Built By Science: Abdominals

You can't have a strong, muscular physique without a healthy, stable core. Learn the anatomy and function of your abdominals to achieve your dream physique.

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When people talk about abdominals, the conversation usually doesn't go far beyond the six-pack, but the core actually goes much deeper than any of the visible ab muscles. It's time to learn how and why these muscles matter to the healthy movement and function of your body.

I'm going to teach you which muscles make up your core, what they do, and how they collectively work to stabilize your trunk so you can move heavy weight. Your abdominal training is about to get a serious pick-me-up. Here's how science can help you achieve stronger, healthier abs.

Built By Science Abdominals
Watch the video: 15:56

Muscular Anatomy

Despite popular belief, your abdominals are much deeper and more complicated than that superficial six-pack you check out in the mirror. Let's get to the core of the issue.

Anterior Core

These are the abdominal muscles you'll find on the front of your body. They're comprised of three layers: the deep layer, the intermediate layer, and the superficial layer.

Deep Layer

These three muscles work together to help pressurize your inner-core musculature. Without this pressure, your core couldn't stabilize and allow you to do those heavy deadlifts, squats, or overhead presses.

muscle anatomy
Thoracic Diaphragm

A lot of people don't talk about the diaphragm in terms of exercise, but it's critical to respiration. The diaphragm starts on the front inside of ribcage, comes up and around, and connects to the lower back.

Pelvic Floor

The pelvic floor is made of muscles positioned below your pelvis. When you take a deep breath, your diaphragm comes down, and your pelvic floor catches the breath. The thoracic diaphragm and the pelvic floor pressurize and stabilize your spine.

Transverse Abdominus (TVA)

Your transverse abdominus is layered below your internal obliques and is another significant part of stabilizing your pelvis. It starts on the linea alba—the connective tissue that runs down the center of your torso—and attaches to the lower back.

Intermediate Layer

The internal layer of your core lies between the deep and the superficial layer. It's made up of a few muscles, but the most important is the internal oblique.

Internal Oblique

This muscle runs from linea alba—a vertical line down the middle of your anterior trunk—and attaches to the hip bone. It runs low to high, perpendicular to the external obliques. The internal oblique is an important muscle in respiration and torso rotation.

Superficial Layer

These are the muscles everybody wants to talk about. If you're lean enough, the superficial layer of abdominal muscles forms a visible six-pack.

External Oblique

The external oblique runs from the ribcage down to your hips. Most people think of the external oblique as a trunk flexor or rotator, but it's also a crucial muscle for stability through the core and midsection.

The external oblique helps posteriorly tilt the pelvis. A lot of people have the tendency to fall into anterior pelvic tilt, in which the lower back is arched and the hips are back, which creates a lot of pressure in the lower back. The external oblique is important for pulling the pelvis back to a neutral position.

Rectus Abdominus

The rectus abdominus originates on the pubis and inserts on the fifth, sixth, and seventh ribs, as well as the bottom portion of the sternum. It's separated vertically by the linea alba and horizontally by three or four bands of connective tissue. These separations create six or eight muscle bellies that are collectively called the six-pack.

Your abdominals are much deeper and more complicated than the six-pack in the mirror.
Your abdominals are much deeper and more complicated than the six-pack in the mirror.

Posterior Core

Your core consists of more than just the muscles on the front of your body. It's important to know what's happening on the back. We're going to focus on three specific muscle groups in this section: the multifidus, quadratus lumborum, and erector spinae.


The multifidi are small muscles that span 2-4 segments of the spine. You'll never see them, but they're important because they give your brain feedback about where your body is in space. These muscles also help control little movements throughout your spine.

Quadratus Lumborum (QL)

This big muscle runs from the top of the hip all the way up to your lower back. It's important for side-to-side movements, but it's even more important for preventing side movement. Your QL is necessary for controlling or resisting motion.

Erector Spinae

This muscle group starts at the sacrum and the top of the hip and connects to the ribcage, the top of your neck, and even as high as the base of your skull. These muscles are important for controlling motion during squats and deadlifts. If you need to maintain a little extension, that's where erector spinae come into play.

The erector spinae are important for controlling motion during squats and deadlifts.
The erector spinae are important for controlling motion during squats and deadlifts.

Skeletal Anatomy

We many not think about them as often, but the bones and joints of your abdominal region are just as crucial to your training and development as your muscles.

muscle anatomy


The pelvis has two major motions: anterior tilt, which is rolling the hips forward and popping the hips back, and posterior tilt, which is rolling the pelvis underneath.

Lumbar Spine

Your lumbar spine is comprised of the five vertebrae between your rib cage and your pelvis. It moves in lumbar flexion, or bending over forward; lumbar extension, which is arching backward; lateral flexion, or bending to the side; and rotation, which is rotating your torso to one side or another.

