This might the single most sensible document I have ever seen about steady state. The issue that you deal with when you are talking about exercise physiology is that not all human's react the same way to the same training stimulus. We are not machines, so different outcomes are certainly possible and the "perfect" definition of steady state is elusive.
It helps me to remember the basic objective and go from there.
Objective: Row 2000m faster
Rowing 2000m involves using multiple different energy systems in the body. There is reasonably strong evidence that organizing training to focus sessions on each energy system yields superior results than just pushing every session as hard as you can. So, how do you do that?
By tailoring the intensity of each session to a specific purpose and arranging sessions so that there is adequate recovery time between sessions focused on the higher end of the scale.
Steady State training is the training that is focused on two energy systems. The first converts fat into energy for muscles. This process does not produce any lacate. The second converts carbohydrates (in the form of Glycogen) into energy for muscles. This process does produce lactate.
There is an additional wrinkle. Lactate is not just a waste product. It is also used by the second system to produce energy, up to a certain intensity. If you are below that intensity, then lactate levels will be steady. If you are above that level, lactate levels will rise. The speed at which they rise, depends on how far above the threshold you are.
Most folks achieve a "Steady State" lactate level somewhere in the range from 1.5mmol/l and 2.0mmol/l. Generally, the fitter the individual, the lower the steady state lactate level.
The reason that lactates are the preferred measurement for this is because it is a direct measurement of what you are trying to accomplish. You want to make sure that the training for these base energy systems is not too intense because of a nasty twist. Once you go beyond the steady state threshold, not only are you increasingly relying upon glycogen and accumulating lactate, you are also effectively shutting down the system that produces energy from fat. This concept is call "The Crossover" and was published a while ago.
This, in essence is why shorter harder sessions do not have the same effect and longer easier sessions.
The big problem is that lactate measurement in messy, error prone, painful, complicated, expensive and makes you look like a lunatic at the gym. So, what do you do? Well, if you are like me, you decide the live with the perforated fingers and weird looks and take the measurements anyway.
But if you aren't on the lunatic fringe, there are options. I think the best is using HR. It's not perfect, but if you train to a strict HR cap in your steady state sessions, you will probably be OK. The thing is that you should work to have your intensity dialed in so that you only get near your cap very close to the end of the session. The key is small adjustments.
If you aren't into HR based training, the next is to work off of 2K power. This is a fraction of the avg power of your last all out 2K test. In general, around 55% of 2K power. You train at that power until your next 2K test, and then adjust accordingly.
It's boring, but it works. One thing to consider is doing 2 45 minute sessions instead of 1 90 minute session. It's easier on the butt and back and provides just about the same benefit.
