The workout routine that leaves this 82-year-old fitness instructor feeling like he’s 50

For Harry King, an 82-year-old personal trainer, it was an arthritis diagnosis that inspired his fitness journey.

When he was in his 60s, a doctor diagnosed him with arthritis in his knees and told him to limit walking. King did as the doctor advised, but the lack of activity caused him to gain weight and feel worse overall, he recalls. King decided to find other ways to move his body, and began exercising regularly on the stationary bike and lifting weights.

Not long after starting his arthritis-friendly workout routine, King was able to work up to hiking long distances. Fitness then became central to his lifestyle, and soon, a second career.

From senior VP to fitness professional

A former senior vice president of sales and marketing for an insurance company, King was always passionate about supporting his team—a passion he has rekindled with his post-retirement work.

“My purpose in life that I identified a long time ago was to help others get better,” King tells Fortune.

Now, as a personal trainer at his local Planet Fitness gym, King conducts one-on-one sessions with clients and teaches strength-training classes.

“I work with a lot of people 50 and above to train them so they reduce the number of falls they have, and work on balance and strength in all areas of the body,” he says.

King is a testament to the power of lifting weights, which improved his bone density and strengthened his arthritic knees. After defying his diagnosis, he now sticks to a regular workout routine that keeps him walking his dog, kayaking, and hiking as much as he wants—in addition to all of the classes he teaches and clients he works with.

Older adult lifting weights at a gym — King lifts weights at least three to four times per week.

King’s workout routine

Depending on the day, King gets tot the gym at 6:00 a.m. or 12:00 p.m. to start his eight-hour shift.

While there, he squeezes in his own workout. He lifts weights three to four days a week, and does 20 to 30 minutes of cardio on the stationary bike to warm up before lifting and on his non-strength days.

In addition to his workouts and the classes he teaches, King loves to take his dog for an hour-long walk or hike for hours in the state park behind his house.

All of this movement leaves King feeling like he’s 50 years old, he says. Nowadays, he has no trouble regularly going on 25-mile hikes.

“The key I think is not chronological age but body age and mental age,” King says. “How do I feel? How do I want to feel? How do I make myself feel? I’m not ready to sit down and not do anything.”

King advises not only to keep moving, but also to find a form of exercise that you love to keep you consistent—that is what he thinks has kept him feeling young.

“The best way to do that is to keep busy, and exercise on a regular basis,” he adds.

older man exercising at the gym — King’s workout motivation comes from knowing that it enables him to keep going for long hikes with his dog.

It’s never too late to get started

King is far from the oldest person at the gym.

“I had one guy that was 92 that was going to start exercising,” says King, recalling a previous client with a weak hip who started to improve after consistent cycling and weight training. “It improved his quality of life a lot—I could see the difference,” he adds.

King strongly recommends everyone, but particularly older adults, work with a personal trainer who can tell you which exercises to do based on your goals and who can ensure you’re using the right form. When King first joined the gym, he was mostly on the stationary bike; but soon, he befriended a personal trainer who clued him into how to get started with weights.

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King believes the foundation of weight training is your core—and not just your abs. Your core also includes your lower back and glutes, so squats and hinges are helping build your core strength and overall stability, he says.

“If you can work on that section of your body, it helps control the rest of your body,” he says.

King recognizes that it’s not always easy for older adults to be motivated to exercise regularly. His trick is to remember that the time he puts in at the gym allows him to enjoy life.

“It’d be easy for me to go home and not do anything. I’ve got a lot of life to live I hope, and I do that by working out,” King says. “I’ve never let being physically [unfit] keep me from doing something I want to do.”

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