Your shoulder blade is the large, flat, triangular bone on your back, just below your shoulder. You have two of them, one on each side of your upper back. If you reach your arm across your body and touch the back of your opposite shoulder, you can feel its edge. When you squeeze your shoulders back, you can feel your shoulder blades move closer together.

The proper medical term is scapula, but most people say shoulder blade because of its flat, blade-like shape. This bone does important work: it connects your arm to your body and helps coordinate all the complex movements your shoulder can make. Your shoulder blades slide and rotate across your back when you reach, throw, or lift something overhead.

Athletes especially rely on strong shoulder blades. A swimmer's shoulder blades shift with every stroke. A gymnast's shoulder blades help stabilize their body during a handstand. Even everyday activities like carrying a backpack or throwing a ball depend on these bones working smoothly. Though you can't see them easily, your shoulder blades are working hard whenever your arms are in motion.