Focusing on either aerobic conditioning or resistance training – especially moves that target the quadriceps muscles, which help support the knee – is the most effective exercise approach for reducing pain from knee osteoarthritis (OA), according to a study recently published online in Arthritis & Rheumatism.

Experts have long known that exercise can help reduce pain and improve function for people with knee OA. But what type of exercise is best, and how much, are subject to debate. The new study, an analysis of 48 previously published trials, aimed to provide answers.

The researchers looked at randomized controlled trials (the highest-quality type of study) designed to evaluate exercise in people with knee OA. Some of the trials involved aerobic exercise (such as walking, cycling or swimming), some involved strength training, and some involved both types of exercise performed during the same session.

Most trials showed a positive effect on pain and disability, reducing pain by almost 20 percent on average, a “small but important” effect, says study co-author Carsten Juhl, PhD, of the Department of Sports Science and Clinical Biomechanics at the University of Southern Denmark. But exercise programs that focused on either aerobic exercise or strength training worked best; those that combined both approaches were less effective.

The researchers aren’t sure why. They theorize that people who follow mixed programs might not get enough of either type of exercise to achieve the maximum benefit. Something may also be happening at the molecular level to decrease the body’s response to both types of exercise, they say.    

“I was surprised that we found that interventions with different types of exercise within the same exercise session were less effective than sessions with only a single exercise type, and I think that this should be investigated in direct comparisons,” says Juhl.

None of the trials examined in the current study looked at performing aerobic exercise on some days and strength training on others, says Juhl. Yet that is what public health experts recommend for people with OA, both for their joints and their overall health, says Leigh F. Callahan, PhD, professor of medicine at the Thurston Arthritis Research Center at the University of North Carolina at Chapel Hill. The general guidelines recommended by the Centers for Disease Control and Prevention (CDC) call for 150 minutes per week of accumulated moderate aerobic activity and strength training two or three times a week.