Awe! Isn't he cute...
In the army, this is known as "Prone Roll Position, DOWN!" as how your Platoon Sergeant will yell at you. It's also sometimes called "Superman". Nobody likes it except maybe the Platoon Sergeant giving the command.
On the internet, this is known as "Prone Cobra", just in case you want to search for it.
How to do it?
Lie face-down, arms by your sides, palms down. Contract the muscles in your glutes (these are you bum muscles above your tighs) and lower back to raise your torso and legs off the floor. At the same time, rotate your arms back till your thumbs point towards the ceiling (the cute baby above is doing it wrong). Hold this position for 60 seconds and rest for another 60. Do 3 sets.
Here are some pictures to help you visualize...
