Five forms of the crunch will be described:
basic crunch
modified basic crunch
machine crunch
reverse crunch
twisting crunch
Main muscles worked
rectus abdominis, external and internal abdominal obliques, transversus abdominis, hip flexors, (and the twisting crunch also works the multifidii)
Capsule description
curl your shoulders toward your hips, or your hips toward your shoulders
Exercise for the abdominal muscles is important, and not just for aesthetic reasons. Strong, well-developed abdominals help to keep the lower back strong and resistant to injury because they help to stabilize the spine during many exercises.
Crunches come in two basic types: The basic crunch curls the shoulders toward the hips, and the reverse crunch curls the hips toward the chest. Each works both functions of the rectus abdominis and transversus abdominis—compression of the abdomen, and flexion of the trunk—but only two of the functions of the obliques: compression of the abdomen, and flexion of the trunk. A third function of the obliques—trunk rotation—isn’t worked by most crunches. The twisting crunch employs rotation.
The rectus abdominis (“six-pack”) is one long, flat, continuous muscle that runs from the lower ribs to the groin. While it’s not possible to isolate the upper or lower abdominals, the two sections may respond differently to flexion exercises that require the shoulders to move toward the hips, than to flexion exercises that require the hips to move toward the shoulders.
Trainees commonly get poor results from crunches for two main reasons: many perform excessive reps with little or no added resistance, and most use incorrect technique regardless of their rep count. With correct technique, moderate reps, and progressive resistance, good results will come. But whether you’ll see your abdominal development will depend on how much fat you have covering your midsection.
Preparatory movement
Before every rep of any crunch, tilt your hips so that your lumbar vertebrae are pushed into the floor or mat.
Lie on a mat next to a bench. Bend your knees at a right angle and rest your calves on the bench. Don’t cross your legs. Get an assistant to hold your legs on the bench, use a purpose-built bench with a leg restraint, or brace your feet in some way so that your legs stay fixed to the bench. Cross your hands and rest them on your chest or shoulders. Before each rep, tilt your pelvis so that while your coccyx and sacrum come off the floor a little (that is, your buttocks rise slightly), your lumbar vertebrae are pushed into the floor. Smoothly curl your torso off the floor until your forearms touch your thighs. Pause for a second at the top position, and contract your abdominals hard. Then take about three seconds to smoothly unfurl onto the floor. Maintain the pelvic tilt during the ascent and descent. Once your shoulders are on the floor, pause for a second, again push your lumbar vertebrae into the floor (that is, tilt your pelvis), and repeat.
Don’t hold your breath. Exhale fully before the concentric or lifting phase, and inhale during the descent.
Keep your head and neck in one fixed position throughout each rep, with your chin slightly off your chest.
A common mistake is putting the hands behind the head. This leads to pulling on the head, causing neck irritation. When you require resistance, hold a dumbbell across your chest, with the handle parallel with your shoulders. You could hold small plates on your chest, but large plates will obstruct the proper movement. Once you’ve progressed beyond using small plates, move to a dumbbell. Be consistent with where you place the dumbbell on your mid to upper chest, so that you apply resistance in the same way each time. If you vary the position of the dumbbell, you’ll change the perceived weight of the resistance.
Loading and unloading the resistance can be a problem—because asymmetrical movement is involved in taking a dumbbell from the floor at one side, for example. Have an assistant put the dumbbell directly on your chest, and remove it for you at the end of the set.
The basic crunch with a dumbbell held horizontally on the chest.
Hip flexors, and abdominal work
The hip flexors are involved in most forms of abdominal work, including crunches. (The iliopsoas hip flexors—iliacus, psoas major, and psoas minor—are located deep in the pelvis, and are hidden from view. The other major hip flexor, the rectus femoris, is visible—it’s part of the quadriceps.) The degree of involvement of the hip flexors depends on the technique used. Abdominal work with straight knees may employ the hip flexors to a greater extent than the abs, and should be avoided. By keeping the knees bent, the involvement of the hip flexors is reduced, and the relative involvement of the abs is increased. Substantial hip flexor involvement can produce lower-back problems for many trainees—typically those whose lower backs aren’t strong enough, and who lack sufficient flexibility. Generally, the greater the hip flexor involvement in abdominal work, the greater the possibility of lower-back irritation.
If you’ve had any back problems, use the modified basic crunch for a few months before you consider progressing to the full-range basic crunch. The modified crunch has a reduced range of motion relative to the basic crunch, and involves the hip flexors to a lesser extent. This reduced hip flexor involvement means reduced stress on the lower back. In the meantime, get checked out by a chiropractor, strengthen your abs with the modified basic crunch, strengthen your lower back with back extensions, and work on the flexibility routine.
The hip flexor involvement in the basic crunch is desirable provided the exercise can be done safely. The hip flexors need to be strengthened, too, once the lower back and abs have been sufficiently strengthened. What’s required is balanced strength across the three areas.
