Chances are, most of us learned to perform a sit-up or crunch at gym class or physical education in school, or in a fitness class. But do you really know how to do a crunch? It's one of those exercise where it's assumed to be common knowledge by everyone – including you – but that doesn't mean you shouldn't take a bit of time to red through this guide and understand the underlying principles behind the move. We'll also highlight some very common mistakes you could have been making all these years.
This isolation exercise (which means "an exercise which targets a specific area") is one that many turn to when trying to tone their midsection, but done incorrectly can lead to all sorts of issues.
That said, when done right crunches are among the best abs workouts you can do and, combined with other moves and lifestyle changes, can be particularly useful if you're trying to lose weight on your stomach.
How to do a crunch
- Getting the crunch right is all about body positioning. Lie flat with your fingertips behind your head, just above your ears. Your elbows should be in line with your chin or ears.
- Your legs should be together, bent at the knees, with both feet placed flat on the floor. They should remain together, flat on the floor, throughout the exercise. Don’t lift your legs!
- To perform the crunch, raise your head and shoulders off the ground, pushing your chest towards your hips. Your ‘abs’ should tighten during the movement. Pause, before returning to the starting position in a controlled manner.
- The crunch is hard to get right, and many people make mistakes. Try not to push your head forward with your hands – the movement for the exercise should come from your abs, spine and lower back.
Why do crunches?
Crunches work the upper abdominals, developing core strength to help you in a wide variety of moves and disciplines. In any physical activity, whether it’s football, boxing, rock climbing or dance, a strong core is vital for anyone undertaking any kind of regular exercise, and particularly those playing sport.
Having a strong, flexible trunk (that’s the area around the abdominal muscles) is vital for success in sports. The abdominal crunch is a classic exercise that works the abs, just like a sit up. However, unlike a sit up, which involves raising your upper body, the crunch is about raising your head and shoulders.
But why do crunches at all, when there’s more complex, all-singing, all-dancing exercises out there? The simple answer is: because they work.
Researchers from the University of Wisconsin (opens in new tab), published by the American Council of Exercise (opens in new tab), found traditional crunches had greater abdominal muscle activation than equipment-based exercises using the Ab Circle Pro, Ab Wheel, or other abdominal exercises like planking, decline bench curls or bicycle crunches (although, along with reverse crunch, this is still a good variation to keep your workouts interesting).
The bottom line is that when it comes to the crunch (sorry), this most basic of ab exercises is also one of the most effective.
How to do a crunch: Common crunch mistakes
“As you come up, tuck in your chin to lengthen back of neck and engage your abdominals,” says Sam Hull, top PT and pilates instructor at F45’s Tooting branch. “Slowly lift your head and shoulder blades off the floor, drawing the ribs down and in, when coming up to a crunch position.”
Focusing on engaging your abs is important if you want to make the most out of the crunch. Hull recommends avoiding tension in your neck and shoulders, staying relaxed in your upper body to allow for maximum range of motion.
The crunch is a time-honoured method of sculpting your abs, but it’s falling out of popularity in some quarters, as some fitness experts theorise the act of curling your spine while lying on the floor risks injury because of the pressure put onto your discs.
A round-up of studies published in the Strength and Conditioning Journal (opens in new tab) says a clear consensus has not been reached, although crunches remain very effective in developing abdominal muscles. Little definitive evidence has been produced since the round-up’s publication in 2016.
If you suffer from any pre-existing back pain issues, it’s best to avoid the exercise in favour of other ab moves like the plank. Otherwise, make sure you use our form tips above and incorporate the crunch into a programme of other trunk-strengthening exercises that do not put pressure on your back.
And finally, if you're trying to lose weight on your stomach, it's important to note that crunches alone aren't enough to get you there. You'll also need to incorporate exercises that burn fat into your workout routine, as well as considering factors such as diet, water and alcohol intake, and your sleep patterns.
Variation: Crunch with raised legs
This is a trickier alternative to the requiring greater core stability and control than the normal crunch.
- Lie flat with your fingertips behind your head. Your elbows should once again be in line with your chin or ears.
- Your legs should be together, bent at the knees, elevated in the air at a right-angle to your torso.
- To perform the crunch, raise your head and shoulders off the ground, pushing your chest towards your hips as you would during the standard crunch. Your ‘abs’ should tighten during the movement.
- Pause, before returning to the starting position in the same way.
Variation: Standing Crunch
If performing crunches and sit-ups on the floor places undue stress on your spine, or tailbone, this variation works your obliques and upper abdominals from a standing position, so your spine is not compressed against the floor.
- Standing with your feet more than shoulder-width apart, place your hands behind your head.
- Raise your left knee up to your chest. Slowly lower your torso (not your neck) so your left elbow comes as close to – or touches – your left knee.
- Slowly lower your knee and stand back upright. Repeat on the other side.
The plank is another move which offers you the ability to tone and train your core without compressing your spine. If you find traditional crunches painful, the plank and the standing crunch will allow you to develop that same core strength.
- Get into a push-up position on the floor, resting on your elbows. Raise your bum so your body forms a single straight line, from your heels to your neck.
- This pose should engage your core strength. Avoid raising your bum too high, as it takes the stress away from your core and places it onto your hands and feet. It might be useful to use a mirror to check your form at first.
- Hold the pose for thirty seconds.
Matt Evans is an experienced health and fitness journalist and News Editor at Fit&Well, covering all things exercise and nutrition on the Fit&Well website. Matt originally discovered exercise through martial arts: he holds a black belt in Karate and remains a keen runner, gym-goer, and infrequent yogi. His top fitness tip? Stretch.