Run Smart, Stay Strong

Experts detail how the high-impact activity of running strengthens bones instead of damaging them and 'how old is too old' to get into the exercise

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You've probably heard that running is tough on your knees—and even that it can cause long-term damage. But is this true?

Running is a relatively high-impact activity. Every time your foot contacts the ground while running, your body absorbs a force that equates to about two to three times your body weight.

It's easy to imagine this load going straight into your knees, and it sort of does. Your knees absorb three times more load during running than walking.

But this isn't a bad thing. In fact, running may help keep your knees strong and healthy—here's what the evidence says.

Designed to keep moving

Your body isn't simply a pile of bones and cartilage that gets worn down with every step. It is a living, dynamic system that grows and adapts in response to the loads that are placed upon it. And it needs a load to keep functioning.

Your knee joint is incredibly strong and designed to move. The cartilage inside your knee is a strong, flexible, connective tissue that cushions and protects the bones of your knee joint.

There is good evidence to show when someone's load is removed—for example, during prolonged bed rest or immobilization—their bone and cartilage begin to deteriorate.

What running does to bones & cartilage

We know running temporarily reduces the thickness of knee cartilage. This returns to normal a couple of hours after the run is finished.