December 27, 2021
If you want to achieve a shredded midsection and build up core strength, two of the most classic ab exercises are the sit up and the crunch. Everyone knows them and it would be safe to say everyone has tried them. Whether you do them on a regular basis is another story...
Now, when it comes to sit ups and crunches, people often ask, "what's the difference and which is better?". Some people don't even think of this and just consider the two exercises one and of the same, which is not true.
So, we are here to answer these questions once and for all with a complete comparison of the sit up vs the crunch.
In this article we will cover:
Essentially, the main difference between a sit up and a crunch is the range of motion; in a sit up, you are laying flat on the floor while coming up to a seated position, while a crunch has most of your body remaining on the floor except for the upper back. Crunches are much more isolating to the muscle groups of your core, while sit ups engage a few more muscle groups! Let’s break down what a crunch is and what a sit up is in more detail.
No equipment is needed for a crunch, unless of course you’d like a mat or towel to lay on.
How to do a crunch:
No equipment is needed for a sit up, although you can begin to add weight for added resistance as you progress through your training if desired.
How to do a sit up:
A very common mistake when someone does crunches is performing them too quickly; it’s not an uncommon sight in a fitness center to see someone on the floor knocking out a ton of crunches in a row! However, with speed can come incorrect movement, at least with a crunch. The hip flexors are often engaged with speed on a crunch, removing the emphasis from the torso itself – and therefore reducing the effectiveness of the crunch. This puts the lower back in prime position for injury, since the hips tend to tilt in an anterior fashion. Instead, take your time with crunches; slow and steady wins the race here! Really focus on bringing your torso toward your legs, while maintaining space between the chin and chest (and keeping the neck as neutral as possible).
A common mistake made with sit ups is flopping back down to the ground once you reach the top of the movement; this probably seems obvious, but when you get to the top of the sit up, you want to slowly lower your torso and upper body back down to the ground. This mistake is very similar to that of the crunch – speed can be a hinderance here. Momentum is good, but not in a movement like a sit up! A tip to decrease the speed on the descent is this: think about each vertebrae touching the mat on the way back to the starting position! Not only will this help keep your core engaged, but will significantly slow down the movement (and will allow you to focus on the inhale on the descent as well).
Another very common mistake made with sit ups – and which can cause injury to the low back – is performing the movement without actually curling the torso before executing the top of the movement, or the hip flexion. The hip flexors connect to the lumbar spine, so trying to do a sit up without first engaging the core muscles (bringing the ribcage to the hip bones, in essence) can put a ton of strain on the hip flexors – and therefore possibly leading to lower back pain. In this case, you would really just want to focus on the motion of curling your torso toward your hips before then completing the movement with flexion in the hips.
MISTAKES WITH BOTH CRUNCHES AND SIT UPS:
Pulling your head forward: A common mistake made with both the sit up and the crunch, pulling the head and/or neck forward is usually seen when the movement is new for someone. Essentially, your hands barely support your head as your fingers are interlaced. If you are finding that your hands and arms are doing more work than that (and are subsequently curling your chin in toward your chest, or bearing too much of the weight of your head), then you might find your neck beginning to hurt – or, you’ll find that your core isn’t doing the work it should be in order to lift your upper body or torso off of the floor!
An easy fix for this is to do crunches and sit ups with your arms crossed to your shoulders at your chest.
Feet raising off of the floor: This can be common in both the crunch and the sit up, but more so with the sit up due to the hip flexion at the end of the motion. If anything, try and keep your feet on the floor while you are in the process of engaging your core and bringing the rib cage to your hip bones (the initial curl phase). This way, you can actually focus on those muscles within the core activating properly, instead of immediately having the hip flexors kick in.
It's a somewhat common misconception that sit ups and crunches work the same muscles. While it is true that they target the same muscles, crunches essentially isolate the abs, whereas sit ups work a larger number of muscles.
Let's break it down so you can see what muscles are targeted during sit ups vs what muscles are targeted during crunches.
Rectus abdominis: The main muscle targeted in a sit up, the rectus abdominis runs the length of your torso and aids in torso flexion. This is what we call the "six-pack" (or for some, a 4, 8 or even 10 pack).
Obliques: These muscles are located on either side of the rectus abdominis, and are both external and internal. Obliques aid in torso rotation, as well as bending to the side. The lower back is also supported by the oblique as well.
