For as long as six-packs have been a thing, there’s been debate about how best to sculpt them. And while we’ll likely never know precisely what exercises the Greeks and Romans did to forge the chiseled cores immortalized in their bronze and marble statues, chances are they did some variation of the two exercises underlying the ongoing abs training debate of our times. But in the case of crunches vs sit-ups, which is better overall?
Crunches Vs Sit-Ups: Which Are More Effective?
Viewed with an undiscerning eye, the crunch and sit-up look pretty similar; both place you on your back with your knees bent, feet flat on the floor, and fingertips touching lightly behind your ears. But once you get past that starting position, the two exercises begin to differentiate themselves, explains Beachbody Fitness and Nutrition Content Manager Trevor Thieme, C.S.C.S.
Muscle recruitment
When you do the crunch, you only lift your head and shoulders off the floor, isolating your abs. “But when you do the sit up, you raise your entire torso, requiring you to engage more muscles throughout your core, as well as your hip flexors and rectus femoris [one of the heads comprising the quadriceps],” says Thieme. “But that doesn’t necessarily make the sit-up a more effective core exercise — especially when you consider its potential impact on the spine.”
Spinal impact
When you perform the sit-up, it’s extremely difficult to avoid rounding your lower back as you lift your torso off of the ground. “Research shows that the cumulative effect of such repeated spinal flexion increases your risk of back pain,” says Thieme. The sit-up triples down on that risk by also repeatedly pushing your flexed lumbar spine into the floor and potentially overworking your hip flexors, the resulting tension in which can tug on your lumbar vertebrae.
People often commit the same form flaw when performing the crunch, rounding their lower backs as they contract their abs. “But it’s easier to perform the crunch without flexing your lumbar spine,” says Thieme. “Just keep it pressed into the floor. If you can do that, the exercise doesn’t increase your risk of back pain any more than the bench press, squat, push-up, or any other exercise.”
Belly fat burned
It bears mentioning in the ongoing battle of crunches vs sit-ups that the difference in caloric burn between the two exercises is inconsequential. “You’re not going to burn many calories while performing either one,” says Thieme.
Also worth noting is that neither exercise will help you lose belly fat directly, because your body doesn’t work that way. “You can’t target fat loss like you can muscle growth,” says Thieme, adding that you can only lose overall body fat. “But as your body fat decreases, your abs will reveal themselves.”
Verdict: While the sit-up engages more muscles, the move can potentially place more stress and strain on your spine, making the crunch a preferable exercise — if you perform it with good form (i.e., without rounding your lower back). Otherwise, the crunch is no safer than the sit-up.
How to Make Sit-Ups and Crunches Safer
While the consequences of incorrectly doing either exercise outweigh their benefits, there are form cues and variations that can make both safe and effective.