"After years of war, my ancestors gave up their barbaric practices and bent the knee to their new kings," says Roose Bolton at one point in the saga, "Game of Thrones."

In that tale, defeated factions repeatedly bend their knee as an act of submission to a victor.

But all that up-and-downing doesn't seem to cause the characters any joint trouble. The same can't be said for binge-watching fans of the series.

The incidence of knee osteoarthritis has doubled in the past seven decades, according to a study in the Proceedings of the National Academy of Sciences.

Knee osteoarthritis now affects a third of Americans over age 60 and is responsible for more disability than almost any other musculoskeletal disorder. It's why 3 million women and 1.7 million men are living with a total knee replacement.

What accounts for this?

It's not just being overweight or living longer. The researchers say it is from specific factors you can control, meaning knee osteoarthritis might be more avoidable than previously thought.

Inactivity — not exercise — leads to thinner knee cartilage and weaker muscles responsible for protecting joints.

And the epidemic of chronic low-grade inflammation that affects so many Americans because of diets high in refined foods, processed carbs and excess bad fat further erodes cartilage-building, even if you are not overweight.

Your risk of knee osteoarthritis can be slashed if you walk 10,000 steps a day and avoid the inflammation foods like added sugar and syrup, processed grains, and saturated and trans fats.