Atkins suggests doing 8 to 10 full circles every morning (or before your workout) with each arm to improve your shoulder mobility.

But if you find yourself unable to work through the full range of motion, you're not out of luck. "If you find this exercise challenging, try decreasing the beginning angle (when the arm is overhead, bicep near the ear) by taking the arm a little bit further away from the head," Atkins suggests. "You can also do this exercise standing next to a wall (ball side to the wall), and as your mobility improves, eventually relocate to the ground."

GST Insider Ep 31 Prone weighted arm circle
https://www.youtube.com/watch?v=0cDJsaLMlDE