ZED #22 - Zejax Flag to Arrowhead Side Plank Transition
Assume a flag position, flex the elbow of the arm on top transitioning slowly to the arrow head position until both arms are extended. Observe how the top arm is moving, the bottom arm stays always straight. Feel free to play around and find variations and other transitions.
You can adjust the hands and feet position to make it harder or easier, you don't have to do it exactly as demonstrated on the video.