This move will work both your butt and your lower back — all you need is a floor!
Start on all fours, with your hands directly under your shoulders and your knees directly under your hips.
Keep your right knee at a 90-degree angle as you slowly raise your leg behind you until your thigh is almost parallel to the floor. Pulse your flexed foot toward the ceiling by squeezing your glutes. Your back should remain perfectly still in a neutral spine. The motion should be small and controlled with the muscle doing the work and not momentum.
Return to start position to complete one rep. Do 20 on each side, two to three times.