You ever sit around and wonder why you're not 4 seconds faster than the fastest man to ever live? Curious why your very first try was merely on par with gold medal olympians? You're too scared of pushing it. That's what's holding you back. It's not a lack of a lifetime of training or freak genetics, you're just scared to give it your all. Running is a lot like the brain in the sense that we only use 10% of the muscles in our legs, once you get over that fear of taking those bad larrys out of the holster then you too can't run faster than ever imaginable. Listen to the 40 year old singer, she'll tell you.