Double Crunches: Benefits and How to Do Them

The double crunch is an abdominal exercise that combines the standard abdominal crunch with the reverse crunch.

Basics

In a nutshell, you lie on your back with bent knees and bring your knees toward your chest as you crunch your torso up to meet them.

The double crunch is an effective way to contract the entire length of your abdominal muscles and hip flexors with a single exercise. You don’t need any special equipment, although you might consider a yoga mat or other soft surface for comfort.

Muscles involved

The double crunch targets a range of musculature in your core, including the following:

• rectus abdominis
• rectus femoris
• external and internal obliques

Benefits of the double crunch

The benefits of the double crunch involve strengthening your overall core musculature.

In particular, research suggests that the upper and lower rectus abdominis muscles are heavily targeted in abdominal crunch and bent-knee sit-up exercises, which are similar to the double crunch (1).

Furthermore, additional research found that abdominal crunches better activate the rectus femoris compared with similar exercises using the Ab Lounge device (2).

Although standard abdominal crunches don’t involve bringing your knees to your chest, both the standard and double crunches involve flexing your torso, making them comparable exercises in terms of rectus abdominis activity.

Finally, an obvious benefit is that this exercise requires minimal to no equipment.

Summary

The double crunch strengthens multiple core muscles and requires no equipment, though a yoga mat may be helpful. Studies suggest that it’s superior to other popular ab exercises that rely on equipment.

The double crunch is relatively easy to learn. Additionally, you can modify the difficulty depending on your fitness level. The standard crunch and the V-up are two variations that decrease or increase the intensity, respectively.

Basic double crunch steps

You can do a basic double crunch by following these steps:

1. Begin on your back with your knees bent, feet flat on the floor, and hands placed alongside your head with your fingers gently touching the side of your head. Alternatively, you can cross your arms on your chest.
2. Brace your core by engaging your abdominals and visualizing your lower ribs slightly moving toward your pelvis. Your lower back should gently flatten on the floor. Each repetition should begin from this braced position.
3. Slowly raise your knees until your thighs are just past 90 degrees with the floor.
4. As you raise your knees, lift your head and shoulders off the floor and raise your chest toward your knees. At the top of the repetition, your forehead should be around 6 inches (15 cm) from your knees.
5. Reverse the movement until your shoulders and back are on the floor and your feet are flat on the ground.
6. Perform 3 sets of 10–15 repetitions as part of your fitness program.

For an excellent breakdown on the double crunch, check out this video.

Common error: arched low back

Arching the lower back is a common error when performing ab exercises. This position deactivates the rectus abdominis, emphasizes the hip flexors, and may strain your lower back.

Research suggests that the braced abdominal position without a lower back arch is vital for safely performing almost every core exercise (3).

To avoid this mistake, ensure that you’re properly bracing at the beginning of each repetition. If you get too fatigued to maintain the brace and your back starts to arch, stop the set and take a rest before continuing your reps.

Common error: crunching the neck

Another very common issue with crunch exercises is placing your hands behind your head and compressing your chin toward your chest.

According to research, this position places strain on your neck and may even make breathing more difficult (4).

Follow the above instructions carefully to avoid this common error.

Be sure to place your hands alongside your head with your fingers gently touching your temples. Do not cross your hands or interlace your fingers behind your head.

Standard crunch

If you find the double crunch too difficult, you can revert to a standard abdominal crunch. This exercise is very similar to the double crunch, but you keep your feet on the floor.

To perform the standard crunch:

1. Begin on your back with your knees bent, feet flat on the floor, and hands placed alongside your head with your fingers gently touching the side of your head. Alternatively, you can cross your arms on your chest.
2. Brace your core by engaging your abdominals and visualizing your lower ribs slightly moving toward your pelvis. Your lower back should gently flatten on the floor. Each repetition should begin from this braced position.
3. Lift your head and shoulders off the floor and raise your chest toward your knees. Keep your feet flat on the ground throughout the movement. At the top of the repetition, your upper back should be around 8 inches (20 cm) off the ground.
4. Reverse the movement until your shoulders and upper back are on the floor.
5. Perform 3 sets of 10–15 repetitions as part of your fitness program.

