How to Do Knee Crunches

Co-authored by Dean Theriot

Last Updated: April 28, 2021 References

Knee crunches are a great way to build up your abdominal muscles and strengthen your core overall. If you find that doing traditional crunches hurts your tailbone, try knee crunches as a substitute exercise. Knee crunches focus on the same muscle group as other forms of sit-ups and crunches, but to perform them, you lie flat on your back and, instead of sitting up, bring your knees up towards your face.

Method 1

Method 1 of 3:

Doing an Elbow-to-Knee Crunch

1
Lie with your back flat on the ground and your legs raised. For the sake of comfort, lie on a carpeted section of floor or on a yoga mat. Bend your legs and draw up your knees until they’re directly over your pelvis. Bend your knees at a 90-degree angle so that your feet are sticking straight out.^{[1]
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- This style of elbow-to-knee crunches are great to use if you’re a beginner to fitness and exercising. They’ll build up your abdominal muscles but aren’t particularly challenging to learn.
2
Hold your hands behind your head and look toward your stomach. To get your torso into position for elbow-to-knee crunches, stretch your arms up behind you. Then, bend your elbows and hold both hands behind your head. Bend your neck so that you are looking down your body towards your belly button.^{[2]
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- Try interlocking your fingers behind your head to support your head and keep your hands in place.
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3
Contract your abs and bring your knees up to your elbows. Keep your chin down and tense your abdominal muscles. Keep your abs activated the whole time while you're doing the exercise.^{[3]
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Expert Source

Dean Theriot
Personal Trainer
Expert Interview. 22 January 2021.} To do a crunch, keep your elbows in place and lift your knees upward until your elbows and knees touch. You should feel a slight burn in your lower abs as you touch your elbows and knees together.^{[4]
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- Make sure that you’re engaging your stomach muscles and not just pulling on your head with your hands. You can damage your neck if you pull your head up rather than using your abdominal muscles.
4
Lower your body back to its starting position. After you’ve completed 1 crunch, slowly relax your abdominal muscles and lower your head back down to the ground. Also lower your knees until they’re again directly above your pelvis.^{[5]
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- Relaxing your body slowly will keep your abdominal muscles engaged for longer than they would be if you quickly relaxed your muscles.
5
Do 9 more elbow-to-knee crunches to complete 1 set. After laying back flat on the ground, again clench your abdominals and bring your knees up to your elbows. Complete 9 more crunches in a row to do a set of 10. If you’re just starting out and don’t have very strong abdominal muscles, 1 full set might be as much as you can do. As you gain muscle, try completing 2, 3, or even 4 sets.^{[6]
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- Take a 60-second break between each set of crunches to allow blood and oxygen to return to your abs.

Method 2

Method 2 of 3:

Performing Knee Pull Crunches

1
Lie on your back and cross 1 ankle over the other. Interlace the fingers of your hands and place them behind your head. Lie back on a soft, flat surface like a yoga mat or carpeted section of flooring. Extend both legs in front of you and cross your right ankle over your left.^{[7]
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- Wear flexible clothing while doing knee pull crunches. For example, yoga pants or sweat pants would work well.
2
Tense your stomach muscles and bring both legs up to your chest. Engage your abs and bring your head up so you’re looking down at your stomach. Separate your legs (don’t keep your knees together) and bring both knees up until they’re almost touching your chest. Hold the pose for 3–5 seconds and then relax back to your starting pose. This is a great workout for your lower core.^{[8]
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- Unlike elbow-to-knee crunches, your elbows and knees do not touch each other during knee pull crunches.
3
Perform 2–3 sets of 10 knee pull crunches each. Begin each crunch from your starting position: flat on your back with ankles crossed. Tense your abs, keep your legs apart, and draw your knees up to your chest. As your perform the crunches, you should feel the burn in your lower abs and core muscles. Give yourself at least 1–2 minutes between each set of crunches so your muscles can relax.^{[9]
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- If you’re new to fitness and exercise, you may find that you can only manage to do 1 full set at first.

Method 3

Method 3 of 3:

Doing Cross-Body Crunches

1
Lie flat on your back with your hands behind your head. Do this on a surface that won’t hurt your back, like a yoga mat or a bed. Interlace your fingers and use both hands to support your head. This exercise is a variation on the standard knee crunch and works your obliques more than other varieties of knee crunches do.^{[10]
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- Your obliques are part of your abdominal muscles. They’re located on the outer sides of your torso and run from your waist to just under your armpits.
2
Raise your legs so your calves are parallel to the floor. Lift up your knees so that your legs are bent at a 90-degree angle at your hips. Extend your lower legs out in front of you so that your calves are parallel to the ground and your feet are in midair.^{[11]
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- This is the starting position from which you’ll begin doing crunches. You’ll also return to this position after every crunch.
3
Twist your body by bringing 1 knee to the opposite elbow. Bend your left knee so that your calf and thigh touch and fully extend your right leg. Flex your abdominal muscles and bring your left knee up to touch your right elbow. Keep your shoulders low to the ground as you’re bringing your knee to your elbow, so that all of the work is being done by your abs and core muscles. Hold the crunch for 2–3 seconds.^{[12]
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- Return to your starting pose after touching the knee to the elbow.
- Keep your lower back pressed flat against the ground. You shouldn't have any space between your lower back and the floor.^{[13]
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  Expert Source
  
  Dean Theriot
  Personal Trainer
  Expert Interview. 22 January 2021.}
4
Repeat the crunch by bringing your other knee to its opposite elbow. This time, bend your right knee and bring it up towards your chest. Fully extend your left leg. Flex your abs and rotate your core to the right so that your left elbow touches your right knee. Hold the crunch for 2–3 seconds and then return to the starting pose.^{[14]
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- You should feel a slight burn on your sides as your perform the crunches.
- Try performing 10 crunches in a row. To give your obliques a good workout, do 2 or 3 sets of 10 crunches each.^{[15]
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