Can you explain something to me? I work in the purchasing department of a large hospital. My job involves light lifting but constant bending over to pick up items and then putting them on shelves. I notice on Monday and Tuesday, I'm just fine but by Wednesday my low back starts to ache. I can make it through to the weekend. After resting I'm fine again but on Monday, the cycle starts all over. What's happening with my back?

Recent studies show various soft tissues with elasticity have a property called creep. This tells how much tightness or looseness there is in ligaments, discs, joint and capsules. There is also a certain amount of creep in joint capsules.

As tissues shorten from use, they loose elasticity and the creep increases. With repeated work loads or movements, creep doesn't fully recover or return to normal after rest. Over time the amount of creep adds up. If the creep doesn't fully recover from one work day to another, then the workers starts the new workday with too much creep in the tissues.

Creep causes damage to the tissues. The body tries to heal itself and sets up a cycle of inflammation. Continued motion keeps the spine from healing. The added creep results in chronic inflammation and disability.

Scientists are trying to find out just how many repetitions are needed to cause damage and injury to the spine. The goal is to give workers a work-to-rest ratio for safety in the work place.

Paola Sbriccoli, MD, PhD, et al. Static Load Repetition Is a Risk Factor in the Development of Lumbar Cumulative Musculoskeletal Disorder. In Spine. December 1, 2004. Vol. 29. No. 23. Pp. 2643-2653.