Aerobic efficiency is measured by the maximum output sustainable without accumulating lactate, while peak aerobic output is measured by VO2 Max.

“W which is what is the maximum output you can sustain while still exclusively utilizing uh your Aerobic System so therefore you're not at all accumulating lactate um and again I'm being a little a little bit um um uh sloppy in my terminology there and we can maybe clear that up a bit a bit later but but basically you know what's the maximum output you can sustain without accumulating net lactate um and at the other end of that Spectrum what is the maximum utilization you have of oxygen which corresponds of course not to your maximum output but more importantly your maximum aerobic output”