This is not really a proper training session.
Go 40 mins aerobic pace so you can still talk. An ideal one for a young kid to cycle around with you.
Then for your last 1k go flat out at faster than race pace for a 5k. (Make sure aforesaid young kid knows where you will be in a few mins time and ideally has no big roads to cross!)
I think the idea is to trick your body into thinking it has run really fast for longer than it really did and to extend your lactate threshold (ie the point where your body aerobically conks out!)
I tried it, easier than an interval session i must say…so therefore probably not as good. But it is always good to mix things up