The cat and camel
This exercise is an excellent one to loosen up the lower back. Many people do this the first thing in the morning. It helps set the tone for the rest of the day.
This is not a stretching exercise.
They are fluid movements from one position to the other. Gradually and smoothly, raise your back as high as you can and then lower it back down as far as it will go into a swayback position.
It is also not a fast-moving motion, simply go at the pace that feels the best for you. It should not hurt, not even a twinge of discomfort should be present while doing this exercise.
Start with one set of eight to ten movements and gradually progress up to fifteen to twenty.
In this GIF, she is showing the possible range of motion, correctly done for this exercise. Keep your body centered over your arms and legs for the best results.