It's based on the theory that like animals we keep trauma in the body. Have you ever seen a dog or cat after being run over or hit by a car? Well they shake uncontrollably and release the trauma then they get up and they are fine again. I think it's different for us humans though. It's not that easy but it makes sense that the initial trauma is released the shock and perhaps this is where the two therapies are good together to release the body trauma and talk therapy for the memories and feelings! Peter Levine book waking the tiger is pretty good at explaining the science behind it all.