After about four minutes of sustained, rhythmic activity oxygen consumption plateaus.

For the duration of the exercise session, blood pressure stabilizes, an equilibrium is maintained between energy required to sustain activity and energy produced by aerobic metabolism--thus lactic acid does not accumulate faster than it can be flushed away--and activity can continue (seemingly) indefinitely." We have numerous steady rate levels: sitting, watching television; dancing vigorously to a DJ's extended mix; running a marathon, and so on. The more active steady rates represent a measureable percentage of our maximum heart rate, and are helpful in prescribing our aerobic training intensities.