Lactic acid is also known as milk acid. Lactate threshold is the point in exercise just prior to when your muscles can no longer cleanse themselves of this stuff. If you go past threshold, you are toasted…in a hurry.
Lactate threshold and lactation are two very different topics. The latter of which I am unprepared to discuss. [something to do with the feeding habits of mamals]
Anyway, there’s a connection between aerobic fitness and the body’s ability to process lactic acid. Cross the line into anaerobic exercise [huffing and puffing] and the glycogen stores in your mustles burn up like hairspray near an open flame. It leaves the athlete spent and unable to perform with any intensity. If you stay under the line, it’s possible to sustain exercise for a long period of time [e.g. endurance sports].
Intentionally exceeding threshold is what we call intervals. String together several high intensity intervals and you can raise the “ceiling” of your lactate threshold. Since January, for example, my threshold increased from 148 to 154. Professional cyclists can maintain as high as 170…of course with under-35 year old bodies, world-class coaching and training 9 months out of the year.