How the teres major can make or break healthy shoulder in inversions.

In every inversion, from Adho Mukha Svanasana (Downward-Facing Dog Pose) to Salamba Sirsasana (Supported Headstand), you are basically asking your arms and shoulders to act like legs. But there’s a difference: Your legs are well-designed for pushing, resisting gravity, and constantly bearing the weight of your body as it navigates through all types of terrain. Your shoulders, in contrast, are built for pulling and hanging. All the objects that are dear to us—tools, food, loved ones—are held by our hands and carried by our hearts through our shoulders.

When you invert in asana class, you turn that relationship upside down. And doing so safely requires both precision and adaptability. When you ask your very mobile shoulder assemblies to accept the compression of your body’s weight and act like stable legs, then your bone placement, ligament resilience, and muscle balance all play a role in successful, injury-free inversions.

Key to muscle balance in the shoulders is the teres major. (When we refer to any particular muscle, we mean all of its fascial connections and mechanical influences in its area of the body.) So let’s explore the teres major’s entire “zip code.”

To find teres major, reach across and grab the flesh that forms the back of your armpit, with your thumb in your armpit and your fingertips on the outside edge of your shoulder blade. If you slide your thumb back and forth, you can feel the dense and slippery tendon of your latissimus dorsi (or lat) muscle. You can follow it as it curves up around into the humerus (upper arm bone). The lat comes from your lower back, connecting into the fascia of your thoracic and lumbar spine, hip, and even your outer ribs, and eventually winding into a flat, wide tendon that attaches to your upper arm.

Under your fingertips is your lat’s good friend, and our focus: teres major (meaning “big round” in Latin)—a much shorter, square muscle that runs from the bottom corner of your shoulder blade and joins into the humerus right beside, and parallel to, the lat.

What you are holding when you hold the back of your armpit is the control panel for the proper positioning of your shoulder in inversions. The lats and teres major form part of the big X across your back that I call the Back Functional Line. This myofascial (muscular plus fascial) line connects from the end of the lat on your arm, all the way across your back, to your opposite hip and leg.

Isn`t it wonderful how connected our body`s are?