I love this gentle lead into the deeper backbends and tend to include it along with pretty much all the Bow sequence when practicing backbends. Much of Bow is similar to the backbend section of Ashtanga Intermediate series but with more vinyasas, more time spent preparing for the deeper backbends.
I often add and/or mix the Bow Subroutine with/to the Meditative subroutines, which includes the Kapotasanas.
Most if not all of these postures and/or subroutines can be used as counterposes for Shoulderstand and/or any deep forward bend although you would tend to start with the lighter vinyasas
These postures tend to be repeated three to six times entering on the inhalation exiting on the exhalation except for manduka asana where you stay in the posture from 3 to six breaths
As with all backbends your aiming to stretch the whole length of your spine
Stretch and lift out of your pelvis just as if you were standing
Stretch and push out the chest on the inhalation, stretch the legs on the exhalation bringing them towards your buttocks.
Manduka ( pic 4 ) can put a lot of stress on the knees make sure the muscles from the pelvis to the ankles are activated, the muscles that cross the knee will give support.
In the beginning use the feet just as support for the hands to push down upon and lift the chest and head, later, in time , when you become more confident of your knees and have built strength in your legs look to push your feet closer to the mat.
As you push down on your feet stretch out through your thighs which will lift the knee and tilt the feet closer to the mat.
NB: These are practice notes that will be tidied up and put into the new edition of my Vinyasa Yoga Practice Book along with the current sequences and subroutines. The book can be freely downloaded HERE. There is a page on Facebook HERE with all the latest sheets and updates. This book is in no way a substitute for Ramaswami's Complete Book of Vinyasa Yoga.