The lactate threshold is the exercise intensity at which the blood concentration of lactate and/or lactic acid begins to exponentially increase. The reason for the increased lactate concentration in the blood at high exercise intensities muscle cells release lactate into the blood to be converted back into glucose by the liver (see the Cori Cycle): the high rates of ATP hydrolysis in the muscle release hydrogen ions, as they are co-transported out of the muscle into the blood via the MCT— monocarboxylate transporter, and also bicarbonate stores in the blood begin to be used up. This happens when lactate is produced faster than it can be removed (metabolized) in the muscle. When exercising at or below the LT, any lactate produced by the muscles
