Can someone help me with this please?...I'm in advanced P.E. ok ...we run the half mile every day, and it's pretty hard for me. I don't smoke or anything, even the smokers get ahead of me. I'm not a fat guy or anything ...It just seems like I don't have enough lung capactiy. Does anyone know why? Kids tell me they run 13 laps easy in football training. I couldn't even imagine I could do that. My shins start to hurt very bad..my feet cramp up and my thighs kill me, most of all I could barely breath when I run for a lot of time. And No I dont have asthma. Help me if you can, thanks.