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Lying Knee Raises – Pro Tips on Proper Form and Mistakes to Avoid

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What is a Lying Knee Raises?

Lying knee raises are a simple and beginner-friendly exercise that strengthens and develops the rectus abdominis (six-pack). You must lie on the floor, lift your feet off the ground, and bring your knees to your torso.

A notable benefit of the lying knee raise is that the exercise is simple to learn and start doing. Unlike more complex movements, knee raises don’t require exceptional skill or ab strength to do correctly. Another benefit of the movement is that you don’t need any equipment and you can do it almost anywhere, so long as you have a bit of free space. 

Performing lying knee raises is also beneficial for your functional fitness and athleticism. The movement develops your abs, which play a crucial role in torso stability, balance, and spinal health. 

We recommend including the lying leg raise late into your workouts and doing as many slow and controlled repetitions as possible.

Level of Exercise: Beginner

How to do the movement

Step by step Instruction: 

  1. Lie on the floor with your head, entire back, buttocks, and heels in contact with the ground.
  2. Place your hands to your sides with the palms planted on the floor for balance.
  3. Engage your abs, keep your lower back against the floor, and lift your heels a couple of inches off the floor.
  4. Take a breath and raise your knees to your chest as you bend them on the way up. 
  5. Hold the top position for a moment and lower your legs to the starting position as you extend your knees without letting your feet rest on the floor. Exhale on the way back.
  6. Take another breath and repeat.

What muscles does the lying knee raise activate?

The primary muscle group that works during the knee raises is the rectus abdominis (six-pack muscle) (1). Our abs span from just below the ribcage to the pelvic bone, and their primary function is to shorten the distance between the two (2). The muscle group is also essential for torso stability and maintaining an upright posture.

As we tuck our knees to our torso, the rectus abdominis engages and keeps working as we extend our legs and bring them to the starting position.

Tips on Proper Form when Preforming Lying Knee Raises

An essential tip for lying knee raises is to keep the lower back against the floor from start to finish. Doing so is necessary for contracting your abs and forcing them to do all of the work. Arching your lower back lengthens the rectus abdominis, preventing it from doing all the work and instead forcing your hip flexors to engage. 

Another tip for the lying knee raise is to breathe correctly on each repetition and avoid holding your breath. Breathe in before initiating a repetition and exhale as you straighten your legs. Aside from bringing enough oxygen to your muscles, proper breathing is vital for bracing and core stability.

The third tip for the lying knee raise is to perform repetitions slowly, ensuring that your abs do all the work. Raise your legs, bend your knees, hold the top for a moment, and extend your legs in fluid motions, keeping your abs working at all times. 

Our fourth essential tip for good knee raises is to keep your shins parallel to the floor at all points during each repetition. Your shins will be parallel to the floor at the start of each repetition, and you should maintain that horizontal position. Doing so is beneficial for keeping your balance and maintaining consistency of execution from rep to rep.

Variations and Modifications of the Lying Knee Raise

1. Hanging Knee Raise

The hanging knee raise is a more advanced variation of the movement and requires a fair amount of upper body and grip strength (1). Instead of lying on the floor, you have to grab a pull-up bar and hang from it. Once in position, use your abs to draw your knees to your chest, hold the top position, and exhale as you extend your legs.

2. Lying Knee Raise With Crunch

The lying knee raise with crunch is a fun exercise resembling V ups. You’re still lying on the floor and raising your knees to your torso. But, instead of keeping your torso static, you’re also performing a crunch while tucking your knees. Doing so forces your abs to work extra hard, making each repetition more effective.

3. Lying Leg Raise

The lying leg raise is almost the same as a knee raise, apart from one difference: you’re not bending your knees on the way up. Instead, you have to keep your legs straight as you raise them toward the ceiling. The simple modification forces your abs to work extra hard, making the exercise the next step in your ab training progression.

Mistakes to Avoid

Arching Your Lower Back

The most common and limiting error you must avoid with lying knee or leg raises is allowing your lower back to arch. Preventing the mistake is vital for keeping your spine healthy and stopping your hip flexors from taking over the exercise. A simple way to ensure that is to keep your lower back in contact with the floor. As soon as it arches, it will lift off the floor, and you will know that your hip flexors are taking over. The most common cause for that mistake is weak abs, so being conscious of that and working against it will help you develop the necessary core strength.

Doing Reps too Quickly

The second common error with lying knee raises is performing repetitions too quickly. Doing so isn’t necessarily fatal for advanced trainees who know what they are doing, but it can be bad for people new to the exercise. Excessive speed can prevent you from activating your abs effectively and make it easier for you to fall into a lower back arch. The simple solution to the error is to slow down and perform reps slowly, even if that means completing fewer reps per set.

Similar Exercises to Lying Knee Raises

Ab Wheel

Ab wheel roll-outs are a great activity you can perform to strengthen your entire core musculature. The objective is to get down on your knees, place an ab wheel in front of you and grab it with both hands. Once in position, engage your abs and begin to put your weight on the wheel, pushing it to roll forward. Lean forward as much as possible, hold for a moment and move back to the starting position.


man crunch

Similar to lying knee raises, crunches are a simple and beginner-friendly exercise you can do without any equipment (3). The objective is to lie on the floor, bend your knees, and plant your feet flat on the floor. Once ready, engage your abs to raise your upper back several inches off the floor. Hold the top position and return to the floor, exhaling on your way back.

V Up

man jackknife sit up V up bodyweight

V ups are a challenging bodyweight movement that strengthens your abs and improves core stability. The objective is to lie on the floor, engage your core, and raise your legs and torso simultaneously, forming a V shape with your body. Doing so forces your abs to work extra hard, making the movement a great addition to your core training progression.

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