The Ingebrigtsens are ALL 1500m specialists FIRST for the most part - this thread and the Strava group are filled with NON-1500m runners - and I think they have mostly adjusted the training to fit the longer races - for example - KI and Sirpoc do 3x3200m reps and rarely or never do the 400m reps. For them I think this is a reasonable alteration - but for 1500m type runners I think it might be unnecessary. The original Ingebrigtsen training seems to concentrate on 400m 1k and 2k reps and nothing longer. That's what 1500m specialists should do IMO.
I also don't see a huge utility in long runs for 1500m runners. There was someone on the strava thread who said he never did ANY runs longer than 1600m and PR'd his HM time.
I also question the emphasis on so much Easy mileage - if the entire point of easy days is to recover - it matters not how many of those miles you do - perhaps it is only necessary to do some minimum mileage as just a way to make sure your body MOVES on those days and flushes all the waste products from your system.
I don't know. But it seems to me the THRESHOLD runs are the 95% training and all the other stuff - long runs, easy days, hills etc - those are last 5% training.
One last thing - using distance for the threshold reps I think is a mistake - CTL and other type measurements are a version of something weight lifters have known and used for decades - you improve your hypertrophy and strength based on Time Under Tension. 5 slow reps can beat 10 fast ones because the TIME the muscle is being subjected to stress is greater.
I think thresholds are the same - you don't target 10x1k or 25x400m - instead you target the hours per week. Look at 10x1k for Jakob versus 10x1k for a hobby jogger like me - a session like that is 50+ minutes for me - it might be HALF that time for Jakob.
It cannot possibly make sense for hobby joggers to be spending twice as much time doing threshold training as Jakob.
And since all these reps vary little in pace ( a few seconds per k faster or slower depending on the distance of the rep) - in the end all that matters is the TIME you spend doing threshold reps during any given week. And the distance of any specific rep might be mostly irrelevant.
As u get faster u naturally end up doing more threshold mileage even while keeping the total time the same.
Lots of slightly different ways to skin this cat.