Transverse abdominis: Located under the rectus abdominis, the transverse abdominis is a horizontal muscle that acts like a corset, aiding in supporting your spine and providing stability to the torso.
Hip flexors: Otherwise known as the iliopsoas, the hip flexors connect lumbar spine to the pelvis and the femur, allowing you to hinge forward (among other movements).
Flexors within the neck: Although most certainly a group of secondary or accessory muscles, the muscles that aid in flexing the neck also take part in a sit up in order to help you lift your upper body off of the floor. This group of muscles can get fatigued quickly, which is why those gently interlaced fingertips at the back of your head can help assist with the weight of your head as you complete the sit up motion.
For crunches, similar muscle groups are utilized; the rectus abdominus, transverse abdominis, and obliques in particular. The crunch, as noted, is more of an isolation exercise, so you won’t be utilizing the hip flexors since you aren’t completely raising your upper body and torso off of the ground like you do in a sit up.
In the grand scheme of things, both sit ups and crunches will strengthen the core. However, the sit up works more muscle groups (primarily the hip flexors) as where a crunch is more isolating to the rectus abdominis in particular. Whether one is best is completely up to you and your exercise programming, as well as your goals. Are you looking to work several muscle groups at once, or do you really want to focus on the isolation that you can get from a crunch? While everyone’s answer will be different, one isn’t necessarily “better” than the other.
Let’s take a look at some history of both exercises and if there are any safety concerns with sit ups or crunches!
Sit ups have been around for a long time – from programming needs for the regular exerciser to soldiers in the army, sit ups have variability throughout many different groups of athletes. This isn’t however, to say that they are better than a crunch – or good for your core at all, if you are dealing with back issues. They are easy to do with a large group of people (elementary kids, group ex classes, the works) so that everyone can all do sit ups at one time…but does this make them okay?
Research has shown a higher number of injuries to the musculoskeletal system when doing sit ups, particularly due to the force that is placed on the lumbar spine from the flexion of the hip flexors. This is especially exacerbated when doing them for time, such as doing as many as possible in a one- or two-minute time frame. (study) Sit ups can be difficult to do correctly if you’re adding speed into the mix; with that being said, paying particular attention to form and technique is key – and avoiding the lower back rounding excessively as well.
Crunches also have some history – after all, step into any big box gym or local fitness boutique and you’ll most likely see some version of a crunch being done! Crunches are an excellent exercise to work into a fitness routine, especially for those who are brand new to exercise. Not only can learning how to do crunches be helpful in regards to learning how to “brace” your core, but they can help increase stability within the muscles of your core as well.
Regardless of whether or not you incorporate sit ups and/or crunches into your routine, know that you will be improving your overall core stability (when the movements are performed correctly, of course). This will lead to improvements in both balance and coordination, as well as activities of daily living! (study)
You may have heard that sit ups or crunches are bad for you. The fact of the matter is, this is not true. If you do a sit up and a crunch correctly, you will be moving your body in a natural range of motion. After all, your spine can bend, if not, how would you ever be able to bend down to tie your shoe!
With that said, a lot of people do sit ups and crunches wrong, such as using their hands to crank their torso up which can put strain on the neck and spine or doing sloppy speed reps. Like with any exercise, if you do it improperly, there will be repercussions.
So, if you are going to do sit ups and crunches, focus on good form. If you do that, not only will you stay injury-free, but you will also build up resilience to injuries of the spine AND you won't need to do so many reps! Several good, slow and controlled sit ups or crunches are going to be far more effective than countless cheating reps, and a lot safer too.
Reps and sets: In regards to both sit ups and crunches, if the goal is endurance, then 2-3 sets of 12-15 reps is adequate. Maximum strength is not typically a goal in regards to core work like it would be in a movement like a deadlift or snatch, where the rep scheme is much lower (6-8 reps). However, if you are new to either exercise, then starting off slow is perfectly fine. Aim for 10 reps of either a sit up or a crunch, and assess how you feel once the movement is complete. These can be sprinkled in throughout your regular workout program, or you can incorporate them at the end of your routine. Taking a break of 30 seconds to a minute between sets will be adequate as well!
