There are four obvious parts of the body that need to get stretched when doing back bending:
The thighs.
The hip flexors.
The upper body.
The shoulders and arms.
(Of course the entire body is involved when practicing asanas but it’s possible to focus on special areas.)
To exercise certain muscles isolated is not so overwhelming like exercising the entire body together. It helps to deepen the understanding of an asana. It’s effective. It’s possible to adjust the exercises to one owns need. Some have flexible arms, others are stiff there. Most people have stiff hip flexors, but there are also people who are very flexible, but lack strength for instance. There are the ambitious and the talented. It’s good advice to individualise the training.
In the above picture I stretched my legs. I pushed the feet into the ground to push the upper body towards the head. This is a relative easy stretch. This exercise gives the body the opportunity to get used to this sort of stretching. The hands support the back and the movement.
More challenging asanas will come.
I usually integrate exercises in my morning practice.
Stretching takes time and patience. Every injury means a set back. Consistency is the key.