1. Up-and-Down Arch: While on your hands and knees, let your low back relax down as far as you comfortably can (like a sway-back horse). At the same time lift your head up and back as far as you comfortably can. Hold for a 3 to 5 count then arch your back up (like an angry cat) as you lower your head. Hold for a 3 to 5 count. Repeat up to 8 times.
2. This next exercise not only improves full spine mobility it also improves coordination, especially in people who never crawled or crawled very little as an infant.
Cross-Crawl: While on your hands and knees on a carpeted area, move one hand and the opposite knee forward as you turn your head towards the side of the hand moving forward. Continue moving forward with the other hand and opposite knee. Go slowly as you reach (and turn your head) as far as you comfortably can with each "step." Crawl down and back on your carpeted area several times depending on how far you have available.