What’s the difference in stimulus between continuous threshold and intervalled threshold session

When you take short rests, your HR comes down a bit. This means you can have a higher average speed (minus the rests) for your session while staying in the proper "zone." If I do a 30 minute tempo run, I'm gasses and I probably ran too hard. If I do something like 5x6 min, I finish feeling good, I averaged a faster pace than I would have continuously, and I recover faster.

Okay yeah this makes sense. That has my wondering then why change session length at all if you Jakob and you wanna maximise speed at threshold why wouldn’t you just do 20x400 everytime instead of doing his 10x1k and ect

Check out "modifying Norwegian approach to lower mileage thread". This is discussed quite a bit in there by sirpoc and others in the epic, almost 100 pages. He started off doing 400s, at around 10k (ish pace). This would generate the same amount of lactate roughly as say 10*1k at 15k pace or 3*3k at around 25-30k pace, with the huge caveat that after the 400s the next day, he would feel a bit more beat up. So , for a non pro who probably doesn't need that extra 1% or the icing on the cake, it's safer to stay at moderate but still faster paces, then go again 48 hours later. I think what a lot of answers you are looking for is in that epic thread.

Ima guess that Bakken chose this workout format so that he had time to test. Ingebrigtsens copied Bakken. It seems to work so they stuck with it. But anyone going by feel can change it up however they like.

Thanks for the response, I read like 8 pages of that thread but I seemed have to missed that. Do u know where they specify why I then if the 400s cause too much recovery for my use would I then just choose one session that suits me best like 10x1k without varying the session at all week to week as perhaps that session for me has the best threshold stimulus to recovery. Or is there benefits in variation.

At a certain point, you're going fast enough that it becomes stressful. The idea is there's kind of a band of paces and efforts that offer the most aerobic benefit with the least recovery time. Why not do 160x50? Because those 50m would be pretty fast and put a lot of stress on the muscles.

I agree but why not choose one pace like the 1x10k instead of varying. What is the benefits to variation. Different uses musclses slightly differently so can fit more in?

That thread is long, but well worth it. It's quite linear in time, it's nearer the middle to current point I think this is discussed. I think sirpoc and KI both dropped the 400s. sirpoc being quite communicative especially if you pm him on Strava or on the group some guy set up dedicated to the thread has said (I believe) that there is no reason to do "other" distances if you don't want to, but he does simply to stop himself getting bored and to have some faster stuff in there and also slower but longer just to get used to longer efforts but that current reps which are 10*1, 3*3200 and 6*1600 despite the different speeds, do in fact average out to generating the same lactate. It's only the 400s I can also remember him specifically mentioning that made him feel beat up more than the rest. It seems to be massively working for both sirpoc and Jakobs hobby jogger brother. Ultimately, that's who we should be following and caring what they do, not Jakob. It has no relevance to 99.9% of letsrun readers.

Yes, your mechanics and muscles are all working a bit different at different speeds. Go look at old Igloi training, kind of the same idea. You might see things like 30x100m for an 800m runner. Maybe they run these at, idk, 17 seconds. That's 3000m of work at 4:32 pace. Compare that to 10x1k at 5:32 pace for the same 800m runner. The HR might be in the same zone during both of these workouts, but they muscular stimulus is very different. 4:32 is much closer to the race pace of an 800m runner than 5:32 pace is.