[andor]

lactate production rate (indicator for fat burning

The body's VO2max potential can be used by solely burning carbs

Actually you mixed them both up. In aerobic (with oxygen) exercise, you mostly burn fat. In anaerobic exercise, you burn glucose and glycogen and produce lactic acid through lactic acid fermentation. The important metric for anaerobic performance is not acid production rate, but acid tolerance of the muscles, because high acid levels lead to fatigue.

http://en.wikipedia.org/wiki/Anaerobic_exercise

[KobaQ]

To clarify my context: For a given effort, the body always uses anaerobic and aerobic systems. The higher the fraction of the energy from the anaerobic system, the higher the lactate production rate. The lower the lactate production rate, the more energy comes from burning fat.

Lactate can be further used to create ATP, but this process needs oxygen as well. Hence, a good VO2max helps to get rid of lactate, which was created in the anaerobic process. When measuring the lactate threshold by solely the lactate concentration, it's difficult to distinct between high production / high reduction and low production rates. Good VO2max can conceal weak fat burning abilities. Therefore often the lactate production rate by a given effort (typically maximum effort) is used as indicator for the fat burning capability.

(Hope that makes sense, English is not my native language :-) ...)