What it feels like: Your knee aches and may throb or swell.
Is it serious? It's usually not, but talk to your doctor, especially if you have trouble walking or bearing weight.
What causes it: There are many reasons for knee pain, but walkers can usually blame it on inflammation from overuse, says Dr. Flynn. Common underlying problems include tendinitis, osteoarthritis, and Runner's Knee, a term referring to misalignment of the kneecap. Overpronation, when your feet roll inward when you walk, can also strain your knee.
How to prevent it: Your quads control kneecap movement, so strengthen those muscles. Try lying flat on your back, lifting one leg 45 degrees off the floor quickly, then slowly letting it down until your heel is one inch from the floor. Repeat 10 times for three sets. If you overpronate when you walk, an orthotic inserted into your shoe may correct your form and keep your kneecap in line, according to Dr. Donley.
How to treat it: "Back down on exercise until your pain gets better," says Dr. Donley. An over-the-counter anti-inflammatory medication, such as Motrin, can bring relief and reduce swelling. Chronic knee pain sufferers may sometimes require steroid injections.