I don't see it as a lack of trust. On the contrary it is a deep, intimate and very personal connection between us. It heightens my sense of longing and desire towards my partner, and we use it as a tool to channel my energy in an appropriate direction. In many ways it is similar to yin yoga, where one has to ride the waves of discomfort and give in to a physically challenging situation. It helps me to strengthen my mind and my mental resilience.
On the other side of the coin, I enjoy locking my partner up... I like that it ensures compliance and I enjoy the sense of control I get from the helplessness of their situation. Trust doesn't come into it. Or rather, we have a deep sense of trust to begin with. If it's the base of the relationship it will heighten the experience for both of you. If trust is an issue then it's a recipe for disaster.