Ab In and Outs (Build Core Stability & Strength)

Connor Sellers
Published by Connor Sellers | Senior Coach
Last updated: March 11, 2024
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In my 8-plus years of experience as a certified fitness coach, I've seen most clients target their ab muscles with standard crunches.

While there's nothing wrong with crunches and their variations, they tend to lose their effectiveness with time.

Therefore, you'll need a more efficient ab exercise that will put those tummy muscles to the test. The abs in and outs accomplish just that.

In this article, I will detail my expertise in performing ab in and outs with proper form, muscles worked, and the benefits of these exercises.

Quick Summary

  • To perform the in and out ab exercise, sit with legs extended, tighten your core, lift legs and chest simultaneously, then extend and retract legs while maintaining core engagement.
  • The in and out ab exercise not only targets the abdominal muscles but also engages the hip flexors and quads, making it a comprehensive core workout.
  • The NIH study reveals that the rectus abdominis, key for the '6-pack' appearance, bends the spine and is effectively engaged by In and Out abs exercises, targeting both upper and lower abs.
  • In my opinion, the in and out ab exercise is a versatile and effective way to enhance core strength and stability, suitable for various fitness levels and easily adaptable for home workouts.

How To Do Ab In and Out Workout

A person doing in and out ab workouts at the gym
  1. Begin seated, arms on each side of your body, knees bent, legs extended, and flat on the ground before you. (You can also start with your legs bent in front)
  2. Tighten your core and maintain your back straight as you lift both hands and feet off the floor and bring your right and left knee up to the chest simultaneously. You now have the starting position of the 'in' movement.
  3. Lean back gently while straightening your feet before you, keeping your spine straight. Consider the motion a balancing act between the lower and upper body parts, with your bottom being the sole portion of your body in touch with the floor.
  4. Hold the position (legs straight) as your shoulders approach the floor without letting them or any other area of your body contact the ground apart from your bottom. This is the starting position of the 'out' movement.
  5. Raise your shoulder blades and return your right and left leg simultaneously to the starting position (the 'in' position). Remember to maintain your core tight the entire time.
  6. Repeat the in and out movements for the required number of repetitions.

Learn More: Do Ab Exercises Help Burn Belly Fat

What the In and Out Ab Workout Is

A person doing ab workouts at home

The in and out exercise is an ab exercise that works the abdominal muscles, hip flexors, and quads.

This exercise is primarily designed to isolate abdominal muscles and may progress or regress in various ways.

I've observed that the classic in and out abs exercise presents a challenging yet rewarding experience for my clients. It rigorously tests their muscle strength, body coordination, and stability.

Through consistent training and dedication, many of my clients gradually develop the core strength required to master the full in and out posture, although this achievement often requires considerable effort and time.

When performed correctly, this action and its full-body involvement will benefit the entire body.

This workout has the added benefit of being incredibly accessible because it involves no equipment and may be done anywhere.

Muscles Worked by In and Out Ab Workouts

A person with good ab muscles on the ground

In-and-out abs exercises work primarily on your abdominal muscles in the core area.

Proper form necessitates lower back strength, while hip flexors enable 'in' and 'out' movement.

As you straighten and bend your legs, your quads will also be stimulated.

Through my experience, I've learned that to truly feel the advantages and develop and tone the muscles involved, it's crucial to consistently and routinely include these movements in their workout regimen.

"You'll also want to avoid overworking your core, so give your muscles enough time to recuperate by giving them a day off. If you're including the exercise within a larger workout, be sure the other movements don't also target your core."

