The escalating obesity epidemic in the United States has focused attention on obesity as a risk factor for coronary artery disease, type 2 diabetes, and hypertension. But being overweight is also a risk factor for osteoarthritis (OA), the degeneration of the cartilage at the ends of bones, which results in painful and restricted movement, said an expert at the 55th Annual Meeting of the American College of Sports Medicine.
Stephen P. Messier, Ph.D., FACSM, presented a lecture on The Burden of Obesity: A Biomechanical Perspective. Messier has been involved in research on understanding and treating OA for more than 25 years. His current work looks at the biomechanics of obesity among adults aged 55 and older.
He says extra weight also puts added stress on joints, impacts movement, affects gait (how a person walks), increases foot pressure, and decreases strength.
Messier notes that people who are overweight or obese have a higher risk of OA and the progression of the disease is greater. Every excess pound of body weight puts an additional four-pound stress on the knee, he explains, adding, "A weight gain of about 11 pounds over a 10-year period causes a 50 percent increase in the likelihood of developing OA."
Messier points out that OA is the leading cause of disability among older adults. It affects about 27 million older adults in the United States.
In looking at the biomechanics of walking, Messier comments that being overweight can change an individual's gait, thus causing or exacerbating joint pain. In addition, obesity creates more pressure on the feet. This pressure can contribute to plantar fasciitis, a painful inflammatory condition caused by excessive wear to the connective tissue that supports the arch of the foot. Obese individuals - those with a body mass index (BMI) greater than 30 - are five to six times more likely to have plantar fasciitis than individuals with a normal BMI (18.5 to 25).
In addition to joint and foot pain, obesity lessens a person's physical strength, which can impact activities of daily living.
"At first consideration, one might think obese individuals are stronger than normal-weight individuals," said Messier. "However, when you consider strength relative to body weight, obese people tend to be much weaker." He says this is because excessive fat in obese individuals infiltrates and weakens muscle tissue. Fat cells also release cytokines, chemicals that increase inflammation. Cytokines can also get into the joints and degrade cartilage.
The pain and disability suffered due to OA, plantar fasciitis, and loss of strength can cause a vicious cycle. When physical activity is painful, people tend to become more sedentary, and that inactive behavior can result in even more weight gain.
But there is good news. In his work, Messier found that weight loss and exercise can improve function and reduce the pain from OA. His research shows that a five percent drop in body weight, combined with a moderate exercise program, results in a 24-percent increase in function, and a 30-percent decrease in pain over an 18-month period. For a 250-pound individual, this translates to a weight loss of 12.5 pounds with moderate physical activity, such as walking 30 minutes a day, five days a week.
The American College of Sports Medicine is the largest sports medicine and exercise science organization in the world. More than 20,000 international, national, and regional members are dedicated to advancing and integrating scientific research to provide educational and practical applications of exercise science and sports medicine.
American College of Sports Medicine
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