For the extension of the spine and to get those underactive upper and mid back muscles working, try a Baby Cobra.

Lie face down on the mat with the arms out to the sides and the legs a little wider than hip width. Try to relax the shoulders. You can place a cushion under your lower abdomen to help ease the work in the lower back. Feel the support of the deep abdominal muscles throughout.

As you breathe out Initiate the movement with a small head tilt and then sequentially peel the top of the spine away from the mat, focus on reaching forward with the breastbone and maintaining length at the back of the neck and in the lower back. Keep the movement small. Breathe in to hold and then return to the mat on the outbreath. Repeat up to 8 times.