Lifting the head straight up to look at the heels
In prone position, lying on your front side. You lift your head together with your arm to see your heels, one by one. You use the floor to push yourself up. You hold your foot with your same side hand and explore kinematic linkage by pulling your head up by pulling on your shoulder with your leg.
A classic extensor lesson to improve the organisation of your back to lift your head. There's a strong focus on lifting the head straight up in the sagittal plane, and not to sway left or right. Important learning points include: Do not avoid the directions that seem to be unavailable at first, but instead move slowly, delicately, and within the available range. Use less effort in order to have faster improvement. Do not use force to try to achieve movement learning goals. Soon enough that available range will extend and open up new possibilities.