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People who engaged in weight lifting and other forms of strength training were less likely to develop knee pain and be diagnosed with osteoarthritis (OA) as they approached their senior years, a new analysis of Osteoarthritis Initiative data found.

Rates of knee pain and symptomatic and radiographic knee OA were all lower by about 20% among those reporting a history of strength training at some point, versus those who never tried it, according to Grace Lo, MD, MSc, of Baylor College of Medicine in Houston, and colleagues writing in .

Specific, fully adjusted odds ratios were as follows:

• Frequent knee pain: OR 0.82 (95% CI 0.68-0.97)
• Symptomatic knee OA: OR 0.77 (95% CI 0.63-0.94)
• Radiographic knee OA: OR 0.83 (95% CI 0.70-0.99)

Some may find the results surprising. Past studies focusing on Olympic-class male weightlifters had found , leading to concerns that any form of strength training was risky, Lo and colleagues wrote. That was a mistake, they argued: findings from elite athletes "should not be generalized to the general population because their exposure (load per repetition, number of repetitions, and type of loading) differs from strength training activities in the general population," where the weights don't approach those typically used in competition. Indeed, the researchers noted, there are many reasons to believe training with moderate weights would help prevent OA.

To test that hypothesis, Lo's group drew on data from the , a joint program sponsored by the National Institutes of Health and co-funded by major drug companies, and intended to represent the general population. It began enrolling community members at four sites in the northeastern U.S. in 2004-2006 who were then followed until they died or were lost to follow-up. Participants reported various aspects of their previous histories and submitted to periodic questionnaires and exams (including x-ray imaging), most notably at the 8-year mark after enrolling, i.e., during 2012-2014.

The questionnaires included items about leisure activities, including strength training. Specifically, participants were asked which they had engaged in for at least 20 minutes on a given day (not necessarily in one continuous block) at least 10 times during four periods in their lives: ages 12-18, 19-34, 35-49, and 50 and up. Respondents were also asked to list the three activities they engaged in most frequently. Those who included strength training were then considered to have a history of strength training for purposes of the current study.

Also, for each life period, participants were queried as to the frequency with which they engaged in strength training. These responses formed the basis for categorizing participants as having had "low," "middle," or "high" exposure to such training.

X-rays were taken at site visits scheduled every 4 years, at which point knee pain was also assessed. The key question was whether participants "had pain, aching, or stiffness in or around your right/left knee on most days for at least one month," with "most days" specified as at least half the month.

Out of the original 4,796 enrollees in the program, 2,607 were included in the study. Most of those left out had missed the 8-year return visit or didn't complete the activity questionnaire; a few lacked x-rays or sufficient data on knee pain.

Mean participant age at the most recent evaluation was about 64; men accounted for 44%. Body mass index values averaged 28.5.

Just over two-thirds of included participants reported no history of strength training. Some 13% said they had done some only at age 50 or later, and another 6% said they had engaged in it only after turning 35. Just 0.9% indicated that they had done strength training throughout their lives.

Frequent knee pain was reported by 40.5% of those with no strength training history, versus 36.9% of those having at least some. There appeared to be a modest dose-response relationship, as 39.8% of participants in the "low" exposure group had knee pain, compared with 35.9% of the "middle" group and 35.3% of those classified as "high." Adjusted odds for having frequent knee pain were lower by 26% in the "high" group versus participants with zero past strength training (P=0.008).

Results were similar for radiographic and symptomatic knee OA. Radiographic OA was seen in 60% of those with no strength training experience versus 53% of participants with some, and "high" exposure was even more protective. For symptomatic OA, the corresponding crude rates were 29% and 24%, respectively. A history of knee injury, a strong risk factor for subsequent OA, was actually more common in those who had performed strength training (53% vs. 47%).

Lo and colleagues were intrigued to find that participants who had only started strength training after age 50 enjoyed the same and perhaps even stronger protective benefit compared with those whose experience was at younger ages.

"Exercise trends over the past few decades may have influenced results. Strength training has become increasingly popular over the past few decades," the group noted. "Exposure to strength training at younger ages was less common and may predate the widespread adoption of strength training machines in local fitness centers. Participants in this study would have been around ages 12-18 in the 1950s when fitness gyms with a focus on strength training were not ubiquitous."

Other cautions about the study included the possibility of unmeasured factors that may correlate with a person's pursuit of strength training and that also modify risk for OA. As well, the study relied on participants' potentially faulty recall of past behaviors.

Overall, wrote Lo and colleagues, the findings "support the idea that the medical community should proactively encourage more people to participate in strength training to help reduce their risk of osteoarthritis and other chronic conditions."

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