The guidelines for avoiding lower back arching and neck compression are the same as for the double crunch.

This video offers an excellent demonstration of the standard crunch.

Dumbbell double crunch

If you have access to basic equipment, the dumbbell double crunch is a great way to add external resistance to the movement.

It’s almost identical to the standard double crunch, except that you place a dumbbell between your feet and hold it there as you perform the crunch.

1. Begin sitting with your knees bent and your feet on the floor. Place a dumbbell between your feet, perpendicular to the length of each foot. The topside, weighted portion of the dumbbell should rest on the top of your feet.
2. Lie on your back with your knees up and place your hands alongside your head with your fingers gently touching the side of your head. Alternatively, you can cross your arms on your chest.
3. Brace your core by engaging your abdominals and visualizing your lower ribs slightly moving toward your pelvis. Your lower back should gently flatten on the floor. Each repetition should begin from this braced position.
4. Lift your head and shoulders off the floor and raise your chest toward your knees.
5. As you raise your shoulders and upper back off the floor, lift your feet and the dumbbell off the floor and bring your knees toward your chest. Keep your feet pressed together to ensure the dumbbell is secure.
6. Reverse the movement until your shoulders and upper back are on the floor.
7. Perform 3 sets of 10–15 repetitions as part of your fitness program. You can use a lighter or heavier dumbbell to adjust the intensity.

Ensure that your back doesn’t arch, and don’t compress your neck.

For a dumbbell reverse crunch demonstration, check out this video.

V-up

The V-up exercise is an excellent option if you can easily perform 3 sets of 15 double crunches. The overall mechanics are very similar, but your legs and arms are straight throughout the exercise as opposed to bent.

To perform the V-up:

1. Begin on your back with your arms extended overhead and your legs straight.
2. Raise your arms and legs 6–12 inches (15–30 cm) off the floor and brace your core by flexing your abdominal muscles and slightly bringing your ribs to your pelvis. Your lower back should gently flatten along the floor.
3. Squeeze your feet and thighs together.
4. Raise your legs and torso in a controlled manner and reach for your toes with your hands. At the top of the repetition, your torso and legs should form a “V” shape. If you can’t quite touch your toes, don’t worry — just get as close as you can.
5. Slowly reverse the movement to return to the start position. Ideally, you shouldn’t let your feet or shoulders touch the floor between repetitions.
6. Repeat for 3 sets of 6–12 repetitions.

The form cues for avoiding a low-back arch apply to the V-up.

Neck strain is usually less of an issue, as you’ll not have your hands on your head. Just be sure you keep your chin in the same position relative to your torso and avoid “reaching” with your head or neck.

Refer to this video for a breakdown of the V-up exercise.

Summary

The double crunch is easy to perform and can be made easier or harder depending on your current abdominal strength and access to dumbbells. Be sure to avoid an arched lower back or compression of the chin into the chest.

The double crunch and its variations are excellent ways to strengthen your entire core in a single exercise.

Nevertheless, they have potential downsides for those with lower back issues.

Specifically, scientific research shows that high activation of the rectus femoris (hip flexors) may trigger pain in people with lower back issues. If you struggle with lower back pain, consider avoiding exercises that activate this muscle if they cause any discomfort (5, 6).

If you find your lower back hurting during crunch exercises, try an abdominal hollowing exercise instead.

Summary

You should avoid the double crunch if you have lower back issues. In this case, an abdominal hollowing exercise is a better option.

The double crunch is an excellent ab exercise to target a range of muscles in your trunk and core.

You can perform it with minimal to no equipment and easily adjust the difficulty level.

If you have any lower back issues, you may need to avoid the double crunch. For otherwise healthy individuals, it’s an excellent addition to your core training or overall fitness program.