How, specifically, does being overweight affect your back and joints?
Eric Robertson, P.T., D.P.T., Assistant Professor, Physical Therapy, Texas State University, San Marcos, Texas, a spokesperson for the American Physical Therapy Association
There are two basic ways that extra pounds can cause an increase in back pain. First, extra weight shifts the body's center of gravity, which may alter posture and mechanically create more strain on the load-bearing joints in the spine, such as the facet joints and disks. Also, some studies have also reported that a stiff thoracic spine is a feature commonly seen in obese people, and this may have something to do with predisposing people to experience chronic low-back pain.
The second theory is that changes in systemic inflammation associated with obesity may make people more likely to experience pain. Obesity is linked to low levels of systemic inflammation, (as compared to normal-weight individuals who do not have this sustained inflammation) and this is thought to be one reason for the increased prevalence of osteoarthritis, periodontal disease and cardiovascular diseases associated with obesity. Obesity and inflammation are thought to be linked through the ability of fat cells to release cellular cytokines, a type of chemical messenger that may increase the body's inflammatory response. These cytokines (in those who are overweight or obese) can also trigger the release of chemicals involved in the transmission of pain, such as Substance P (a neurotransmitter related to pain).
Therefore, people who are overweight may not only have increased stress on their joints but may also be more likely to feel pain.
Nathaniel Tindel, M.D., New York City back surgeon and author of I've Got Your Back (NAL Trade, 2007)
Whether we are talking about the back or any of the joints in the body, what we are really referring to is the cartilage and the synovial lining of these joints. Cartilage makes for a smooth, frictionless surface that allows us to move with ease. If the cartilage is damaged (due to added stress from extra pounds), the joint surface is no longer smooth and frictionless, and this results in pain. The unfortunate fact is that once cartilage is damaged it cannot grow back.