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How To Do Ab Crunches

What Are Crunches?

How to do ab crunches

See all ab crunch variations

Often confused with sit ups, ab crunches challenge the performer to lift their upper back and shoulders off the floor, strengthening the rectus abdominis.

Unlike sit ups where the entire torso is raised, the lower back stays glued to the floor with ab crunches. While this means it uses less muscles than the sit up, it’s still a valid exercise and can be helpful for beginners with little core strength who struggle to protect the lower back in a sit up.

Ab crunches are a popular exercise for those wanting to build a six pack as they isolate the abs. To make this exercise more challenging, you can progress to dumbbell or cable ab crunches, or use the ab crunch machine. You can also try side crunches to target the obliques.  

Check out some of our other ab exercises: Side planks, Plank knee to elbow, Plank to press ups, Swiss ball pikesSwiss ball circles

Most Commonly Asked Questions About Crunches

  • Everyone has abs, or abdominal muscles, but whether they are visible is mostly dependent on whether there is fat covering these muscles. Crunches can help to strengthen and define the abs to create that six pack look, but a lot of people will need to also prioritise fat loss to reveal the abs.

  • Doing ab crunches will not burn a lot of calories as there isn’t much movement. It’s better to think of resistance exercises like ab crunches as a means of gaining strength rather than burning calories!

  • You should feel some tension in the abs when performing crunches, however if you are experiencing cramps or pain, it may be a sign of injury, overtraining, or simply not being strong enough. If cramps occur, stop what you are doing and allow your body to rest and recover.

  • Side crunches are an ab crunch variation that involve crunching the torso to the side. In addition to the rectus abdominis, side crunches work the obliques. 

  • Hypothetically, side crunches can widen the waist as they strengthen the oblique muscles, which are the core muscles on the side of the waist. However, it would take a lot of training, as well as a calorie surplus, to build muscle mass to a noticeable level, so it’s not worth worrying about.

  • While side crunches are unlikely to widen the waist, they’re also unlikely to give you curves. Side crunches can help to define the core, but the commonly desired ‘hourglass’ figure is better achieved by training the lower body and upper body, to create a wider back with the intent to emphasises curves.

Tips for ab crunches

  • To ensure you're getting the maximum benefit from the core muscles make sure you're not sticking your bum in the air and your back is flat.
  • Don't let your head drop as you perform a plank - ensure your head and neck are in line with your back so you're looking at the floor.
  • Although it's important to concentrate on perfect form, don't forget to breathe as lack of oxygen can cause dizziness or nausea.


How To Do Ab Crunches

  1. Lie on your back on the floor with your knees bent so that your feet can remain flat on the floor.

  2. Cross your arms over your chest so that each hand is touching the opposing shoulder. Alternatively, rest your hands on your thighs.

  3. Begin the reps by flexing your spine to lift your shoulders and upper back off the floor. Think about squeezing your abs and curling your sternum towards your belly button. Your lower back should remain in contact with the floor throughout.

  4. Take a short pause at the top of the movement before slowly lowering yourself to revert to the starting position.

How To Do Side Crunches

  1. Lie on your back on the floor with your knees bent and feet planted on the floor.

  2. Roll on to one side, so that your hip, torso, and arm are on the floor and your legs are on top of one another with knees bent.

  3. Place the hand that is free on your head behind your ear, and lift your head off the floor.

  4. Squeeze your abs and lift your shoulders and upper back off the floor to bring the top elbow close to your knees.

  5. Once all reps have been completed on one side, rotate your legs to the other side to perform the movement again.


If you’re not sure if any of the above exercises are suitable for you, please consult your doctor before you start it. Need guidance on how to perform the exercise? Ask a personal trainer at your gym.