro­scientists have found that the brain learns best when stress hormones are mildly elevated.

Lentz has long enjoyed taking on stressful challenges. She enrolled in college at age 41, white-water rafted and cliff climbed at 50, earned a master’s degree at 57 and sky-dived at 63. She repeated the YWCA Women’s Triathlon at 69 and plans to do it again at 70.

“I’ve become a much more positive person by doing the things I’m afraid of,” she said. Each accomplishment has boosted her confidence, as if by successfully leaving her comfort zone she extended its boundaries.

Change is needed

New challenges — returning to the gym after years away, learning a foreign language — can be fun at first, said Susan Neustrom, author of the book “The Comfort Zone Illusion: Leaving Your Comfort Zone Is Not So Hard After All.”

But then comes the stage Neu­strom calls “chaotic confusion.” Performing an activity you haven’t mastered is harder than expected. The temptation to give up is strong.

“I always tell people that chaotic confusion is the best stage to be in,” said Neustrom, who is also a life coach and speaker. “People don’t believe it. But you can move out of it most quickly. You don’t want to stay there.”

By midlife, comfortable habits have had decades to entrench themselves. But midlife also can bring sudden changes — departing children, divorce or widowhood, layoffs or retirement — that essentially shove people from their comfort zones.

“You start to question, who am I if I’m not a mom, if I’m not this position in a company? And when you answer, ‘I don’t know,’ change needs to happen,” Neustrom said.

She speaks from experience. A high-school dropout, Neustrom got a GED at 48 and kept going, eventually earning a doctorate. She likens the process to gradually dismantling a brick wall of fear.

“When I got the GED, it didn’t break down the wall, but it did chip a brick. Through the teeny, tiny hole in that brick, I saw a vision of possibilities. And each time I moved forward in the direction I wanted to go, a little more of that brick came down.”

Such undertakings require courage. And courage is like a muscle that gets stronger when you use it, said Billy Anderson, author of “Your Comfort Zone Is Killing You: Finding the Courage to Be You.”

Exercising courage, he stressed, does not mean eliminating fear.

“You can’t be courageous unless you’re scared. If I’m more courageous than most people, [it means] I’m scared more than everybody else,” said Anderson, who earned outside-the-comfort-zone cred by changing careers from advertising executive to Outward Bound leader. He has sky-dived 101 times, run with bulls in Spain and swum with sharks in Thailand.

“It’s a high — it feels really good to know that you were scared but you went ahead and did it anyway. It’s very empowering.”

How we learn

It doesn’t, however, guarantee an enjoyable experience. Last year, Molly O’Reilly of Mora, Minn., arranged to live in Nepal for six months to further her education as a hospice social worker. O’Reilly was a seasoned traveler, and Nepal is known as a beautiful tourist destination. But experiencing Nepal as a resident was a shock. She saw violence, cruelty, chaos, corruption, danger. People with serious diseases receiving inadequate treatment. Child-labor sweatshops and sex trafficking.

“I thought I was prepared, but I was not,” said O’Reilly, who turns 50 in December. “It was not scary going there, but once I got there, I thought, what have I gotten into? I felt like I had walked off a cliff.”

She drank tainted water that had been sold as purified, ingesting a debilitating parasite. She was bedridden, couldn’t eat and lost 40 pounds. She returned to the United States a month early, where she received an antibiotic not offered in Nepal and quickly returned to health.

“When I came home, I hated it there [in Nepal]. I didn’t have a positive word to say about it. I said I would never go back.”

Since then, her outlook has softened.

The experience was unpleasant, but leaving a comfort zone “is how we learn; it is how we grow,” O’Reilly said. “I would do it again, because it makes us stronger, wiser.”