The major differences between sit-ups and crunches — and which one is best for you

• The main difference between sit-ups and crunches is the range of motion involved in each exercise.
• Sit-ups require you to lift all the way up, while crunches require a slight lift off the ground.

Working your abdominal muscles is important for more than just aesthetic reasons. Having a strong core brings numerous health benefits, like improved balance and stability.

Two popular abdominal exercises include sit-ups and crunches. While the two are frequently referenced interchangeably, the moves are performed in different ways, and they target different muscles. Whereas crunches specifically target your ab muscles, sit-ups activate more muscles than just those in your core.

Here are the main differences between the two exercises and how to do them properly.

Sit-ups

A sit-up is an abdominal exercise that strengthens the muscles in your core — and beyond. The move is particularly effective at engaging the rectus abdominis, the muscle that runs vertically along the front of your torso. Sit-ups also work your hip flexors, the muscles that run from your thighs to your lower back.

However, sit-ups may risk potential injury to your back, because the move pushes your curved spine against the floor, which puts extra pressure on your spine. And because sit-ups also work your hip flexors, these muscles can become tight, pulling on your lower spine and possibly causing lower back pain.

Your risk for injury depends on your body type and medical history, according to Stuart McGill, an expert in lower back disorders and professor emeritus in the department of kinesiology at the University of Waterloo.

Some people have a slender spinal column, and others have a thick spinal column where the vertebrae are simply larger — for example, think of a gymnast versus a linebacker.

"Those people with very heavy skeletons will break into back pain sooner doing sit-ups than those with thinner, more flexible spines," McGill says. "This is because thinner columns have less stress when bending."

Overall, sit-ups are best if you'd like to work more than your abs alone and if you don't have any back, neck, or spine problems that may be aggravated by the exercise.

How to do a sit-up

Follow these four steps to do a sit-up properly and reduce your risk for injury:

1. Lie flat on your back with your legs bent at the knees and feet flat on the floor. Your heels should be close to your butt to create a 90-degree angle at your knees.
2. Place your hands behind your head or crossed over your chest.
3. Curl your upper body forward until it's no longer on the floor and your chest is inches from your thighs. You should feel this mostly engaging your abdominal muscles.
4. Lower yourself back to the floor and resume your starting position. Repeat this move at a slow, controlled pace.

You can incorporate sit-ups into a strength training workout, adding them after you lift weights or do squats. Try to aim for three sets of 15 sit-ups, at least two to three times a week, to get results but also avoid overtraining.

Types of sit-ups

There are many types of sit-ups that you can try. Here are a few options you could add to your next workout:

Jackknife sit-ups

These low-impact sit-ups are great for targeting the lower abs.

1. Lay on a flat surface with your legs out straight, and your arms outstretched overhead.
2. Contract your abs and slowly lift your legs upwards at a 35-45 degree angle. Lift your arms at the same time so that they are parallel to your legs.
3. Lift your head off the floor at the same time, but don't tuck your chin or let your head fall back.
4. Lower down gently and repeat.

Russian sit-ups (twist)

A Russian twist works your abdominal muscles as well as your obliques, shoulders, and upper back.

1. Begin in a seated position.
2. Lift your feet off the floor while keeping your knees bent.
3. Straighten your spine at a 45-degree angle from the floor, making the shape of a V with your thighs and torso.
4. Reach your arms out in front of you and clasp your hands together, interlacing your fingers.
5. Engage your ab muscles and use them to twist to the left, then back to the center, and then to the right.
6. Repeat this set of movements.

Janda sit-ups

The aim of a Janda sit-up is to isolate the abdominal muscles while disengaging the hip flexor muscles. This way, the abs have to work harder. You can disengage the hip flexor muscles by activating your hamstrings and glutes.

1. Elevate the heels of your feet to activate your hamstrings. You can do this by stacking a few floor mats, sitting on top of them, and then wedging your heels on the edge. You could also achieve this by using a resistance band. In this case, thread the band around a piece of stationary gym equipment. Then, insert your heels through the loop of the band on each side.
2. Do a sit-up. As you lift and engage, try to think about closing the space between your pelvis and your ribs.
3. Fully exhale at the top.
4. Lower slowly.
5. Try to squeeze your hamstrings and glutes throughout the exercise.

Crunches

A crunch is an abdominal exercise, similar to the sit-up but with a smaller range of motion. During a crunch, only your shoulders come off the ground, and your lower back stays down.

