The super surfer
(Or some call it the superman exercise)
Perform this exercise 5x each side.
You need a small ball as a measurement tool.
Take a four point kneeling position with your hands below your shoulders and your knees below your hips. Your spine is in a neutral position. You can place a small ball on your lower back. You will lift 1 arm and the opposite leg from the floor and extend it horizontally. Slowly move them back. The ball will not fall off if you kept your spine in the neutral position.
For the experts: if you succeed, then try it without the support on your knees.