My research has shown that this is the gentlest way to mobilize the back since body weight is essentially removed and that will go a long way toward reducing stiffness, and maintaining and improving muscle tone.
How to do a Cat and Camel exercise:
Get down on your hands and knees on the floor.
Relax your head, and allow it to droop.
Round your back up toward the ceiling until you feel a nice stretch in your upper, middle, and lower back.
Hold this stretch for as long as it feels comfortable, or about 15 to 30 seconds.
Repeat this until you feel your back loosen up. This exercise can be be repeated multiple times a day.