The pictures shows a shoulder stretch that one can exercise anytime. Whenever the thoughts go to the shoulders one can do this stretch. For back bending strong and flexible shoulders are needed.

When I exercise urdhva dhanurasana the most discomfort is felt around the shoulders and the upper body. To shift the weight towards the feet is not the solution. Stretched the upper body and shoulders is the solution for a balanced bow. When the shoulders and upper body is stretched and strong it’s possible to shift the weight away from the feet towards the hands. Then the bow becomes even.