Crunches work your rectus abdominis and obliques, the muscles along the sides of your stomach. If you're looking to isolate your abdominal muscles for a targeted workout, crunches are an option.

Even a small dose of crunches could bring significant benefits. For example, a 2015 Journal of Sports Medicine and Physical Fitness study found that high school students with no previous training who did crunches between one and three days per week for six weeks saw improved abdominal endurance compared to the control group, who did not do any crunches during that time.

Overall, McGill says crunches put less strain on the spine, so they are especially useful for those who want to target their abs and may be more susceptible to back injury or pain.

How to do a crunch

1. Lie on your back with your knees bent and feet flat on the floor.
2. Clasp your hands behind your head. Be sure to clasp loosely, so you don't pull on your neck during the move.
3. Slowly curl your shoulders up off the floor to about a 30-degree angle.
4. Hold for about one second — you should feel this engaging your abdominal muscles — and then lower back to the ground.

Just like with sit-ups, you can add crunches to a strength training workout about two to three times a week. Try for three sets of 15 crunches.

Types of crunches

The list of crunch variations is long, with new types being added all of the time. Boat crunches, penguin crunches, and standing side crunches all grace the list. Here are a few more mainstream crunch variations you could add to your next workout.

Side oblique crunches

A side oblique crunch can be done lying down. This exercise works the ab and oblique muscles.

1. Lay down a padded floor mat, and then lie down on your left side.
2. Stack your legs on top of each other, with a slight bend in the knees.
3. Bring your right hand to your head, as you would with a traditional crunch.
4. Lie your left arm on the floor, parallel to your body.
5. Brace your core, and then pull yourself up using your obliques, bringing your right elbow up and towards your feet.
6. Pause, and then slowly come back down to the starting position. Repeat for several repetitions before switching to the other side.

Bicycle crunches

1. Lie flat on the ground with your knees bent and feet flat on the floor. Your lower back should be flush with the ground, and your hands should be behind your head.
2. Engage your core muscles, drawing in your ab muscles and stabilizing your spine.
3. Keep your hands behind your head and lift your feet off the floor while raising your knees to a 90-degree angle.
4. Begin the movement similar to pedaling a bicycle. Bring one knee towards your armpit while straightening the other leg.
5. As one knee comes up, rotate your abdomen to try to touch your opposite elbow to that knee.
6. Alternate this twist to the other side and repeat.

Toe tap crunches

A toe tap crunch adds an extra level to the traditional crunch by targeting the upper and lower abs.

1. Lie flat on your back.
2. Lift your arms and legs, so they are extended up towards the ceiling.
3. Lift your upper back as you try to reach your hands to touch your feet.
4. Keep your arms lifted overhead while lowering your legs back to the ground. Your shoulders should stay off the mat, while your lower back should stay pressed to the mat.
5. Repeat this motion.

Sit-ups vs. crunches

Though both sit-ups and crunches can strengthen your abdominal muscles, crunches are a more targeted approach that focuses on your abs, while sit-ups work the surrounding muscles, as well. Crunches may also carry a lower risk of injury, as sit-ups can cause lower back pain for some people.

Are crunches or sit-ups better for losing belly fat?

While sit-ups and crunches can help you build a strong core, they won't reduce your belly fat. A combination of diet, strength training, and cardiovascular exercise is needed to lose belly fat.

Which is better for a six-pack?

Crunches may be better for someone trying to build a six-pack because of the muscle isolation. Sit-ups target the abs as well as the hip flexors, chest, and neck.

How do other core exercises compare?

It should be noted that alternative core exercises offer similar, and sometimes better, results. For example, a 2010 study found that exercises done in a prone — face-down — position on an exercise ball are just as effective, which may be a helpful alternative to avoid back pain.

For example, planks may be the most beneficial core exercise for your health. Not only do they reduce the potential strain on your back and neck, but they also strengthen muscles in your upper body, like your triceps and shoulders, while you hold the pose.

Still, all of these ab exercises can be part of a healthy, effective workout regimen. Just make sure you do each with proper form to reduce the risk of injury and achieve the most benefits.

Insider's takeaway

Both sit-ups and crunches can help you build a strong core. While sit-ups work various muscle groups, crunches isolate the ab muscles, making them a popular choice for people working on a six-pack.

There is a long list of variations for both crunches and sit-ups, which can add some diversification to your workouts. Keep in mind that, like many exercises, both crunches and sit-ups can come with risks like back and neck pain.