Whether you work out your abdominal muscles and/or lower back, it is good to do both of these stretches.
Abdominal muscles: Lie down or stand up and simply stretch your arms and legs in opposite direction. Hold for ten seconds. Repeat at least three times.
Lower back: Lie down and hug your knees. Hold for ten seconds. Repeat at least three times.
Disclaimer: None of the above information can be taken as a substitute for advice from a medical professional such as a physician.
My third book, Pocket Guide to Fitness, is available on www.louizapatsis.com, http://www.authorhouse.com, www.bn.com and http://www.amazon.com. If you look up my name on those Web sites, you will find my other books The Boy in a Wheelchair and Life, Work and Play: Poems and Short Stories.