"Are you still pounding the streets in your favourite Dunlop Green Flash?" Kerry asks. "No wonder you've got dodgy knees. Everybody's running style is different and requires different shoes depending on whether you're, say a neutral (efficient) an overpronator (feet roll inwards) or a supinator (feet roll outwards). Most specialist shops including Sweatshop and Runners Need offer a free gait analysis service to help you chose shoes that improve comfort and cut the risk of injury."
How much varies