Lie on your back, and place your hands on the floor for stability. Bend your knees and lift your left leg up toward the ceiling, keeping your knee at a 90-degree angle.
Press your right heel into the floor, and lift your pelvis up into a bridge position.
Slowly lower your body to the floor, making sure to tap your butt on the mat before raising up again. Repeat with the same leg for the full 40 seconds.
Once the 40 seconds is up, rest and complete the move with your left foot planted on the ground.