Adopt the same set-up as for the basic crunch, although it may not be necessary to have your calves held against the bench. The modified crunch is a short-range exercise. Only about half your spine should come off the floor. Your lumbar vertebrae must retain contact with the floor throughout each rep.
Use a slow ascent and forcible crunch of your abdominal muscles. Hold the top position for a second. Slowly lower your upper back to the floor. Move smoothly at all times.
Don’t hold your breath. Exhale fully before the concentric or lifting phase, and inhale during the descent.
Why sit-ups with straight knees are dangerous
Especially in days gone by, school students and youngsters elsewhere were urged by instructors to perform quick-fire sit-ups with their knees straight, and hands interlocked behind their heads or necks. That technique can be harmful even for youngsters, and is potentially harmful for most adults. Avoid it.
Crunches are safe, relative to sit-ups, because the knees are bent, the hips are flexed, and the lower back is rounded to the rear. As a result, the abdominal muscles pull you up and forward, and the hip flexors help as synergists (not prime movers) to keep the pelvis stabilized at the crucial moment the crunch is initiated by the rectus abdominis muscles.
But in sit-ups with straight knees, the hip flexors are the prime movers as they first pull the lower back into a more arched position (curved to the front), and then they pull the torso up and forward. It’s this initial pull on the lumbar arch that feels uncomfortable, and commonly creates problems.
Perform crunches, not sit-ups with straight knees.
Follow the manufacturer’s guidelines for the set-up.
Smoothly flex the upper half of your spine. Crunch your torso forward, hold the intense contraction for a second, then smoothly return to the starting position. Pause for a second, then smoothly begin the next rep.
Don’t hold your breath. Exhale fully before the flexion phase, and inhale during the extension.
Compare the effect from the machine on your abdominals with that from the non-machine crunches. The latter may be better, because many crunch machines aren’t well designed.
The crunch machine shown on the left has the resistance arms above the chest. The other one has a resistance pad applied against the chest.
Lie on your back on a horizontal bench. Hold the bench behind your head. With straight knees, lift your legs so that they are perpendicular to the bench. Keep your feet directly above your hips, and bend your knees so that they are above your lower chest. Tilt your pelvis so that while your coccyx and sacrum come off the floor a little, your lumbar vertebrae are pushed into the bench. Initiate every rep in this manner. Then roll your lower back off the bench. Hold the top position for a second, then slowly return to the starting position. Pause for a second, tilt your pelvis again, and smoothly move into the next rep.
This is a short-range movement. Maintain the pelvic tilt throughout each rep. At no point should you arch or hollow your lower back.
Don’t hold your breath. Exhale fully before the concentric or lifting phase, and inhale during the descent.
Performing the reverse crunch on a horizontal bench with your feet above your hips and knees bent above your lower chest, provides low resistance. To increase the resistance, straighten your knees but keep your feet above your hips. To further increase the resistance, keep your thighs perpendicular to the bench, and knees bent so that your feet are in front of your hips. Progress until you can perform your target reps with your knees bent at a right angle and thighs vertical. For increased resistance thereafter, perform the reverse crunch on an incline bench, with your head higher than your hips in the starting position.
Remember to tilt your pelvis so that your lower back (other than your coccyx and sacrum) is flattened against the bench prior to each rep—for safety, and to focus the stress on your abdominal muscles.
In all variations of the reverse crunch, don’t jam your head onto the bench, because that could cause neck injury. Maintain a relaxed neck, and keep the strain of the exercise on your abdominals.
The topmost photographs show the least demanding of these three forms of the reverse crunch. If required, the resistance can be further reduced by bringing the knees closer to the chest.
The bottommost photographs show the most demanding of these three forms of the reverse crunch. To make it even more taxing, perform the reverse crunch on an inclined bench, with your head above your hips in the starting position—the photograph on the left page shows the top position. Start with little inclination, and increase the degree of slope gradually.
This crunch variation increases the involvement of both obliques, because it involves rotation of the trunk. The rest of the abdominal wall is involved, too. Because it involves rotation of the trunk, this crunch also works the multifidii. This muscle group is deep to the erector spinae, from the sacrum to the neck, and extends and rotates the vertebral column.
Adopt the same set-up for the basic crunch, and perform the movement in the same way except add a slight twist during the ascent. As you ascend—following a hip tilt, and full exhalation—point your left elbow toward your right inner thigh. Hold the top, slightly twisted position for a second, then as you descend, return to the symmetrical position. On the next rep, point your right elbow toward your left inner thigh, and so on. Just a slight twist is enough to increase greatly the involvement of the obliques. Although there’s asymmetry in this exercise, it’s safe, and necessary.
When you twist to your right, you use your right external oblique, and your left internal oblique. When you twist to your left, you use your left external oblique, and your right internal oblique.
A purpose-built bench with leg restraints, suitable for the basic crunch (illustrated), modified crunch, and twisting crunch.
Prior to each rep of any form of the crunch, remember to tilt your pelvis so that your lower back (other than your coccyx and sacrum) is flattened against the bench, floor, or mat—for safety, and to focus the stress on your abdominal muscles.