Thats the theory Mac but its never rung true to me (not that I have any firm evidence to the contrary, just a gut feeling). I accept its too low for lactate runs but not so sure about the aerobic side of things. The Hadd document has "Joe" running in this range when he's relatively new to the schedule.
I think its more likely, rather than it being some sort of "dead zone" where its not helping anthing inprove, the disadvatage of 75-80 running lies in that you can get similar results aerobically running at 70-75% while also managing more miles, more time on feet and with less chance of injury.
Like I say, just a gut feeling though.
Edited: 22/11/2012 at 19:33