Shoulders, arms, spine (extension).
From all 4, stretch your arms out in front of you, with arms bent or straight. A good option is using a bolster or pillows under your elbows. Walk your knees back, so you can drop your heart against the floor.
There´s not one way to do this pose. Feel the target area, and modify the pose until you feel the target area, and can allow your muscles to relax.
Stay around 2-3 minutes. Then slowly ease out of the pose and relax on your belly or Child´s pose.