Maximal Lactate Steady State is an effort level that an athlete can continue at for an extended period of time without having to slow down, MLSS can be as much as an hour or possibly longer.
As long as the athlete maintains this effort level, their lactate level will remain constant. At any effort levels above this point the athlete’s lactate level will rise, and they will be forced to stop.
Also known as Lactate Threshold, or the Anaerobic Threshold.