Crunch Exercise to Build Lean Muscle in Your Abs

Crunch Exercise

Crunch exercise is one of the best exercises to build your abs and strengthen your core. It is a great bodyweight exercise that should be part of any overall fitness plan.

But there are a few things to look out for when performing crunches. They can do more harm than good if a few of these common mistakes are made.

And one of the great things about crunch exercise, is that they can be done just about anywhere with a comfortable floor, or if you have a workout mat. You can get a really killer workout in a matter of minutes, and you only need to do the exercise a few times a week.

Table of Contents

Muscles Worked

Primary Muscles Worked 💪

  • Rectus Abdominis (Abs)
  • Transverse Abdominis

Secondary Muscles Worked 💪

  • Obliques
  • Hip Flexors

Benefits of Crunch Exercise

There are many benefits to doing this exercise as part of your normal fitness plan:

  • Build and strengthen your abdominal muscles
  • Strengthen your core
  • Improve your lower back health
  • Prevent lower back injury

If you are 35 and older, it is important to be aware of your lower back health. You have to be cautious and aware to avoid lower back injuries, and make sure you’re proactive with exercises to strengthen and protect your lower back.

We also like bicycle crunches also for needed variation, and click to learn the benefits of bicycles crunches. Here’s a hint…think obliques. 

Orthopedics generally advise that one of the best exercises to strengthen your core, as well as your lower back, is to perform crunch exercises on a routine basis. This will strengthen your stomach muscles, as well as your lower back muscles. (1)

Click here for additional ways to avoid lower back injury.

As a general rule, you will need to be around 10% body fat to really see definition in the abs. So to see your 6-pack really shine, the heavy lifting is done in the kitchen, not the gym. You need to be on a clean diet plan, and watching your calories and portion sizes. Click to check your body fat percentage.

But you don’t need to be at 10% body fat to have a great looking core and midsection. You can be very lean at 15% to 18% body fat, and look great at the beach, in the office, or at your local happy hour. These crunch exercises will help you to achieve that goal.

Performing Crunch Exercise

Crunch ExerciseCrunch exercise is a simple movement, but yet very effective.

  1. Lie on your back with your knees bent and your feet on the ground. Make sure your upper legs (thighs) are nearly vertical. Place your hands behind your head. This is the start position.
  2. Contract your abdominal muscles as you curl your spine into the crunch position. Your back will arch, unlike a sit-up where it remains straight.
  3. Breathe out as you perform the crunch, and really feel the contraction and tightness in your abs.
  4. Breathe out as your return to the start position.

IMPORTANT NOTE: You want to make sure that you never “pull” with your hands on the back of your head. This can be damaging to your neck and spine if done forcefully.

So make sure that your hands are only there for positioning, and not to help with the crunch movement. You want your abs and core to do 100% of the work, not your arms and neck muscles.

To make sure you are only activating your core and abs, you can also place your arms in a crossed position over your chest (as shown in video below).

Crunch Exercise

Reverse Crunch Exercise (Frog Kicks)

This exercise is another good exercise to work your abs, and is just a crunch in reverse. They are also referred to as frog kicks.

  1. Lie on your back with your legs extended and your arms on ground by your side, with your hands tucked under your rear. Keeping your legs straight, lift your feet 6″ off the ground. This is the start position.
  2. Lift your legs and bend your knees until yours knees are over your stomach area. Breathe out during this motion.
  3. Extend your legs returning to the start position, maintaining your feet 6″ off the ground. Breathe in during this motion.

Flutter Kicks (Scissors)

Flutter Kicks

Flutter kicks (or Scissors) are a variation of the crunch movement, and also target the abs. Flutter kicks are an exercise favorite in the U.S. Military. When I was in U.S. Army Ranger School back in the 90’s, flutter kicks were a form of mild torture 🙂. 

If you could not keep up during PT (physical training), then you went to the back of the formation for one-on-one training with a Ranger Instructor (RI). The weapon of choice was usually flutter kicks. I was one of those guys a few times, and those RI’s were merciless! Good times!

Flutter KicksThe start position is the same as doing the reverse crunch.

  1. Lie on your back with your legs extended. Extend your arms down your sides and tuck your hands under your butt to provide stability and support. Keeping your legs straight, lift your feet 6″ off the ground. This is the start position.
  2. To perform the exercise, alternate moving your legs in an up and down motion with a range of approximately 12″ for each leg. Use a 3-count method of counting – 1-2-3-1, 1-2-3-2, 1-2-3-3, 1-2-3-4 etc.

Ab Workout Routine

A great ab workout is to use a lot of bi-sets and tri-sets with these abdominal muscle exercises. A bi-set is where you perform one set of an exercise, and then immediately follow it with another set of a different exercise with no rest in between the sets.

A tri-set is when you perform three different exercises without rest in between. It will generally be a smoker and your abs will definitely feel it. You can also click to learn about the power of superset workouts.

Bi-Set Ab Workout

  • 30 Crunches
  • 20 Reverse Crunches (Frog Kicks)
  1. Perform 30 Crunches, followed immediately by 20 Reverse Crunches. This is one bi-set.
  2. Perform (3) complete bi-sets with crunches and frog kicks.
  3. Rest 30 seconds between bi-sets.

Tri-Set Ab Workout

  • 30 Crunches
  • 15 Reverse Crunches (Frog Kicks)
  • 10 3-count Flutter Kicks
  1. Perform 30 Crunches, followed immediately by 15 Reverse Crunches, followed by 10 3-count Flutter Kicks. This is one tri-set.
  2. Perform (2) complete tri-sets.
  3. Rest 1 minute between tri-sets.

Crunch Exercise

Lastly, it’s a great idea to do hyperextensions at the end of your workouts to maintain a focus on your lower back health.

A good lower back stretch at the end of your workout is one of the best ways to prevent lower back injury, and to keep your back healthy.

Keep your back active and supple and your back will remain strong and healthy. Let it go stale and inactive, and you’ll suffer from lower back pain, or even worse, incur an injury.

Click to see more exercises for ripped abs.

David Williams

David Williams

A diet and fitness enthusiast, David is an ex-Army Airborne Ranger and Infantry soldier with decades of fitness and wellness experience. A West Point graduate with a degree in engineering, he focuses on technical research related to fitness, nutrition, and wellness. He loves the beach and working out, and spending time with his wife and daughters.

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  1. WebMD. (n.d.). Exercises that can help ease back pain. WebMD.

Click to see our medical disclosure.