I would not recommend teaching a larger breed to do this. The trick is to have your dog jump off of you and do a back flip before landing back on the ground.
Hold a treat high up in front of you, and project one leg slightly forward so that your dog will see that as a launch platform.
Pat your chest and give your command. "Backflip" is a good choice.
At first your dog will try to jump straight for the treat. Hopefully your dog will realize pretty quickly that she can jump closer to the treat by using you as a launch pad. Praise your dog and reward her when she figures this out.
The next step is to start drawing the treat away from you so that after launching off of you, she has to arch backward to go for the treat.
Let her get the treat sometimes.
Eventually, you'll be able to have your dog to do a backflip on command.