Reverse plank with knees extended ("Plank, reverse (low)" Core/scapular strengthening isometric)

Lie on your back with your knees extended, your chin tucked in and your weight supported on both forearms.
Push your pelvis upwards, until your thighs are in line with your spine.
Hold this position shortly and lower yourself to the floor.
Do not allow your lower back to arch and keep your pelvis level.
Move up and down in a slow and controlled movement.
Relax and repeat.