As Iyengar explains, in Dhanurasana (Bow Pose, 4* on the scale of difficulty), “the hands here are used like a bow-string to pull the head, trunk and legs up.”
In my practice, the hands alone are not the bow-string. The hands, the legs, and the breath are all part of the bow-string. When I rise up into Dhanurasana, I press my ankles into my hands to help reach my legs and chest off the floor. My hands don’t pull my head, trunk, and legs up so much as they help shape the movement of my legs pressing up and away.
Also, Iyengar guides the practitioner to exhale when reaching her legs and torso up into Dhanurasana. I prefer to come into the asana on an inhale, using the expansion of my lungs and chest to lift me higher into the pose. In Dhanurasana, my inhale feels like a gust of wind filling a sail. It gives me the energy and momentum to steer my body further away from the floor.