- Tatiana Firpo, National Academy of Sports Medicine (NASM) Certified Personal Trainer

The muscles worked:

  • Transversus Abdominis: According to the National Institute of Health (NIH), the fibers of the transversus abdominis run horizontally from the pelvis and ribs, wrapping all through around the trunk [1]. The transversus abdominis stabilizes the trunk while contracting to provide intra-abdominal pressure.
  • Rectus Abdominis: The most prominent muscle in your core and the notably obvious 6-pack in lean people. It is flat against the front of your abdomen. According to the NIH, the basic function of the rectus abdominis is to bend your spine [2]. The in and out abs exercises work both the lower and upper sections of the upper body (the lower and upper abs).
  • Obliques: As noted by the NIH, these muscle groups are in charge of turning and flexing your spine laterally [3].
  • The Iliopsoas: According to NIH, it is the primary hip flexor muscle, and it is further subdivided into the iliacus and psoas main muscles [4]. These muscles, referred to as the hip flexors, work to assist in shifting the legs into place during ins and outs.
  • Rectus Femoris: As NIH notes, among the four quadriceps muscles, it collaborates with the hip flexors to flex the hips throughout in and out movements [5]. To maintain the legs under control during the exercise, activate the quadriceps and keep the legs close together. This enables a seamless transition from one rep to the next.

Benefits of Abs In and Out Exercises

A person doing abs in and out workouts at home

In and out abdominal exercises are worth incorporating into your core training.

Here are the benefits of performing the in and out movement.

  • Strengthens the core: Strengthening and isolating the core muscles results in stronger functional movements in and out of the fitness center. A strong core is also beneficial to balance, posture, and stability.
  • Hip strengthening exercise: Sitting for lengthy periods might cause inactive and weak hip flexors. The hip flexors are critical in obtaining a correct in and out posture. Developing these muscles will result in better lower-body muscular connectivity.
  • Accessible bodyweight workout: The in and out is common due to its simplicity and practicality. You can execute this technique almost anywhere without any special equipment. This movement's regressions and progressions also encompass several popular bodyweight workout alternatives.
  • Enhanced flexibility and mobility: Regularly performing in and out ab exercises increases flexibility and mobility in the abdominal region. This improved range of motion can lead to more efficient movement patterns and reduced stiffness, particularly in the lower back and hips.
  • Calorie burning and weight management: While primarily targeting the core, in and out ab exercises also engage multiple muscle groups, leading to higher calorie burn. This can be beneficial for weight management and fat loss when combined with a balanced diet and regular exercise.

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What Do In and Outs Help With?

In and Outs help with the ab muscles in your core. Proper form necessitates lower back strength, while hip flexors enable 'in' and 'out' movement.

What Muscles Are Used in the In and Out?

The muscles used in the In and Out movement are the abdominal muscles; the rectus abdominis, obliques, and transverse abdominis. Proper form will also activate your hip flexors and lower back muscles.

Can I Do Abs Every Day?

No. You should not do abs every day. Like every other muscle group, the abdominal muscles require time to rest and recuperate after training to recover and rebuild stronger.


  1. https://pubmed.ncbi.nlm.nih.gov/2140344/
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4395661/
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8360586/
  4. https://www.ncbi.nlm.nih.gov/books/NBK531508/
  5. https://www.ncbi.nlm.nih.gov/books/NBK539897/
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About The Author

Senior Coach
Connor Sellers holds a degree in Kinesiology and Exercise Science from Rutgers University He is an author and personal trainer with the mission to inspire people to relentlessly pursue their fitness and lifestyle goals. He mantra is that staying fit has an overall positive effect on one’s body, mind, and spirit.
Learn more about our editorial policy
Dr. Harshi Dhingra, MBBS, MD is a published peer-reviewed author and renowned physician from India with over a decade of experience. With her MBBS from Bharati Vidyapeeth and an MD from Rajiv Gandhi University, she actively ensures the accuracy of online dietary supplement and medical information by reviewing and fact-checking health publications.
Learn more about our editorial policy
Dr. Kristy June Dayanan, BS, MD is an author with a BS degree from University of the Philippines and an MD from University of Perpetual Help System. Her ability to simplify medical science complexities and dietary supplement jargon for the average reader makes her a valued medical fact checker and reviewer.
Learn more about our editorial policy

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