Depending on your age, lifestyle, and a host of other things, it could also be a sign of peripheral artery disease. This is where the arteries begin to plug up - very slowly, and the extremities are the first to be noticeable. If this happens mostly in your legs and feet it is called claudication, a subset of PAD. If your legs cramp or get very sore while walking any distance (generally, but not limited to, the calves), it could easily be claudication. Diabetes is a heavy contributor to this condition and half of the Americans who have diabetes, don't know it.
There are some very modern techniques for dealing with these conditions.