With my students, I lunge them at the trot without the reins. At first they can hold onto the mane, but not the saddle as it tends to make them lean forward. This exercise helps them to gain balance and confidence. Eventually, when they are ready and comfortable, they let go of the saddle and put their arms out to the side and above their head, etc. Holding the reins can be a crutch in some ways. This also helps with their legs and seat. We do sitting trot and half seat as well. They love it. Try it out.