Lets break the tweet down
Decoding the tweet:
It is impossible to teach an athlete to ‘run fast when tired.’
---A bit of a face palm here. This is the entire point of training. To run as fast as you can when you are tired. What he probably means is that you cannot develop your top end speed while tired, which is true. However for a guy always talking about how being precise matters, he is not very precise in this instance.
The very nature of being in a state of fatigue negates the ability to run fast — the skill of speed is only learned when fresh.
---He's not wrong
Therefore, doing a tempo run followed by ‘fast’ 200s is, in fact, a useless exercise.
---Yes, it's useless for developing your top end speed. It's not useless for honing one of the other hundreds of parameters that goes into running. This statement as written is stupid.
The more you dig into exercise science the more it should become clear that even the experts know absolutely nothing in terms of the entire system. Just take one look at this metabolic pathways map. We focus on VO2 and Lactate threshold because those are parameters we can measure in the lab. But if you study the map you can see just how many processes and feedback loops go on in the entire biochemical process. Saying running 200s after a tempo does or doesn't do something just proves you only think you know what you are talking about. The true answer is we don't know what they do, but if people seem to be having success or failure with them, that should sway our opinion when we consider the art of training.
http://www.metabolic-pathway.com/fullMap.html