If you’re a little hazy on the difference between sit-ups vs. crunches, you’re not alone. They both strengthen your core, but the details on how they differ and the benefits of each can be confusing.
“The main difference between the two is that unlike a sit-up, in a crunch, the lower back never leaves the floor,” explains Katharine Glazer, CPT. Basically, a crunch is a more targeted and isolated exercise that only works your rectus abdominis (primarily your upper abs).
A sit-up, on the other hand, has a larger range of motion and targets multiple muscle groups at the same time—rectus abdominis, hip flexors, transverse abdominis (deep core muscles), obliques (side abs), and lower back muscles. By raising your torso fully off the ground, you’re recruiting more muscles.
There’s a lot more to know about the great crunches vs. sit-ups debate. Keep reading for the benefits and risks of both sit-ups and crunches, plus how to nail your form and which one deserves a slot in your routine, according to experts.
Meet the experts: Olivia Amato is a certified personal trainer and bike, tread, boot camp, and strength instructor for Peloton. Katharine Glazer is a certified personal trainer. Amanda Hart is a NASM- and ACSM-certified personal trainer and holistic health coach with 12 years of fitness experience. Kristina Earnest, CPT, has more than a decade of experience leading cycling and strength classes and founded Kristina Earnest On Demand.
Sit-ups vs. crunches: Which move is better?
That depends on the muscle(s) you want to target, Glazer says. “Every body has unique demands and requirements, there is no one size fits all.”
- If you’re looking to get the most bang for your buck and work multiple muscle groups at once, then sit-ups have an edge.
- Aiming for intense muscle isolation instead? Crunches could be your jam.
- But, some trainers actually prefer other abs exercises over sit-ups and crunches (more on that soon!).
Benefits of sit-ups
- Work *multiple* muscle groups. Sit-ups help you sculpt your abs (and more!) from lots of angles at once when done with proper form, says Olivia Amato, CPT, a Peloton instructor.
- Improve stabilisation. When you engage your core muscles, you’re improving your balance and steadiness, otherwise known as “stability,” says Kristina Earnest, CPT. With sit-ups, you’re lifting your whole torso from the ground which engages your balance-focused muscles like your abs, hip flexors, legs, back, and neck, adds Glazer.
- Better posture. Sitting and standing a bit straighter is a bonus of engaging all those stabilising muscles, Amato adds.
- Increase flexibility. Sit-ups, when done properly, loosen up both your spine and your hips. That motion helps to increase flexibility, explains holistic health coach Amanda Hart, CPT. Better flexibility snowballs into other perks, like leveled-up performance and fewer injuries.
How to do a proper sit-up
- Lie on your back with knees bent at 90 degrees and feet flat on the floor. Place your fingertips on the back of your ears, with elbows bent and pointing out to the side.
- Take a deep inhale, then exhale as you contract your core muscles and lift your torso off the ground. Continue until your chest is as close to your thighs as possible. (Though if you don’t make it all the way there, no worries!)
- With a smooth and steady motion, inhale as you lower back down to the starting position. That’s 1 rep. Start with 10 reps and add as you feel more confident.
Form tip: “I love doing sit-ups when I have a table to anchor my feet on or a workout buddy holding my feet down with their hands,” says Amato. “This usually ensures proper form because you don’t have to worry about keeping your feet on the ground on top of everything else.”
Sit-up variations to try
Boxer sit-up
- Start lying on your back with your knees bent, feet flat on the ground, and hands in fists at your chest.
- Take a deep inhale, then exhale as you contract your core muscles and lift your torso off the ground. Continue until your chest is as close to your thighs as possible.
- Punch forward, fully extending your left arm with the knuckles facing forward and palm facing the ground.
- Repeat with the right arm.
- Slowly lower back down to the floor. That’s 1 rep.
Sprinter sit-up
- Start lying on back with hands by sides and legs extended straight on floor.
- Explosively sit up, bringing right knee toward chest, right arm back, and left arm forward at a 90-degree angles.
- Reverse the motion with control and repeat on the other side. That’s 1 rep.
Slam ball sit-up
- Lie on your back with your legs bent and feet flat on the ground.
- Hold the slam ball above your chest with your arms fully extended.
- Engage your core muscles and elevate your torso to perform a sit-up. Hold the slam ball overhead as you bring your body up to a seated position.
- Lower yourself back to the starting position, making sure you keep the entire motion controlled. That’s 1 rep.
Benefits of crunches
- Strong upper abs. Crunches isolate the upper abdominals and are great when aiming for high rep counts, says Amato. “I find that crunches are a move I can do continuously because they’re a simple, low-impact exercise,” she explains.
