7 of the best ab workout tips we learned from celebrities, trainers, athletes, and bodybuilders in 2021

If there was one recurring piece of advice we heard from fitness experts in 2021, it's this: You can do all the ab exercises you like, but if you're not lean enough through your diet, your abs won't show.

"If you want to see your abs, you have to drop body fat. You can't spot train," Noam Tamir, founder and CEO of TS Fitness in New York City, told Insider.

Bodybuilder Sunny Andrews said getting defined abs is "70% diet."

Hafthor "The Mountain" Björnsson trains hard, but it was only through losing 121 lbs that he first saw a six-pack.

"Diet is super important," he said. "You can train all you want and do 1,000 sit-ups a day, but if your diet is poor, you won't see a six-pack."

It's also important to keep in mind that defined abs don't necessarily mean someone is fit or healthy, and genetics play a big factor, personal trainer Ben Carpenter told Insider.

You don't need weights to develop a strong core and build your abs, Sarah Molloy, a trainer at CrossFit Putney in London, told Insider.

Try dead bugs, single leg V-ups, and Russian twists, or if you're more advanced, push-ups, pull-ups, and ab-dips also rely on core strength, she said.

Actor Henry Cavill said he swears by planks to keep his abs strong, and has done them for years.

"To make particularly aesthetic abs or a strong core, then yes, planks have worked for me," he said.

Cavill does a variety of planks, including standard ones, stability ball planks, planks with shoulder taps, and side planks, he said.

It's important, however, to ensure your technique is on point. A common plank mistake is lifting the hips or collapsing through the shoulders, personal trainer Faisal Abdalla said.

Bjornsson started doing 300 sit-ups a day to build core strength for boxing.

"Sometimes I do 50 then rest for 30 seconds or do push-ups before doing another 50 sit-ups, and sometimes I do 200 or even 300 straight," he said.

It's a mistake, however, to add a twist to sit-ups, according to Abdalla — you should stick to one plane of movement per exercise to maintain tension.

The secret to a strong core, flat stomach, and defined abs is focusing on quality over quantity of movements, according to Jennifer Lopez's former trainer, Johanna Sapakie.

So while The Mountain may do 300 sit-ups a day, you can still get excellent results by doing fewer reps by paying attention to your movements (which is known as the "mind-muscle connection").

"My best advice for a solid core is to do focused, concentrated ab workouts where you are truly aware of what and how your core should be engaging," Sapakie said. "Just knocking out a ton of sit-ups or reps of an exercise without any thought is a true waste of your time."

You don't need to do targeted ab exercises to strengthen your mid-section — compound exercises like overhead presses, squats, rows, and deadlifts all activate your core muscles to help stabilize and control the weight.

Compound lifts are more efficient than crunches or sit-ups alone, since you're tapping into larger muscles groups and burning more calories, Tamir said.

For a super strong core, try holding an L-sit using a set of parallel bars. This is one of CrossFit athlete Sara Sigmundsdottir's favorite core exercises, because they're so hard, she said.

"I close my eyes and think I must have done 20 seconds, but it's only two," Sigmundsdottir said.

Similarly, Andrews swears by hanging leg-raises. "It really engages your lower abs, and with some twists you can engage your obliques," she said.