The back does not really bend— it actually extends! In some schools of Yoga it is called "back extension".
I strongly recommend working on your core muscles before attempting to practice arm balances. This is what I'd tell my younger self if I had a chance!
I.e, hanumanasana or popularly called the splits, would require strong activated core, warm glutes and of course, warm hamstrings. Just diving into the pose might be faster, but it defeats the most important part of Yoga: mindfulness.
Everything begins in the mind. If you want to see clearly, you need clear vision. -- Sri Swami Satchidananda