As important as these movements are when it comes to training, resisting motion is just as important. The lumbar spine doesn't move much, other than front to back, so the more you can control or resist motion, the healthier your lumbar will be. A healthy lumbar means bigger, heavier lifts for a longer period of time.

Muscular Function

The following are the exact movements your core is designed to do. A lot of people like talking about big-bang exercise like crunches, sit-ups, and side bends. In reality, your abs do a lot more than just flex. Here are the five motions you should know:

Intrathoracic Pressure

Take a deep breath in and hold it. That's your diaphragm pressing down into your pelvic floor and out into your transverse abdominus. This pressure gives you a strong, stable spine to squat, deadlift, and overhead press.


Most people think your abdominals are only made to flex your trunk. They also control extension through the spine and lower back. Many people struggle to control arching backward. Your rectus abdominus and your internal and external obliques connect to the front of your pelvis and help control your lower back.

Lateral Flexion and Anti-Lateral Flexion.
Lateral Flexion and Anti-Lateral Flexion

Lateral Flexion and Anti-Lateral Flexion

Internal and external obliques help you bend toward one side. This is called lateral flexion. The obliques and the quadratus lumborum are also important for keeping your spine neutral, which is called anti-lateral flexion. Imagine carrying a heavy bag of groceries. You need one side of your body to stay strong to control the motion so the other side doesn't just drop to the side.


The rectus abdominus, transverse abdominus, and internal and external obliques are responsible for keeping your body from rotating too far. Like anti-lateral flexion, anti-rotation helps keep the torso neutral against pressure. To do any push or pull with one side of the body, you need anti-rotation.

Medicine Ball Twist
Medicine Ball Twist


Crunches and sit-ups are examples of flexion. Your ability to bend forward is important, but if you're squatting or deadlifting, you better hope you don't fall over forward. Your core's ability to keep your torso from rounding over is going to keep your spine healthy and allow you to move more weight.

Key Exercises

Now that you understand the anatomy and biomechanics of your abdominals, it's time to put that knowledge in action. It's time to move past endless crunches; here are some key movements that will help you get the most out of your core training.


The TRX fallout is a great exercise because it will help you sculpt that six-pack and create balance. Many of my clients have a tight, stiff lower back. They need some core strength to help offset the tension and build better anterior and posterior balance.

Set up on your toes with your hands under your shoulders, holding onto the TRX straps. Exhale to keep your core tight and hold that position. From here, allow your hands to fall in front of your body. Keep your core tight and your back straight and pull yourself back up.

In the bottom position, you use your rectus abdominus and internal and external obliques to control the motion and force a neutral spine, neck, upper back, and butt.

TRX Fallout
TRX Fallout

EXERCISE 2 Dead Bugs

A lot like the TRX fallout, this movement will help you control and resist extension through your lower back.

Lie on your back and reach your hands toward the ceiling. Bring your feet, knees, and hips up to 90 degrees. Exhale hard to bring your ribcage down and flatten your back to the floor. Hold this position through the set.

From your starting position, extend and push through one heel and then bring it back up to 90 degrees. Your back is going to want to arch. Resist that tendency. Stay tight and reach long through the heel.

EXERCISE 3 Pallof Press

This is a fantastic exercise for teaching your body how to resist and control rotation from side to side.

Grab a D-handle cable attachment and pull it to your chest. Stand up and extend the handle so that your arms are straight. The weight will try to pull you back, but you can resist with your internal and external obliques, transverse abdominus, and QL. These muscles will keep you from rotating toward the weight. Hold the resisting position for 20-30 seconds, and then switch sides.

EXERCISE 4 Suitcase Deadlift

The suitcase deadlift will teach you how to control side-to-side motions through your core and the spine. Pick up a dumbbell from a bench and stand straight up. From this position, shift your weight back through your hips into a single-handed deadlift, and then pop back up. Keep your hips down and your chin down. Progressively work through a greater range of motion.

Because that weight is on one side, you're going to work hard to keep the opposite side stable. So not only is this exercise great for strength, it's also going to train those stability muscles like your obliques and your QL.

Better Abs, Built By Science

At the end of the day, your abdominal muscles are everything to your core. They literally tie your upper and lower body together. Whether you're doing this trainer for a better physique or you want to lift more weight, you need a strong, stable midsection for optimal results.

Ab training is not about moving through your lumbar spine, but it's about being able to resist motion. Understanding this aspect of your core can help you train it more effectively. All in all, this knowledge will help you look and perform better.

Follow the Built By Science Program

Look for the exercises and techniques discussed above in the weekly abs workouts of the six-week Built by Science program. Watch all the overview videos before attacking the gym. Remember, you need to combine mind and muscle to build your best possible body.

Main | Legs | Chest | Back | Shoulders | Arms | Abs | Nutrition | Supplements | Get Started