If the goal is to have extension distributed throughout the whole spine, there will need to be more action in the thoracic region and less in the lumbar and cervical regions. This translates into concentric work for the extensors in the thoracic spine and eccentric work for the flexors in the cervical and lumbar spines.

The latissimus dorsi are not so helpful in this pose, because they can fix the scapulae on the rib cage and inhibit extension in the thoracic spine. They also produce internal rotation of the humerus and downward rotation of the scapulae, which oppose the actions of upward-facing dog.

Depending on where restrictions are, the humerus can be pulled into either internal or external rotation. Sometimes the external rotation that is active in downward-facing dog needs to be modulated coming into upward-facing dog, because the whole hand-scapula relationship shifts relative to the spine.