Anaerobic threshold (AT) has long been known as one of the most important benchmarks in endurance sports. AT marks the intensity (speed or power) at which the production rate of lactate in the muscle equals the clearance rate of lactate. AT marks the highest possible intensity, which can be sustained without accumulating lactate. The exercise duration in this case is mostly limited by the availability of carbohydrates, which drain quickly at the intensity of AT
The top right graph shows the lack of pyruvate (or lactate, grey line) and the actual lactate accumulation (purple). If you look back to the lactate production and lactate combustion, you can identify the gap between both at intensities below anaerobic threshold (below the crossing point of both). The gap between gross production and gross clearance is the lack of pyruvate. Or in other words: the amount of lactate that could be cleared additionally to the gross production. Lack of pyruvate curve is shown in mmol/l/min of lactate clearance. It shows the ability to recover from lactate accumulation in relation to the intensity (speed or power). At anaerobic threshold it runs to zero – the aerobic metabolism is saturated with lactate and no additional lactate can be combusted.
The purple curve shows the rate of lactate accumulation. This occurs at intensities higher than anaerobic threshold. The steeper the curve, faster lactate accumulation at any given intensity.