Many people worry that running ruins knees. But a new study finds that the activity may in fact benefit the joint, changing the biochemical environment inside the knee in ways that could help keep it working smoothly.

In my many decades as a runner, fellow runners and nonrunners alike have frequently told me that I am putting my knees at risk. The widespread argument generally follows the lines that running will slowly wear away the cartilage that cushions the bones in the joint and cause arthritis.

But there is little evidence to support the idea, and a growing body of research that suggests the reverse. Epidemiological studies of long-term runners show that they generally are less likely to develop osteoarthritis in the knees than people of the same age who do not run.

Some scientists have speculated that running may protect knees because it also often is associated with relatively low body mass. Carrying less weight is known to reduce the risk for knee arthritis.