When you lunge forward and back during this exercise, you’re using ground reaction through your feet to drive energy through the body. The moment of the lunge and the throw creates another load diagonally through the core. You’re also activating all the core muscles in your hips, ribs and pelvis.
The motion of the overhead press dives the core to move in three dimensions. By driving the dumbbells sided to side, you also create a top-down force that causes the rib cage and pelvis to move, switching on all the muscles that connect the pelvis, rib cage and thoracic spine.
The posterior lunge and press creates greater hip extension while working the core muscles through three planes, which translates to more flexibility and power.