Adding resistance: If you have already nailed the proper form and technique of a regular crunch or sit up and you’d like to add some weight to challenge yourself – go for it! These movements can be done while holding a resistance band, medicine ball, kettlebell, or even a dumbbell if desired. Just ensure that you start with a lighter weight in order to make sure you can have complete control over the movement before adding more.
DUMBBELL SIT UPS:
You can also increase difficulty by changing your body positioning, such as decline sit ups or decline crunches.
STABILITY BALL CRUNCH:
This variation of a regular crunch can be a great progression, especially if you want to focus on balance as well. The directions for a stability ball crunch are essentially the same as a crunch on the floor, in terms of mechanics; however, there are some things that need to be tweaked! First, you want to make sure you’re on the right size stability ball – this means your knees will be at a 90-degree angle when you’re sitting up straight on the ball. You’ll want to slowly roll yourself out until the ball is positioned between your shoulder blades and hip bones. Your thighs will be parallel to the floor, with feet shoulder-width apart. Hips can be slightly lower than your shoulder blades here! The movement then follows protocol for a regular crunch, except this time you want to curl until your upper back is off of the stability ball. The kicker for progression here is where your feet are planted; further apart will make the movement easier in terms of balance, while moving your feet closer together will make it more challenging. Play around with it and see where your feet feel most comfortable in order to execute the movement properly!
This variation of a crunch really helps with core stability, and places the focus of the movement mainly on the rectus abdominis. To begin, you want to lay supine on the floor, preferably on a mat. Place your hands at your sides with palms facing down toward the floor, while crossing your feet at the ankles. From here, bring your legs up so that your thighs are perpendicular to the floor (with knees bent at a 90-degree angle). As you engage and contract your core, exhale and press your lower back into the floor and bring your legs toward the ceiling – you should feel your hips tilt ever so slightly. Inhale as you lower your hips back to the floor. This movement isn’t huge, but is a definite burner for the core muscles!
This variation of a sit up is one that will really torch the core – and you hold the position for time, so you can tweak how long you can hold it! In a hollow hold, you begin by laying on the ground in a supine position. Bring your arms up and extend them over your head, while legs are extended straight with feet together. From here, engage the core and bring your shoulder blades down and back as you bring yourself into a slight “C” position – fingertips will be pointed up toward the ceiling while the upper body is raised off of the floor, and legs will be raised off of the ground as you press your lower back into the floor, creating a hollow space with your body. Glutes should be tight here, as should the quads and abdominals. If you’d like to make this movement more challenging, rock yourself back and forth ever so slightly – maintaining that hollow hold throughout your given timeframe.
This core variation can be done in several ways and using different accessories, such as a stability ball – although if you’re just popping down on the floor to do some core exercises, you don’t need anything at all! For a high plank (bearing weight on the hands), you will want to start in a prone position on the ground, preferably hands and knees. From here, bring the wrists in line with the shoulders and have your knees in line with your hips. Your back should be completely flat, with core engaged and shoulder blades retracted. Once you are locked into position, extend your legs out straight behind you so that you are on your toes (and essentially in the prime position for a pushup). The glutes should be engaged, and head in line with the spine. Ensure that you are inhaling and exhaling appropriately, and keeping the core braced. This movement is done for time, so hold on as long as you can while still maintaining proper form and technique.
Related: 29 Great Plank Variations
These are just four of the multiple variations of core work that you can do in place of sit ups and crunches; and in fact, would be wonderful to work into your programming along with those movements! Sit ups and crunches don’t need to be done every day, nor do they need to be done repetitively…instead, having a well-rounded workout that will strengthen and stabilize the core correctly will have you noticing a firmer stomach and better posture in no time.
Both crunches and sit ups are helpful in strengthening the core muscles; while crunches are more isolated to the abs and sit ups target a few more secondary muscles, they both aid in improving your posture, decreasing lower back pain, and improving overall functional fitness in regards to activities of daily living...not to mention, developing some impressive abdominal muscles.
In order to determine which core movement is right for you, take a look at your overall workout programming (as well as your current health and injury status) and see where you can integrate these exercises into your routine. Ideally, you can do both, mixing them up on different training sessions, along with other effective core exercises.
Remember, there should be no pain with either exercise – so if you notice pain (especially through your lower back), stop immediately and speak with your physician to rule out any injury. Outside of that, perform sit ups and crunches slowly and intentionally, and you’ll notice a stronger core and improved posture in no time!
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