NEW YORK (Reuters Health) - Certain activities may be more likely than others to increase older people's risk of developing osteoarthritis (OA) of the knee, Dutch researchers report.

People who engaged in more activities producing high mechanical strain, such as tennis and dancing, were at greater risk of knee OA, while "low muscle strength" activities such as fishing and light household work were also associated with arthritis, Dr. Lisanne M. Verweij and colleagues from VU University Amsterdam found.

"We emphasize that physical activity should be recommended for older adults as it has numerous benefits for health and functioning," they write. Nevertheless, the researchers add, their findings suggest it could be important to identify which sorts of activities should be avoided, and which types of exercise older people should be encouraged to do.

Evidence on the relationship between physical activity and knee OA in older people is mixed, with some studies showing exercise boosts risk, others showing a protective effect, and still others finding no relationship, Verweij and her team explain in their report.

They decided to investigate four different components of physical activity to better understand how exercise may relate to OA. The researchers surveyed 1,678 men and women on their habitual physical activities, and scored them for four components of those activities: muscle strength, intensity, mechanical strain, and turning actions.

During 12 years of follow-up, 28 percent of the study participants developed knee OA. While the intensity of physical activity and the amount of turning action involved didn't affect OA risk, the researchers did find that high mechanical strain activities -- for example, volleyball -- boosted risk, as did engaging in low muscle strength activities.

"Our results are in line with the results of studies using measured muscle weakness or functional limitations showing that reduced muscle strength might increase the risk of OA," the researchers write.

Because they also identified a trend toward greater OA risk with low-mechanical-strain activities, they add, "this finding implicates that some mechanical loading of the bone is necessary to maintain healthy bone and cartilage structures."

Future research should determine how much daily activity corresponding to each of the four activity components they measured would be "optimal" for healthy joints, the researchers conclude.

SOURCE: Arthritis & Rheumatism, February 2009.

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