I'm an enthusiastic but technically probably very poor runner. Every time I start upping the mileage, I get pain in my left calf that feels a bit like a cramp. It can last for up to three days after a run, so it's not a cramp. It's always in my left calf, so I think it may be something to do with my running style. Can anyone point me to any good articles on running style, and what over and under pronation is, and whether you can correct this. Also, where I should be landing on my feet, I've heard conflicting stories about whether to land on you heel, or on flatter foot. I'm doing the London marathon in April, so any advice that might help would be greatly appreciated.