- The main difference between sit-ups and crunches is the range of motion involved in each core exercise.
- Whereas sit-ups require you to move all the way up, close to your knees, crunches only have you move slightly off the ground.
- As a result, sit-ups can activate more muscles than crunches, but they may also present a greater injury risk.
- This article was medically reviewed by Joey Thurman, CSCS, CPT, FNS, a Chicago-based fitness expert and MYX Fitness coach.
- Visit Insider’s Health Reference library for more advice.
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 of the most popular abdominal exercises are 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.
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 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:
- 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.
- Place your hands behind your head or crossed over your chest.
- 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.
- 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.
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 the best option.
Even a small dose of crunches can bring ample 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 one day per week for six weeks saw improved abdominal endurance.
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
- Lie on your back with your knees bent and feet flat on the floor.
- Clasp your hands behind your head. Be sure to clasp loosely so you don’t pull on your neck during the move.
- Slowly curl your shoulders up off the floor, to about a 30-degree angle.
- 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 on to a strength training workout about two to three times a week. Try for three sets of 15 crunches.
Though both sit-ups and crunches can strengthen your abdominal muscles, crunches are a more targeted approach that focus 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.
It should be noted that alternative core exercises offer similar, and sometimes better, results. For example, a 2010 study published in the Journal of Orthopaedic and Sports Physical Therapy 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.