In this article, we’ll discuss two of the most popular core exercises out there – the sit up and crunch. We’ll identify the main difference between the two exercises, the muscles they target and answer your questions on which one you should include as part of your S&C training.
Sit-ups vs crunches
The main difference between sit-ups and crunches is how much you actually “sit up.” In a sit-up, you lift your shoulders and lower back off the floor until you’re in an upright sitting posture, whereas in the crunch, you only lift your shoulders off the floor, whilst making sure your lower and mid-back doesn’t come off the floor.
Joints worked and ranges of motion
To understand the difference, firstly we must understand what joints and muscles are being used.
| Joint | Movement | Sit ups ROM | Crunches ROM |
| Hips | Flexion/Extension | Medium – High | Minimal – Low |
| Lumbar spine | Flexion/Extension | Minimal | Minimal |
| Thoracic spine | Flexion/Extension | Minimal – Low | Medium – High |
Muscles worked during crunches
The crunch is an isolated abdominal exercise that mainly works your rectus abdominals and oblique muscles to an extent.
- Rectus abdominals – this muscle runs vertically along the front of your abdomen and is responsible for flexing (bending) your trunk.
- External obliques – these muscles are called “the obliques” and are the outermost muscles on the sides of your abdomen. They are responsible for bending the trunk side-ways, forwards and backwards as well as rotating.
- Internal obliques – these muscles are also called “the obliques” and lie between the transverse abdominals and external obliques. Like the external obliques, they are responsible for bending the trunk side-ways, forwards and backwards as well as rotating.
Muscles worked during sit ups
The main muscles worked during a sit-up include:
- Rectus abdominals – this muscle runs vertically along the front of your abdomen and is responsible for flexeing (bending) your trunk.
- Transverse abdominals – these muscles are the deepest muscles within your abdomen, so they are sometimes called “the inner abs.” They “wrap” around the front and side of your abdomen between the bottom of your ribs and top of your pelvis. They’re responsible for protecting and holding your internal organs in place as well as providing stability for the lower back and pelvis.
- External obliques – these muscles are called “the obliques” and are the outermost muscles on the sides of your abdomen. They are responsible for bending the trunk side-ways, forwards and backwards as well as rotating.
- Internal obliques – these muscles are also called “the obliques” and lie between the transverse abdominals and external obliques. Like the external obliques, they are responsible for bending the trunk side-ways, forwards and backwards as well as rotating.
- Hip-flexor muscles (iliopsoas and rectus femoris) – these muscles are responsible for bending at your hip joint when you sit up.
If you place your hands by your head when doing a sit-up, your neck, chest, and shoulder muscles will work when you lift your body off the floor. You can reduce this to an extent, by placing your hands across your chest.
Which exercise is better?
The crunch is typically considered a “better” core exercise when compared to the sit-up, below we’ll explore three reasons why:
- Safety for the Lower Back
The crunch places less demand and strain on your lower back when compared to the sit up, making it a safer exercise. This is because, in the sit up, you have to lift your whole torso off the floor until you’re in an upright sitting posture, which (1) runs the risk of rounding the lower back and (2) places strain on your lower back (and your hip flexor muscles), both which increases the risk of an injury. In comparison, in the crunch, you only lift your shoulders off the ground, so there is less strain placed on the lower back.
- Muscles worked
The crunch is an isolated abdominal exercise, whereas, the sit up works your abdominal muscles together with other muscles including your hip flexors, neck and chest muscles. This means, that if you’re looking to isolate your abdominal muscles, the crunch is better.
- Education on engaging the core
The crunch is a great exercise to use as a tool to educate athletes on how to properly engage their core muscles – check out The Bloom Method article here to learn more.
Despite the three reasons above on why a crunch is typically considered a “better” core exercise than the sit-up, it’s important for us to say that pick which exercise you feel works best for you and that you enjoy, whether that’s the crunch, the sit-up or a completely different exercise altogether.
When should I choose each exercise?
If you would like an isolated abdominal exercise that mainly works your rectus abdominals and oblique muscles or if you get lower back pain or are new to core exercises, then the crunch may be better for you.
If you would like a “multi-joint” exercise that works your abdominal muscles in addition to your hip flexor, chest and neck muscles and if you can hold the correct form, then the sit up may be better for you.
Which is best for developing strength?
Crunches and sit-ups can both be used to strengthen your abdominal muscles, although, sit-ups can also be used to strengthen your hip flexors, chest and neck muscles too.
What is better for abs (six pack) crunches or sit-ups?
Neither crunches nor sit-ups are effective at building a six pack. If you want to be able to see your abs (i.e. have that six-pack appearance), then consider looking into your overall body-fat percentage (please note, a layer of body fat on your abdominals is normal and healthy).
Studies have demonstrated that even doing 7 abdominal exercises for 2 sets of 10 repetitions 5 days per week for six weeks doesn’t reduce abdominal fat (although it does significantly increase muscular endurance of the abdominals), so completing crunches or sit-ups alone isn’t an effective method for building a six-pack.
Are crunches or situps better for weight loss?
Neither crunches nor sit-ups are effective exercises for weight loss, this is because both exercises work a relatively small group of muscles, which isn’t enough to cause you to burn fat, which is needed for weight loss.
More ab exercise articles
Summary
Crunches and sit-ups are two of the most popular core exercises out there. Sit-ups require you to lift your shoulders and lower back off the floor until you’re in an upright sitting posture, whereas in the crunch, you only lift your shoulders off the floor. They both work your abdominals, but sit-ups also work your hip flexors, neck and chest muscles.
The crunch is typically considered a better core exercise when compared to the sit-up, this is because it is safer on the lower back, isolates the abdominal muscles, and is a great tool to educate athletes on how to properly engage their core muscles.
