Side plank on knees with hip abduction ("Plank, side (low)" Core/scapular stabilization, abducting straight leg)

Lie on your side and prop yourself up on your elbow.
Bend your knees and lift your hips off the mat until you have a straight line from your knees to the top of your head.
Holding this position, straighten your top leg out, and then lift it directly up towards the ceiling.
Ensure this leg does not travel forwards.
Control the movement as you lower the leg back down and then repeat.