After having my left foot rebuilt a year and a half ago (thanks to too many marathons and other 15-mile days) I'm getting severe muscle cramps in my left leg-inside and above the knee. I'm also getting them in the calf muscle. These things come on suddenly, are bad enough to send me into shock, and make me fearful of having one while zipped up in a sleeping bag and tent. When one hits, I'm up NOW, usually screaming! My doctor's clueless; any thoughts on prevention?