I cant seem to run very far for very long, when I do I cramp up bad in my sides and my shins. today I jogged a half mile and had to drag myself home the because both my shin mucles locked up so tight I couldnt bend my ankles. I've been trying to work on my cardio capacity, I wanted to run a marathon next fall with some friends, but I cant seem to stop my mucles from cramping up really bad. Any advice? maybe it's my diet, I dont take in much carbs anymore.