There are several arm positions that may be used for poses.
We may always bring our arms to prayer position when holding poses like Tree, Warrior I and lunges.
We have options of prayer position, hands on shoulders, hands on hips, hands on thighs, on our lower back or just about anywhere that is comfortable for you.
When practicing forward fold, we have options of bringing our arms down through the mid-line of our body or out and around.
Be mindful of “extending the lever” . . . extending arms fully out in front of our body which can put pressure on our lower backs.