Craig has this great question:
Is it fair to say that the Minimum Effective Dose is not necessarily that dose which produces the maximum possible result?
Correct. The minimum effective dose is not going to get you all the way to your “best” though the idea of a physical peak, by definition, means that it is unsustainable. You’ll always be getting to is before falling off of it.
However, take a look at the graph below (and excuse “HOL” as the graphic designer later fixed it):
This is adapted from Power & Howley “Exercise Physiology” 7th edition. Further the modality studied was cardiorespiratory & steady state. In spite of that, you can see a clear point of diminishing returns: the first hour gets ~67% of the potential improvement, while 90 minutes get your ~82% of the potential improvement. To get 95% of your potential, it’s at least 3.5 hours.
So getting 82% of your potential (or ~25% more than you’d get from your first hour of training) requires 50% more time invested. This is still quite efficient and not insignificant. In order to get an additional 15-ish% (doing math in my head here) improvement over the 90 minute investment requires 2 more hours of training. That’s not very efficient, but if you have a paycheck or a gold medal on the line, it’s worth it.
So I’m introducing a new phrase: “Maximum Efficient Dose”. That is where the time invested is falling off, but the relative improvement would still be quite high. That said, your first investment of time and energy returns the greatest reward. You’ll also find just how talented you are at a given event or task quite quickly. There is no “magic” program or time investment that will overcome a lack of task-specific talent. Them’s the breaks, kid.
Skyler Tanner 
Great answer!