Crunch (exercise)

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Performing the crunch

The crunch is one of the most popular abdominal exercises. It involves the entire abs, but primarily it works the rectus abdominis muscle and also works the obliques. The exercise also recruits the obliques. It allows both building six-pack abs, and tightening the belly.


A crunch begins with lying face up on the floor with knees bent and feet planted on the ground. The movement begins on an exhale by curling the shoulders towards the pelvis. The hands can be placed behind or beside the neck or crossed over the chest. On an inhale, slowly return back to the starting position. Injury can be caused by pushing against the head or neck with hands.


The difficulty of the crunch can be increased by lying on a declined bench or holding a weight under the chin, on the chest or behind the head. Crunch exercises may be performed on exercise balls. Increasing the distance will also increase the load on the abdominals due to leverage.

The curl-up[clarification needed] is taught by spine biomechanics professor Stuart McGill,[1] and he considers it to be a safer alternative to the crunch, which differs from the sit-up.[2] McGill has done extensive research on the effects of crunch exercises on the back, which can be especially harmful for those rehabilitating their backs from an injury.

The New York Times Health blog referencing McGill in 2009 stated:

An approved crunch begins with you lying down, one knee bent, and hands positioned beneath your lower back for support. "Do not hollow your stomach or press your back against the floor", McGill says. Gently lift your head and shoulders, hold briefly and relax back down.[1]

Strength exercises such as sit-ups and crunches do not cause the spot reduction of fat. Achieving "six pack abs" requires both abdominal muscle hypertrophy training and fat loss over the abdomen—which can only be done by losing fat from the body as a whole.

Differences between a crunch and a sit-up[edit]

In a crunch, the lower back does not lift off the floor

Unlike the sit-up, in a proper crunch, the lower back stays on the floor. This is said by scientific literature[specify] to eliminate any involvement by the hip flexors, and make the crunch an effective isolation exercise for the abdominals.[3]


Suspension crunches

The classic crunch is performed lying on the back on a mat or on a flat bench with the knees bent. Beside this variation, there are many others.

Ab Machine Crunches

This is a good option for those who work out in the gym. The advantage of the machine exercises is that they allow adjusting the load and minimize the risk of performing the exercise with improper form, thus involving the abdominal muscles in varying degrees, so this option is suitable for beginners. There are horizontal and vertical ab crunch machines that differ in the nature of the load they exert on the muscles, that is, the exercise can be performed in a lying or sitting position, respectively.

Incline Bench Crunches        

This kind of crunches recruits the lower part of the rectus abdominis muscle. It is performed lying on an incline bench so that the head is below the level of the legs. This position makes it difficult to lift the body up, so the abdominal muscles get a greater load.

Gym Ball Crunches         

They are performed similarly to the lying-on-the-floor crunches, with the difference that one should lie on the back on a gym ball with the feet on the floor. This variation allows increasing the range of motion by stretching the abs while lowering the body down.

Legs Up Crunches            

This option is performed lying on a flat bench or on the floor with the feet elevated off the ground with a 90 degree bend at the hips and knees. The hips should be positioned vertically and the lower legs – horizontally.

Weighted Crunches

This variation is suitable for those who want to increase the load and make the exercise more difficult. For this purpose, a weight plate or a dumbbell of suitable weight can be used.

Cable Machine Crunches              

One should grab the handle of the cable machine, kneel in front of it, and begin to bend and extend the back. The proper form implies that at the moment of maximum contraction of the abdominal muscles, the hands should be at the back of the head; when extending the body, they should be above the forehead. The hips are kept motionless.

Oblique Crunches            

These crunches work the oblique abdominal muscles. They are performed lying on the back with the knees bent and hands behind the head or crossed over the chest. In the first case, while crunching up, one should bring the elbow towards the opposite knee, and in the second case, the elbows should move towards the thighs.

Reverse Crunches

They are done with the upper back on the floor and lifting the hips up instead. This kind of crunches not only strengthens the core, but also improves the posture.

Thai Crunches

They are performed by hitting the stomach after full contraction. This variation is used by Muay Thai fighters to condition the core to take hits from punches or knees.[citation needed]

These crunch variations differ from one another in the load they exert on the abdominal muscles. Due to the anatomical features of the human body, different kinds of crunches can be more suitable and effective for different people.

The position of the hands and arms is also important. The crossed-arms crunch is easier, so it is suitable for beginners. Another option with the hands placed behind the head is more difficult and is usually used to increase the load. One more complicated option is performed with the straight arms extended forward above the head and the wrists crossed.

Number of Reps[edit]

The number of reps and the intensity of load are chosen according to the workout goals. If the goal is to build six-pack abs, one should perform three or four sets of 8 to 15 reps. Additional weights in the form of a dumbbell or a weight plate can be used to complicate the exercise. In the gym, the load can be increased by doing the exercise on an ab crunch machine.

If the goal is to speed up the fat-burning process in the abdominal area and tighten the belly, the number of reps should be 25 or more. The number of sets should be also increased to five or more.


Crunches are not recommended for everybody. Before mastering the technique of crunches, one should consider the contraindications. They include the presence of:

  • herniated discs;
  • osteoporosis;
  • osteochondrosis;
  • heart problems;
  • respiratory system disorders.

Obviously, pregnant women should not perform crunches.

Common Mistakes[edit]

One of the most common mistakes among beginners is doing body raises instead of crunches. In crunches, the body seems to be hunched and the torso goes toward the hips, but in body raises, the back remains straight and the shoulders go toward the knees. In this case, the abdominals are not engaged at all.

Proper pacing is also important. The faster you perform the exercise, the worse the target muscle fibers work. Besides, the appearance of inertia during the exercise should be avoided.

Another mistake made by many people is tensing the neck and pressing the chin to the chest. This exerts an extra load that should be avoided. Improper breathing is a very common problem. While doing a crunch, a sharp and powerful exhale is needed, to load the rectus abdominis muscle to the maximum extent possible.

Relaxation of the abdominal muscles in the peak extension movement is also a mistake. The effectiveness of the exercise can be increased twofold, if the abdominal muscles are kept in tension throughout the whole range of motion.

Interesting Facts[edit]

According to the study conducted by American scientists from the laboratory of biomechanics at the University of San Diego, the most effective abdominal exercises were selected and assessed depending on the load they exert on the muscles.

In their top-7 exercises, the extended arm crunches are in sixth place, legs up crunches are in fourth place, and the third place is occupied by gym ball crunches.

Captain’s chair crunches and bicycle crunches took the second and the first places, respectively.


Some experts in exercise science doubt whether crunches are necessary for sports training,[4] and others say that even as few as 6–8 crunches per set are enough.[4]

See also[edit]


  1. ^ a b Reynolds, Gretchen (2009-06-17). "Is Your Ab Workout Hurting Your Back?". Well. The New York Times. Retrieved 2011. Check date values in: |accessdate= (help)
  2. ^ McGill, Stuart (2007). Low Back Disorders: Evidence-based Prevention and Rehabilitation. Human Kinetics Publishers. ISBN 978-0-7360-6692-1.
  3. ^ "Are Sit Ups Bad for You? The U.S. Military Seems to Think So…". Retrieved 2018-10-17.
  4. ^ a b Reynolds, Gretchen (August 17, 2011). "Are Crunches Worth the Effort?". Well. The New York Times. Retrieved 2012. Check date values in: |accessdate= (help)

External links[edit]