The Inner Spiral of the wrist vs the Outer Spiral of the Shoulder
When students first begin to practice Downward Facing Dog, one of two common misalignments typically occurs in the upper body:
As teachers, most of us probably spend a lot of time telling students to ground the inner heels of their hands and an equal amount of time telling them to work the external rotation of their arms at the shoulder joints, while performing corresponding hands-on assists that encourage these actions. These cues will help for awhile, but over time there is the potential that many students will take the "externally rotate the shoulders" cue too far, causing biomechanical stress/torque at the shoulder, elbow and wrist joints.
In the following video...