If you’re a fan of working out, your instructor has probably cued “engage your core!” enough times for it to be drilled into your head.

Trust me when I say, they mean well.

The core is consequential to all movement. Whether you’re only standing upright or throwing a javelin, you need to recruit your core to keep you stable and mobile.

Unfortunately, not all instructors will explain exactly how you should engage the core. In the fitness world, the two most popular techniques are hollowing and bracing.

So to guide you, we’ll discuss both approaches, explain why we advocate for the former, and teach you exactly how to hollow your abs. Let’s dive in!

The Anatomy of the Core

The “core” is often interchanged with “abs” by most people. But in actuality, the abdominal muscles are only one component of the core. Also called the lumbopelvic-hip complex, the core spans from

• the diaphragm at the top,
• the oblique muscles at the sides,
• the paraspinal and gluteal muscles at the back, to
• the pelvic floor at the bottom.

This complex is an integrated unit comprised of bones, ligaments, fascia, tendons, and muscles. The bones and ligaments provide passive stiffness to the core. Meanwhile, the muscles, tendons, and fascia supply active stiffness through contraction.

Both active and passive units are monitored and controlled by neural and sensory elements. Their main goal is core stabilization, which, as we’ll explain later on, is crucial for health and performance.

Muscle groups in the core can be categorized into two systems: local and global. The local group is composed of deeper abdominal muscles dubbed as ‘stabilizers’. They maintain posture and support the spine. Key local muscles include the:

• transversus abdominis (the deepest muscle also known as “the corset” for wrapping around the midline),
• multifidus (thin strips of tissue filling the crevices between the transverse abs and the bony projections of the vertebrae),
• internal obliques (a pair of muscles on the side body running diagonally from the bottom of the ribs and the top of the hips), and
• pelvic floor muscles (muscles lining the bottom of the core that hold pelvic organs in place and assist in bodily functions around that area).

Meanwhile, global abdominal muscles are larger muscles found on the surface. Because of their size, they can produce powerful torque and movement. Here are some of the key muscles in this system:

• erector spinae (a muscle group running along the back of the spine, allowing it to stretch, rotate, and flex),
• external obliques (large superficial muscles on the side body that aid trunk rotation and flexion), and
• rectus abdominis (more commonly known as the 6-pack muscles, which help with trunk flexion).

These muscles are protected, connected, and held in place by fascia, connective tissues surrounding every cell in our body. In addition to these functions, the fascia also transmits load between the muscles.

One of the most important fasciae in the core is the linea alba. It is a fibrous tissue running down the midline of the abdomen. Because it anchors many of the key local and global muscles, it plays a crucial role in the stability of the abdominal wall.

Among the muscles connected to the linea alba are the pyramidalis. When this pair of muscles contracts, the linea alba tenses. This process prevents weakness and overstretching that lead to instability, pain, and poor posture. The pyramidalis is also richly innervated and contributes to neurological control in the core.

The Importance of Core Stability

As mentioned, all the parts of the core work together to provide stability. Here’s why it’s so consequential to our health and athleticism:

Improved Balance and Posture

Proper activation of the abdominal muscles helps with neuromuscular control and alignment. This engagement positively affects balance and posture.

Various studies have shown that core stabilization improves static and dynamic balance and self-perceived confidence to balance. This effect has been seen amongst different populations, from Parkinson’s patients and older adults to athletes.

Optimized Sports Performance

A stable core allows the effective transfer of force and energy from the trunk to the limbs, and from the lower limbs to the upper limbs. This smooth transfer is crucial for powerful and efficient movement in sports.

Swinging a racket, for example, requires the pelvis to initiate movement and transfer energy to the shoulders and arms. Without core stability, much momentum would be lost along the kinetic chains before it reaches the upper body.

Athletes with an unstable core tend to compensate for the lack of power by overusing other body parts. Doing so puts strain on the joints and muscles and leads to injury. Thus, athletes’ need for a strong and stable core cannot be overstated.

Pain and Disorder Prevention

Core stability is key not only for spinal stability but also for spinal health. When our core cannot support our spine, micro-movements happen in the joints that result in degeneration. Pain is a usual consequence of this deterioration but disability can also occur in serious cases.

Moreover, impaired core muscle control hampers the even distribution of load. This is often the cause of low back pain and other back disorders such as osteoarthritis.

Abdominal Hollowing vs. Bracing

So, what is the best way to achieve core stabilization through abdominal muscle engagement? Let’s take a look at bracing first before we explain why we vouch for hollowing.

The Case for Abdominal Bracing

Bracing involves the contraction of all abdominal muscles to stiffen the lower trunk. Proponents of this technique argue that it is more effective because it engages more muscles in the core.

Indeed, various studies using electromyography (EMG) and magnetic resonance imaging (MRI) have found bracing to engage more muscles than hollowing. Literature on the topic also confirms that compared to hollowing, bracing is better able to increase intraabdominal pressure (IAP) which enhances spinal stability.

The Case Against Abdominal Bracing

However, these advantages come with trade-offs. Higher levels of muscle recruitment produce signal-dependent noise (SDN). This noise perturbs the spine and degrades postural control. Bracing also comes at the cost of increasing spinal compression, which can lead to injury and illness in the long term.

Furthermore, the elevation in IAP from bracing carries some risk for individuals, especially women, as it overloads the pelvic floor. Some experts also believe that constant contraction of the abdominal wall hampers our body’s natural ability to regulate IAP.

Why We Recommend Abdominal Hollowing Instead

Hollowing recruits the local muscles and minimizes the activity of global muscles. Thus, the maneuver is still able to provide stability to the spine without unsettling it with SDN.

For the same reason, hollowing is better suited for dynamic stability. As you may remember, the main responsibility of local muscles is to stabilize the core, while the global muscles produce and control movement. Bracing contracts all these muscles, which can hamper movement and torque.

Finally, proper hollowing lengthens the spine instead of compressing its discs. A tall spine is a prerequisite for nerve health, proper posture, and core stability.

To be clear, bracing has its place in daily life and sports. In situations where you need to protect your trunk from a heavy blow, bracing makes the most sense. Boxing and other contact sports come to mind. Bracing also applies well to sports such as weightlifting.

How to Hollow Your Abs

The practice of hollowing your abs in Rev6 is quite different from the usual. Most practitioners will instruct you to draw the belly button to the spine.

Here at Rev6, we teach students to draw the area between the belly button and the pubic bone towards the spine. This contraction activates the pyramidalis muscles, which anchor our abdominal fascia and muscles.

When hollowing, feel your lower abs contract at a slight angle towards the last vertebra of your spine. If you do it correctly, you’ll notice that your torso lifts automatically. If you feel yourself hunching over while hollowing, it’s most likely because you are trying to hollow from the belly button.

An important tip to keep in mind while hollowing is to breathe as normal. Remember, the diaphragm is part of your core! A disrupted breathing pattern has been shown to hamper the performance of the maneuver.

Make sure to watch our essentials video to get more guidance on hollowing your abs, alongside the 5 other essentials of Rev6! And if you want to practice exercises that encourage the hollowing of your abs, make sure to follow up with our free foundation class.