It describes the production of lactate by the anaerobic system, its subsequent use by the aerobic system, and physiological reasons that improvement in one system needs to be balanced by improvement in the other.
This was all new to me, because I've never thought of training for racing. But I am now, and the information seemed to mesh well with some of the discussions here concerning lsd vs. high intensity training. There's a link to an article on "Steering" training that goes into that.
All this info is in aid of selling their product, but it seemed accurate. Anyone have any thoughts on it?