I'm just getting into distance riding (60-100 mile rides). I find that often when I ride, I go fairly fast and comfortably for a bit, then all of a sudden it is like I hit a wall. My legs are cramping, and I just feel exhausted and uncomfortable, and for the remainder of the ride I am pretty much shot.
Any idea why this happens? Maybe I am just not in good enough shape, but I'm wondering if it has something to do with my blood sugar or something? How much should I be eating during a ride? And what is the deal with lactic acid building up in muscles? Is that actually something that is common? I've read about it but it is hard to say if that is what is going on with my legs.
I bet I sound like a total noob, but aside from biking recently, I have never done any sports or anything.
I've done some google searches for my questions, and I have gotten some good information but I was hoping some folks here could give their thoughts too.