I try to keep the three locks/bhandas, (Mula -root, uddiyana-belly and jalendhara-throat ) engaged throughout my practice, in some poses more engaged than others. Uddiyana bandha, drawing in the belly, is especially useful for backbends, seems to help protect the back and ground you somehow, makes you a little more stable.
Recently, somebody mentioned a tip from a workshop where they were told to imagine they had a pea beneath their belly that they were trying not to squish as they were laying in the Salabhasana's (trying to find the source of this anyone remember?). great tip, it really helps but what about standing backbends and kapo, here's my variation.....
This only works if your belly button is an innie, sorry outie's your backbends are just going to have to suffer or perhaps you can come up with your own version in which case please let me know.
The yogi and the pea
So the idea is that you imagine your holding a pea inside your belly button. Now you want to grip that pea so suck your belly in and up, grip the pea and draw it back nice and safe, now keep that engaged like that through your drop back's, kapo's and what have you.
In the video below I'm whizzing through the Bow sequence and part of the meditative sequence. The idea here, as with the previous Leg behind head post, is to show how the postures of the sequences build upon each other preparing you for the more challenging poses.
I'd already done my bow sequence practice this morning, here I'm going in and out of each pose on the breath but earlier, of course, I was repeating the postures three times and or staying in the pose for a number of long, slow breaths.
Key to ushtrasana and kapotasana are getting the hips as far forward as possible, lifting up out of the hips as we do every day in tadasana. There's a tendency to collapse the hips backwards as we go over but all the way keep thinking "hips forward, hips forward...". Mine collapse here because this is my first time doing kapo with my feet and knees together. You may find it easier to work toward the feet together version by practicing with your feet and knees apart.
The full kapotasana doesn't show up in Ramaswami's Complete book of vinyasa yoga but it's there in his earlier book ( and one of THE best books on yoga I've come across) Yoga for the three stages of life.