Step 1: Begin this movement from a plank position, on the forearms, as opposed to the hands; aligning your shoulders directly above the elbows.
Step 2: While maintaining a solid plank, begin to bring your body forward by pressing down through your forearms, without actually moving your arms. The resulting motion will end up with your shoulders past your elbow level.
Step 3: Once you have reached as far forward as you can, being to press upward through your forearms, resulting in a movement of your body back to the starting position.
Step 4: Repeat this flexion/extension of the shoulders ( ie: pressing down and up through the shoulders) several times.
How to progress the exercise
This explosive movement can be progressed by increasing the height of the hop. Also, pausing on the landing foot after having completed the hop (keeping the knee at chest level) is another layer that can be added to this movement. Incorporating a BOSU under your front will add an additional challenge level.
This movement can be regressed to a more comfortable level by taking away the hop, as well as reducing the drive of the knee. Once you get comfortable with the less explosive version, you can go to the hopping version.