I've tried understanding it by reading all kinds of articles/MMA Conditioning, but I'm kind of at a loss. So blood sugar gets converted to Pyruvate which is then converted to lactate (which can be converted back to Pyruvate). This system kickstarts when the energy production of the Aerobic system no longer provides enough energy for the given exercise. What I don't really understand, is it the lactate that gets used as energy as in lactate gets converted to ATP? So am I correct in understanding that we fatigue when lactate gets accumulated in the working muscle and it can no longer be transported away to be used by the Aerobic energy system? I know this question is kind of all over the place but I find it hard to describe something that I don't understand. I hope the terms give some kind of indication of what I know which could be helpful in answering the question. Thanks!