Minni - muscle recruitment? I'll try.....!
Put a Ferrari alongside an Astra. Empty fuel tanks and put back a gallon in each - now tell the drivers to go as far as they can. Which one will go the furthest?
Which one are you?
What the article is getting at is how we can train each type of muscle fibre to act economically (Astra) even if they start out fast (Ferrari). So on long slow runs when layer 1-5 (in the example), conk out we can call on 6, 7 and so on.
Now here's the trick - if we push too hard then 6, 7 etc never develop the Astra charactersitics but stay as a Ferrari (by robbing fuel - glycogen). We don't notice,
We arrive at mile 18 feeling brilliant, but in fact by mile 21 we're dead because fibres 6 etc were never properly converted....and by then it is too late of course. Gobble all the gels you like at that stage and the Ferrari muscles will just suck it up.
Solution: long slow miles early in training to wean the Ferrari fibres off glycogen and adapted to economic, fat burning for as long as possible.
Now read the article again please, to make sure I'm not barking up the wrong tree!