- Easy to master form. “With crunches, you just need to focus on lifting your head and shoulders off of the floor while supporting your neck, so it’s easier to get the move down and perform without feeling muscle pain,” says Amato.
- Low risk of injury. Crunches involve a small range of motion, so the risk of injury is also small. Lift higher up off the ground and your hip flexors might begin to activate, putting stress on the spine, Hart says. The minimal movement required for crunches allows you to strengthen your core without putting strain on your back.
How to do crunches with proper form
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- Lie on your back with knees bent at a 90-degree angle, keeping your feet flat on the floor.
- Place your fingertips on the back of your ears, elbows bent and pointing out to the side.
- Take a deep breath in, contract your core muscles, and then lift only your head and shoulder blades from the ground, exhaling as you rise. (Keep your chin tucked, but not touching your chest, and let your head be heavy in your palms to put more work into your abs.)
- Inhale as you lower to starting position. That’s one rep. Start with 10 reps and, if you feel like you’ve got the hang of things, keep goin’ for 20 to 30.
Pro tip: “Crunches can sometimes feel repetitive, but I find that when they do, I just add a twist—pointing one elbow toward opposite knee—to spice things up or crunch to the beat of a song,” Amato says.
Crunch variations to add to your routine
Bicycle crunch
- Lie on your back with knees at a 90-degree angle and feet flat on the floor.
- Place your fingertips on the back of your head with elbows bent and pointing out to the side.
- Exhale and bring right elbow to left knee while extending right leg straight, rotating torso, and bringing left elbow to touch the ground.
- Inhale as your return to start and repeat on opposite side. That’s 1 rep.
Reverse crunch
- Start lying on back with hands by sides and feet lifted off the ground at a 45-degree angle, toes pointed. Press your lower back into the ground and keep your arms at your sides.
- Brace your core, push down into arms, and exhale as you curl your knees toward your chest until hips lift off mat.
- Inhale and slowly return to the starting position. That’s 1 rep.
Frog crunch
- Lie on your back with your arms extended at your sides.
- Bring your feet into a tabletop position, with your heels pressed together.
- Extend your legs out at a diagonal, keeping your heels close together.
- Bend knees and bring heels back toward your body. That’s 1 rep.
How do other ab exercises compare to crunches?
It’s clear crunches and sit-ups are worth your time, but that doesn’t mean they’re always the gold-standard. In fact, some trainers prefer other abs exercises like planks. Why? “Both crunches and planks have the ability to engage the rectus abdominis and the obliques, however, the plank also targets the erector spinae, glutes, hip flexors, quads, and deltoids, which makes it an excellent compound movement and more bang for your buck,” says Earnest.
What’s more, crunches and sit-ups can put significant pressure on the neck, says Earnest, which you won’t experience as much in a plank.
It’s also worth incorporating rotational core exercises into your routine since they strengthen your lower back, increase mobility, and work the obliques, says Earnest. This includes any exercise with a turning motion of your body such as Russian twists, wood chops, and reverse bicycles.
So, are crunches or sit-ups a better workout?
Both can help you build abdominal strength, and each exercise comes with its own set of pros and cons. Assess which might be best for your skill level and safety, then get to work.
Keep in mind, there’s a greater risk of injury with sit-ups: “The problem with sit-ups is that it’s very difficult to do the exercise correctly without rounding the lower back, which increases stress on the lumbar spine,” explains Glazer.
For this reason, “trainers tend to have their clients avoid sit-ups to decrease the risk of injury,” she says. That’s also why Hart prefers crunches. “There is less flexion and extension of the spine, which means less chance for injuries,” she says.
Crunches are super beneficial when it comes to sculpting the top of your six-pack, but that’s actually *also* their downfall. Crunches *only* target your upper abdominals. “The problem with crunches is that since the hips and legs are stationary, you’re not fully activating the lower abdominals, nor are you engaging the obliques,” Glazer explains.
Bottom line: Crunches and sit-ups both come with pros and cons. And there are a plethora of other abs exercises to consider working into your routine as well.
Madeline Howard is a writer, editor, and creative based in Brooklyn. Her work has been published in Esquire, Nylon, Cosmopolitan, and other publications. Amongst other things, she was formerly an editor at Women’s Health. Subscribe to her newsletter ‘hey howie’ at madelinehoward.substack.com.
Andi Breitowich is a freelance writer who covers health, fitness, relationships, beauty, and smart living. She is a graduate of Emory University and Northwestern University’s Medill School of Journalism. Her work has appeared in Women’s Health, POPSUGAR, Food & Wine, What To Expect, Cosmopolitan, Men’s Health, and elsewhere. As a former collegiate pole vaulter, she loves all things fitness and has yet to meet a group workout class she doesn’t like.
