Many people think running causes knee arthritis, but that's a big fat myth. Given the insane amount of force that bears down on a knee with each running step – about three times as much as a walking step – it would make sense that pounding the pavement at full speed would wear away cartilage around the joint more quickly than leisurely walking, putting runners on a faster track to knee arthritis.

However, for years, studies have shown that running does not, in fact, increase arthritis risk any more than walking, which has left experts scratching their heads trying to figure out why. For runners to have no greater arthritis risk than non-runners, there must be another knee-protecting factor at play. Finally, a new study published in Medicine & Science in Sports & Exercise in September has found it.

Researchers from Queen's University in Canada gathered a small group of avid recreational runners with no history of knee problems to see what really goes on biomechanically with each running step versus walking step. Using floor sensors and motion-capture technology, they were able to gauge the force of the participants' steps when running versus walking, as well as how many steps each person took and how long their feet remained in contact with the ground.

As expected, the participants' peak knee loads – the amount of force bearing down on the joint with each step – were much higher during running than walking. But when measured over the same distance, walkers took many more steps than runners and their feet remained on the ground for much longer during each step. This was an 'aha' moment for the researchers. They realized that, whether you run or walk, the cumulative peak force on your knee over a given distance will be the same. Therefore, running wouldn't necessarily cause any more cartilage damage than walking – or increase your arthritis risk.

"Even though the peak force you experience with every step is much higher when running than walking, the average force over given distance is equal," says lead study author Ross Miller, now a kinesiology professor at the University of Maryland. "This gives us a biomechanical explanation for why running doesn't increase arthritis risk."

Miller points out that if you already have knee arthritis, running and walking may worsen the condition. But if you have relatively healthy knees, you now have one less excuse not to lace up the sneakers and hit the road.