My dd has similar complaints, only it's often her knees, as well as her shins.
It always seems to happen after a day where she has exercised a lot.
We saw the ped to rule out joint problems or other issues that could be causing this, and I've tried to find out what I can about what this could be. Everything I've found points to "growing pains". I had them as a kid, too. They really hurt a lot.
kidshealth.org has a good article on it, as I recall. If there really is an underlying problem, the affected area will be red or warm and the pain will NOT go away. Growing pains tend to happen at night, be worse with activity, they are not present all the time, and there are no symptoms of joint strain or other problems.
My dd likes to *run* (seriously, she can run far!) and on the days where she does laps around the playground
it is very likely she will wake up that night with growing pains.