A super easy core exercise.
Lying on back, one leg up, lower this leg side to side, controlling the movement with the core.
Hold plank position to form failure.
From lying prone, keep the legs on the ground, while slowly elevating the upper body working the back extensors.
From lying with knees bent, gradually lift the back and hips off the floor to form the bridge position.
From lying on back with legs elevated, crunch and lift to elevate hips off the ground.