From @Stevemagness
One of my favorite workouts:
The “you decide” threshold
Set a total time you want to run at threshold (i.e. 25min)
Start at that effort. When you feel like you’re going over the edge, stop for 60sec, then start again
Repeat until you get to the total time of hard running
(https://twitter.com/stevemagness/status/1643625013595996161?s=61&t=XXSpAmOaXN5Qu99iLgjh5w)
This kind of threshold work sounds like Trevor’s 5x5s at threshold with an HR limit. 
I listen to Magness’ podcast regularly and they have been talking a lot about flux traning, float training, Igloi intervals, Marius Bakken, ingebrigtsen training, etc.
All of those methods are broken interval training.
It’s left me wondering why these kinds of intervals aren’t seen in cycling. They aren’t like Billat intervals which are all out and then with an easy rest period. One idea I came across is that hard running is very hard on the body so breaking it up allows them to do a higher volume. Cycling isn’t very hard on the body so we can do longer, continuous intervals.
I like Steve’s method because doing so individualizes to the athlete’s ability. Compare this to a set prescription it might be too easy for some, and too hard for others. I believe this applies equally to optimal run AND bike training. The perceived harder aspect to doing threshold efforts running relate to its higher neuromuscular or musculoskeletal stress (eccentric bouncing contractions) relative to the concentric contractions of cycling, but equally it relates to the individual’s durability (training level) for either exercise mode. Again - its very good advice.