Read the following article and answer the question.

Since four out of five of people have back pain , often lower back pain , sometime in their life , we should know what causes it and how to avoid it . Causes Of Lower Back Pain As we get older , our bodies tend to lose their muscle elasticity and tone , as well as bone strength . The discs in our spine lose fluid and flexibility , and they ca n't cushion the vertebrae as well anymore .

What type of pain or injury is the narrator discussing .
None of the above choices .