Crunches vs. Sit-Ups: Which Exercise Is Better For You?

If you’re trying to build a strong and defined core, you’ve probably done your fair share of crunches and sit-ups. However, what’s the difference? Is one better than the other? As it turns out, crunches and sit-ups both have a place in your workout regimen. So let’s talk about the differences and similarities between crunches and sit-ups and how many of each you should be doing to achieve your ab goals.

Key takeaways:

How are crunches different from sit-ups?

Both crunches and sit-ups start in a similar prone position with your knees bent, feet flat, and upper body on the floor. Both exercises also engage your abdominal muscles, bringing your upper body up off the ground. However, crunches have a much smaller range of motion than full sit-ups since they only require you to get your shoulders up, while sit-ups require the elevation of your full trunk.

As such, crunches more specifically target your abdominal muscles, while sit-ups are better for your abdominal muscles and core muscles.

Both sit-ups and crunches can also be modified for a more targeted burn. For example, you might get a better full-core workout versus crunches or regular sit-ups by incorporating modifications like:

  • Incline sit-ups;
  • Straight-leg sit-ups;
  • Weighted sit-ups.

What are crunches?

Crunches are exercises that work your core muscles, requiring your abdominal muscles to contract to bring your shoulders off the ground.

While crunches are easy to do and can be incorporated daily into your routine, there’s evidence that doing them as little as once a week can increase abdominal endurance. Of course, how many crunches you do in a day depends on your fitness level — as a general rule, start by performing three sets of ten crunches, then progress to five sets as you master the technique.

You can also do different crunch variations to target specific abdominal muscles. Example variations include the following:

Woman doing crunches alt
  • Side crunches. Turn your knees towards one side and “crunch” towards the other, targeting your obliques.
  • V crunches. Extend your legs straight outward at an angle and crunch up to engage your lower abs.
  • Butterfly crunches. Lie back and bring your feet closer to your body until the soles touch, then let your knees outward toward the ground. Crunching in this position targets your entire core since you can’t use your feet on the ground as leverage.
  • High crunches. Reach your hands up toward the ceiling with each ascent to target your lower abs and hip flexors.
  • Penguin crunches. Keep your hands on the ground at your sides and reach forward one side at a time for a lateral crunch that targets the obliques.
  • Twisting crunches. Reach each elbow towards the opposite knee one at a time.

How to do a crunch correctly

  1. Lay on your back with your knees bent and feet flat on the ground. You can use your hands to gently cradle your head or cross them at your chest;
  2. Curl your body up until your shoulders leave the mat with your lower back still on the ground. Make sure your hands aren’t pulling your neck as you ascend — instead, they should just be gently supporting your head and neck;
  3. Slowly return to the start, keeping your core muscles engaged. Repeat.

Benefits of crunches

  • Better for your back. Crunches tend to be safer for your back and neck muscles, especially if you suffer from back pain;
  • More targeted abdominal work. Since the range of motion is so small and isolates your abdominal and oblique muscles, crunches are excellent for building ab definition;
  • Easier for beginners. Many people find that crunches are easier to perform than sit-ups due to the smaller range of motion.

What are sit-ups?

As the name suggests, sit-ups are an abdominal and core workout that involves rising all the way up from the starting position on the ground. Sit-ups work a wide range of both abdominal and core muscles, including rectus abdominis, obliques, hip flexors, chest, and neck.

How many sit-ups should you do a day for results? Start with three repetitions of ten sit-ups, then work your way up to sets of 25 repetitions until you can do 100 daily.

There are also sit-up variations that further challenge your abdominal muscles. However, you can also do different crunch variations to target specific abdominal muscles. Example variations include the following:

Woman doing sit ups
  • Jackknife sit-ups. Lay flat with legs straight out, then sit up bringing your upper and lower body up simultaneously.
  • V sit. Rather than moving up and down, hold your legs and torso at a “V” angle.
  • Incline sit-ups: Use a decline bench with leg supports at the top to bring your entire torso up.
  • Straight leg sit-ups: Start with your legs straight out in front of you and sit up, which will recruit your hip flexors as well as your abs.

How to do a sit-up correctly

  1. Lay with your knees bent and feet flat on the ground. Use your hands to cradle behind your head or cross them across your chest;
  2. Keep your back straight, lift your trunk until your chest almost reaches your knees. (If necessary, ask a partner to hold your feet down). Make sure that you are not using your hands to pull your head forward; instead, keep your spine neutral;
  3. Slowly return to the beginning position and repeat.

Benefits of sit-ups

  • Targets more muscles. Sit-ups are more advanced exercises than crunches, and it requires the activation of more muscles throughout your abdomen to perform correctly and stay stable. Sit-ups also work your hip flexor muscles.
  • Better for your overall core strength. Because it requires a wider range of motion, sit-ups are also great for both your flexibility and your posture, which is helpful both in and out of the gym.

Which is best for abs: crunch, sit-up, or plank?

Ultimately, this depends on your goals, and one is not better than another. However, let's recap and take a look at each:

  • Crunches target your upper abdominal muscles and are good options for beginners or people with back problems;
  • Sit-ups mostly work your abdominal and core muscles, but they also recruit your hip flexors;
  • Planks are core stabilization exercises that are great for strengthening but do not enhance muscle definition. However, core stabilization exercises like planks may be better for your back than traditional sit-ups and crunches.

In short, you should incorporate all three: crunches and sit-ups for definition and targeted abdominal work, and planks for overall core strength.

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