From the conclusion of the article: "go 8 seconds on and 12 seconds off for 60 rounds", where "on" is max effort, what does "off" mean? Is it medium effort or zero effort or is it something that you modify as your endurance increases?
"Sprint -> Jog"
or
"Sprint -> Walk"
or
"Sprint -> Lie on the ground, motionless"
?
I've been doing that for a long time (though it isn't exactly fartlek if you do it by yourself) to train for soccer, because it mimics the process of repeatedly sprinting and recovering. It's also easier on my joints than sustained running at a steady speed.
"Sprint -> Jog" or "Sprint -> Walk" or "Sprint -> Lie on the ground, motionless" ?