Arthritis is a growing problem, rising along with the rates of aging Americans. Fifty million Americans have been diagnosed with arthritis, and that number is expected to rise to 67 million by 2030, according to the U.S. Centers for Disease Control and Prevention. The good news is massage therapy is an effective way to address arthritis pain and stiffness. New research indicates that although exercise also benefits arthritis sufferers, not enough people with arthritis are engaging in the recommended amount of exercise.

Physical activity can help people with arthritis better control and lower pain, and improve general function. Some studies indicate exercise may delay or even prevent disability in people with arthritis, said Dorothy Dunlop, associate professor of medicine at Northwestern University Feinberg School of Medicine and lead author of the study.

Despite exercise’s positive effects, the new study shows more than 50 percent of women and 40 percent of men with arthritis are “virtually couch potatoes.”

This is the first study to use a device to objectively measure the physical activity of people with arthritis and determine if they meet federal guidelines, according to a

university press release. Past research relied on self-reported accounts of exercise and activity.

Researchers asked more than 1,000 people with radiographic knee osteoarthritis to wear an accelerometer—a small, sophisticated device that looks like a pedometer—to measure their physical activity for one week during waking hours. The participants are part of a larger national study called the Osteoarthritis Initiative and are 49 to 84 years old.

“We had assumed that people might be overstating physical activity in past self-reported data, but were surprised to find that the physical activity rates were much, much lower than what was previously reported,” said Dunlop.

The federal guidelines recommend that adults with arthritis participate in 150 minutes per week of moderate-intensity, low-impact activity. That amounts to an average of slightly more than 20 minutes per day. Previous studies estimated that a quarter of people with arthritis met those guidelines.

The study was published in Arthritis & Rheumatism‘s August 2011 issue.