At 34, physical therapist Will Harlow works out like someone decades older.

Their goals are very different — his clients are regaining mobility and independence, while Harlow is training to do sports and “look good in a T-shirt.”

But the same basic principles of longevity apply whether you’re 18 or 80.

In his new book, “Independence for Life,” Harlow maps out the four pillars of health that should be baked into anyone’s workout routine: strength, mobility, balance, and healthy bones and joints.

Harlow said one exercise in particular checks all the boxes for longevity and performance, whether you’re a high achiever looking to gain muscle in less time or a fitness newbie trying to build up your health.

You don’t need a gym or much equipment to get started, so don’t wait, Harlow says — the younger you start training for longevity, the more muscle and fitness you can bank for the years to come.

“There’s no such thing as too early. And the earlier you start, the better of a base you build,” Harlow said.

The best all-in-one exercise for longevity

Harlow’s top exercise for all-around health and fitness is the goblet squat, a movement that trains strength, stability, and mobility at once.

The exercise involves holding a weight, like a dumbbell or other heavy object, with both hands in front of the chest (as if you’re cupping a giant drinking goblet, as the name suggests).

That’s it — you don’t need a gym or any experience with a barbell, machine, or other equipment, and the risk of injury is low.

“The beautiful thing about the goblet squat is it’s highly safe because if you get into trouble, you can just drop the weight,” Harlow said.

Goblet squats work the entire body at once, engaging the muscles of the back, arms, and legs as you control the weight. As you squat, the joints of your knees, hips, and ankles are working, too. Plus, positioning the weight in front of your body activates your abs and hips.

Elite athletes and top trainers love goblet squats for building explosive power. For the rest of us, the goblet squat is a simple way to build muscle that’s essential for healthy aging, and mimics real-world activities like sitting down and getting up safely.

“It’s so vital to keep that muscle on our body,” Harlow said. “Strength is just a proxy for independence because if you’re weak, you can’t open heavy doors, you can’t get on and off the toilet unassisted, and you can’t get on and off the floor.”

The longevity ‘sweet spot’

To get the most out of your squat workout, Harlow recommends focusing on a concept called reps in reserve: that’s how many more repetitions you could complete before hitting muscle failure, when you can’t lift anymore.

Research suggests the specific number of reps is less important than challenging your muscles, working until you could barely manage another rep or two if you absolutely had to.

You want a weight you can lift for at least 10 reps, but not more than 20 reps, for the best mix of strength, muscle-building, and health benefits, according to Harlow.

“That’s a nice sweet spot for building muscle. It’s also heavy enough that you’re going to have an impact on your bone density and you’ll improve your mobility as well, but it’s not so heavy that we are elevating that risk of injury,” he said.

Twenty minutes, twice a week — that’s the promise behind The Exercise Coach, where artificial intelligence and robotics are helping people rethink what a workout can look like.

“We always start with a leg press, and we get a really good workout on those hamstrings, the quads, the glutes,” said Erica Bennett, trainer at The Exercise Coach.

The workouts are designed for all ages and fitness levels, but many clients are 40 and older. That’s where maintaining strength, balance and muscle mass often becomes a bigger focus.

The proprietary “Exerbotic” machines first measure your strength and range of motion.

“The machine will then use that to create the workout for you, so that you are always spending the most time under tension and the right amount for you,” said Bennett.

The goal is to keep muscles working continuously while the machine adjusts resistance and movement by staying within the lines of the digital graph above you.

“That’s reducing some of that wear and tear on the joints. That’s creating a little bit of a safer experience, especially for somebody who’s looking at some age-related muscle loss,” said Bennett.

Owner Chris Geiser says the technology is what first caught his attention.

“I love data, I love systems, and this had both of those, but also allowed us to help transform people’s lives, have an impact on their health,” said Geiser.

While the tech drives the workout, every session is still guided by a coach.

The workout may be short, but it doesn’t feel easy.

The studio also incorporates balance and cognitive training to help clients maintain stability and coordination as they age.

“We don’t need to accept a casual decline of muscle mass. We can keep it up with the right level of intensity and the right frequency,” said Geiser.

For anyone who’s fallen out of an exercise routine, Geiser has a simple invitation.

“You might be surprised what your body can still do. We invite you to give it a shot,” he said.

The Exercise Coach studio at 8425 Seasons Parkway in Woodbury, Minnesota, opens Friday.

One-on-one coach-led training is $35 to 45 dollars per session.

Scratch the surface, and you might think women have the upper hand when it comes to longevity. According to data from the Office for National Statistics, here in the UK, we live an average of 3.9 years longer than men.

Look a little closer, however, and there’s a catch. Thanks to a longstanding lack of investment in women’s health research, our underrepresentation in clinical trials and fewer treatment options designed for our bodies, we spend 25% more of our lives in ill health than men.