If you hear “a strong core” and instantly think of sharply defined abs, you’re not alone. “When talking about our ‘core’ we often focus on the parts that we can see or have been told by society that indicate a strong belly—the rectus abdominis, also known as the ‘six-pack’ muscle,” says Kristin Leal, a New York-based yoga teacher and the author of anatomy books including MetaAnatomy: A Modern Yogi’s Practical Guide to the Physical and Energetic Anatomy of Your Amazing Body.

But the truth is your core is a central structure of your body that’s key to your overall health. All of the abdominal muscles—plus the muscles in your back and pelvis—work together to help keep your body stable and balanced. They also protect your spine. Your core is doing a ton of structural work, even if you aren’t wearing washboard abs. The best way to respect the work your abs do every day is use these muscles with care. 

Know your abdominal anatomy

There are four main abdominal muscles, says Richelle Ricard, yoga teacher and author of The Yoga Engineer’s Manual: The Anatomy and Mechanics of a Sustainable Practice.

• Rectus abdominis: A pair of long muscles that run from the sternum to the pubic bone, they allow you to flex forward. The appearance of a “six-pack” or “eight pack” comes from tendinous bands (inscriptions) that cross the muscles.  
• Transversus abdominis: This is your deepest ab muscle, which wraps around the waist to stabilize and support the spine. 
• Obliques: Inner obliques run diagonally up your sides; outer obliques slant down towards your public bone. Muscles that run in opposing directions such as the obliques, work against each other to stabilize your lumbar spine, Ricard says. Both sets help you flex and compress your trunk and bend to the side. Obliques are also rotational muscles that allow you to twist. 

Abs and back are a symbiotic support system

The big rule in anatomy, Leal explains, is that everything is connected.

“Conceptually, we don’t usually think of the abdominals as spinal muscles,” Ricard says. But the transversus abdominis, and internal and external oblique muscles connect to the lumbar spine and fascia. They help stabilize your movement, hold your abdominal organs, and support the curvature of the spine

In whole body movement—including most yoga poses—the entire body has to work in coordination. This is especially true of the abdominals, explains Ariele Foster, a physical therapist and yoga teacher based in Washington D.C.   She is the founder of Yoga Anatomy Academy. 

“Abdominals need to work in conjunction with the diaphragm for respiratory health; with the pelvic floor for stabilization of your hips, as well as bladder control and urinary health; and with the multifidus muscles, which stabilize the lumbar spine to create a stable trunk,” she says. If one of those structures is dysfunctional, or not doing its part, it’s like a group project with lopsided effort, Foster adds.    

Where your abs come into play

An important thing to remember is that your abs are nearly always “on” during typical movement throughout your day—not just when you’re holding Crow Pose or coming into Boat Pose. Your core muscles work together to stabilize the torso, says Foster, whether you’re doing yoga, sitting, squatting, or just walking to the mailbox. We most often think of the core in poses such as Crow, Boat or Plank, but they are also activated in more gentle poses such as Cat and Cow. And Triangle is one pose where all of your abdominals are activated at once. These unlikely poses can help strengthen your abdominals, too. 

Trikonasana doesn’t usually make it on lists of ab-focused asanas. But “all of the abdominal layers are in play here,” Ricard says. “Triangle is a very complex pose when you look at what needs to contract, and where.” 

In this pose you put your spine out sideways, dropping your ribs lower than your hips.  The obliques have to work to maintain balance while you’re bending to the side. They rotate the spine to help your body achieve that broad, open, stacked-rib look and function. “They hold the waist steady, while simultaneously rotating the ribcage perpendicular to the floor,” says Ricard.

For most people, the hips will not open fully in Trikonasana—at least not without pulling the front knee dangerously out of alignment, Ricard says. “So, to have the broad open chest this posture is known for, the thoracic spine needs to twist.” The obliques will assist. 

Meanwhile, the transverse abdominis and the rectus abdominis help to maintain a neutral spine she says. The upper fibers of the rectus abdominis contract to keep the front ribs pulled down toward the navel, while the lower fibers contract to help the transverse abdominis compress the lower abdomen, and provide resistance to the lumbar muscles. 

There can be a tendency in this pose to pour weight into your bottom arm as you rest your hand on your shin or a block. Instead, Leal suggests first reaching your bottom arm out toward the front of your mat. This forces your obliques to work antagonistically—one engages and one stretches—to create length in your waist. Once you have this feeling, then bring your hand down lightly to your shin or a block for balance. To reverse the pose, use your obliques to pull yourself back up to standing.