A certified physical therapist says you should do these five things to protect your knees if you're a keen walker, hiker or runner

A man in running clothes kneels on a sports ground and looks closely at his knee, cupping it with two hands.

Lately my knees have been playing up when I run or walk too vigorously.

I assumed that was because of general wear and tear in the joint—then I consulted a physical therapist who specializes in treating patients experiencing chronic pain.