By Julie Gudmestad
Published in Yoga Journal

Are your students really ready to invert? Help them condition the muscles that support the shoulder blades to build safe, stable inversions.

How do you decide when to start teaching your students inversions? In particular, when do you start teaching them Sirsasana (Headstand)? The "king of poses" certainly has many benefits, but it admittedly has a few risks, too. You'll want to consider your students' postural alignment, any medical conditions, and upper body strength and endurance before you introduce the pose in class.

An important component of upper body strength for inversions is the group of muscles that support the scapula (shoulder blade). After all, the socket of the shoulder joint is part of the scapula, and the scapula forms the connection of the arm to the torso. As you move your arm into various positions, or bear weight on it, the scapula must be positioned just so, and the shoulder girdle (as the muscles that support the scapula are called) must have the strength to support and hold each position.

For example, shoulder flexion (bringing your arm forward and up next to your ear) must be accompanied by upward rotation of the scapula. Ask if you can watch a shirtless friend, from the back, raise his arms up overhead. You'll see that each scapula moves away from the spine and rotates up so that the shoulder socket, on the outer edge of the scapula, faces up. The scapula's inferior angle (bottom tip) moves all the way out to the side of the ribs as it rotates, and the medial (inner) border, which usually lies parallel to the spine, angles away from the spine. The relationship between upward rotation of the scapula and shoulder flexion is so strong that it's a kinesiological law. If your student lacks strength in the upward rotators, shoulder flexion will be limited in range of motion or endurance—or both.

For inversions in which the shoulders are flexed, including Sirsasana, Pincha Mayurasana (Feathered Peacock Pose), and Adho Mukha Vrksasana (Handstand), the scapulae must rotate upward, and the muscles that support the scapulae must be strong. In the case of Adho Mukha Vrksasana, the weight of virtually the entire body is borne on the hands and arms.

An Unknown Muscle

So what are these all-important muscles? The prime mover for upward rotation is the serratus anterior. To many yoga students and teachers, it's a nearly unknown muscle—which is unfortunate given its essential function in inversions. Part of its obscurity may be due to the fact that it's difficult to locate, see, or feel.

The serratus anterior attaches to the outer sides of the upper eight ribs, and these attachments appear to form a serrated edge that you may be able to see on a lean man practicing Sirsasana. The muscle fibers then extend backward, between the ribs and each of the scapula, to attach to the underside of the scapula at the medial border. When it contracts, the serratus pulls the scapula forward, away from the spine. The angle of the muscle fibers pulls the inferior angle forward faster, causing upward rotation. After the first 30 degrees of shoulder flexion, this rotation happens at the precise ratio of one degree of scapular rotation for every two degrees of shoulder flexion, which is called the scapulo-humeral rhythm (the head of the humerus is the ball that fits into the scapula's socket to form the shoulder joint).

If your student starts taking yoga without a recent history of bearing weight on her arms—not uncommon in our society—the serratus is likely to be weak. Attempting inversions with a weak serratus is a prescription for a collapsed pose: the muscle isn't strong enough to hold the scapula in upward rotation, which means she'll lack the push through the arms that lifts the pose up out of gravity's pull. She'll be unable to get her head off the floor in Pincha Mayurasana, will have trouble getting up and staying up in Adho Mukha Vrksasana, and will likely suffer neck compression in Sirsasana. Since these are frustrating problems that may cause injuries, teachers should take plenty of time to strengthen the serratus before teaching inversions that involve shoulder flexion.

Toning the Serratus Anterior

You can begin working the serratus with even your most deconditioned students by having them start on hands and knees. In that position, when the ribcage drops toward the floor and the scapulae move toward the spine, causing a "valley" to form between them, the serratus is stretched and not contracting.

Instead, have your students lift the torso up away from the floor, opening and broadening between the shoulder blades—but not so much that they flex the spine up like a cat's back. When they've gotten the feel of this serratus contraction, have them lift their knees up into Plank Pose (the "up" position in a push-up), which puts a bigger load on the serratus, without letting a valley form between the blades.
The serratus can be further conditioned in Adho Mukha Svanasana (Downward Dog) by practicing transitions between Dog and Plank, and also in push-ups (weaker students may need to work on push-ups with their knees on the floor initially, and their bodies forming a line from knee to hip to shoulder). Ask your students to hold these positions for increasing periods of time, building isometric strength, which is the same training the muscles need to hold the scapulae in upward rotation in an inversion. The reward for all this hard work will be a strong, stable foundation on which to build a beautiful, light, and spacious inversion.