A research study (on healthy individuals, with no back pain) showed that bridging exercises, such as the supported bridge pose in yoga, put the oblique abdominal muscles to work to remedy non-neutral pelvic positions. The obliques establish a centered alignment of the pelvis and low back. This has significance when considering the that the bridge pose is the first pose to take the pelvis into space, with no direct support. (The supported bridge pose mediates the transition from having the pelvis on the floor and lifting it in the air, by means of the block under the sacrum.) The study on ab and back muscles also shows that the abdominal muscles are capable of fine control over pelvic and low back movements.
1 Stevens VK, Bouche KG, Mahieu NN, Coorevits PL, Vanderstraeten GG, Danneels, LA.Trunk muscle activity in healthy subjects during bridging stabilization exercises BMC Musculoskeletal Disor Sept 20 2006