When it comes to one exercise, being board stiff isn’t a bad thing.

“Planks not only enhance core strength but also involve several muscle groups, improving overall body coordination and stability,” explained Phoenix Carnevale, a class experience leader at Life Time One Wall Street in Manhattan with over 20 years of expertise in the fitness sector.

The world record for the longest plank is an astonishing 9 hours and 38 minutes for men, and 4 hours and 30 minutes for women. However, you don’t need to maintain a plank for that duration to achieve noticeable benefits.

The Post consulted with Carnevale to determine how long you should be able to hold a plank at different ages and what it might indicate about your health if you are unable to meet those benchmarks.

Hard core gains

You might picture a six-pack when you think of a strong core, but there’s a lot more going on under the surface.

The central part of your body is made up of 35 muscle groups, including your abs, lower back, hips, glutes, diaphragm and pelvic floor — and planks work them all.

“Being able to hold a plank indicates that you have a strong core, which is essential for good posture, balance and overall physical performance,” Carnevale said.

Regularly incorporating planks into your workout routine can also boost your metabolism, improve your posture, prevent injuries and even support longevity by keeping you mobile and active with age, she added.

“On a mental note, good posture can positively impact your mental health — you’ll stand up tall and proud,” Carnevale said. “The body definitely affects the mind, so standing tall may make you feel more ready to take on the day.”

How long should you be able to plank?

Your age isn’t a free pass to skip out on planks.

A 100-year-old Long Island woman recently made headlines by holding a five-minute plank, while a six month old in Kentucky melted hearts online by holding the position for 34 seconds.

Carnevale said the amount of time you should be able to hold a plank changes with age. She broke it down by decade. 

In your 20s

Aim for a 1- to 2-minute plank.

“At this age, you are very adaptable, making it a great time to build strength and develop healthy fitness habits,” Carnevale said.

In your 30s

Keep that 1- to 2-minute hold going strong.

“Your metabolism may start to slow down, so maintaining core strength is crucial,” Carnevale said.

At this age, longer work hours and more time sitting can do a number on your back and hips, she said but planks can help prevent problems from developing.

In your 40s

Aim for a 1-minute hold or longer.

“This decade is often about maintaining what you’ve built over the years and avoiding repetitive stress injuries,” Carnevale said. 

In your 50s

Shoot for a 30 to 60 second plank.

“As we age, it’s important to focus on stability and strength,” Carnevale said. “Slips and falls can happen, but great core strength keeps you stable.”

In your 60s and above

Try to hold a plank for 20 to 30 seconds.

“Modifications are perfectly okay here, as the key is to maintain core engagement without straining,” Carnevale said. 

Shaking after 5 seconds? Here’s what it means

“If you find yourself unable to hold a plank for the suggested duration, it might indicate a need to strengthen your core and overall fitness level,” Carnevale said. 

But progress takes patience.

“Think of gradual progression — getting a little better each time leads to big results,” she added.

Carnevale recommends starting with shorter holds and building up by adding five seconds at a time.

If you start to waver, distract your mind — sing a song, talk to yourself or find another mental trick to push through, she advised.

“You’ll be surprised at what you can accomplish if you make it a game and have a little fun,” Carnevale said.

Listen to your body

“If someone has an injury, it’s crucial to prioritize safety first,” Carnevale said.

She recommends checking in with a doctor or physical therapist before starting planks. There are plenty of modifications to keep you safe — like doing planks on your knees or using props for extra support.

“Always listen to your body and focus on gentle movements that don’t exacerbate any existing conditions,” Carnevale added.

How to nail the perfect forearm plank

Start face down on the floor. Place your forearms flat, elbows right under your shoulders, arms shoulder-width apart.

Engage your abs, then push up on your forearms, balancing on your toes. Keep hips and stomach lifted so your body forms one straight line from head to heels.

Tighten your core, glutes, and legs for stability. Breathe slow and steady, keep your neck neutral, and eyes just slightly down.

“If you’re looking for more of a challenge, there are always ways to improve,” Carnevale said. Try planking on a stability ball, using TRX suspension bands or adding a weighted vest.

Want a coach? Carnevale leads classes at Life Time One Wall Street and online through the Life Time app — from core and upper body to balance and kickboxing.