Can someone please explain the different adaptations we get from work “over” FTP vs the work “under” or just below?
The consensus is that both are required to get faster but I still don’t really understand why.
Can we use this example? An athlete has a budget of 400 TSS per week and spends 80 of it on intervals and the rest on endurance. Obviously 80 TSS spent at 105% of FTP will give them less net time “in zone” than if it was spent at 95% of FTP.
What would the two outcomes look like for athlete A that spends all of his or her 80 TSS “over” vs athlete B that spends all of theirs “under?”
I am certainly no expert, but I think a reasonable parallel is this (and someone please call me out if this isn’t correct):
Imagine that you can squat 300 lbs for 10 reps, and equate this to your FTP. Now, imagine doing some of your workouts at, say, 310 lbs or 320 lbs for 3 or 4 reps, vs. doing 290 lbs or 280 lbs for 12 or 13 reps.
My understanding is that more weight for fewer reps generates a different muscular adaptation than less weight for more reps. And I believe something similar holds true for training over and under FTP, including improving your body’s ability to clear lactate at efforts above your current FTP.
Threshold work allows you to sustain high aerobic output longer (i.e. increased lactate threshold), whereas vo2 max work allows you to increase oxygen uptake and delivery capacity (stroke volume improvement = a stronger heart pumps more blood per beat).
To your TSS question, TSS is not created equal, and given the high fatigue cost of vo2 max training, you simply can’t fill your boots with it all year, and why you’ll find most cycling plans periodise vo2 closer to your goal events.
Over FTP you are using some different pathways. Your are burning more glycogen and creating lactate and hydrogen ions. Above FTP you are also using larger motor units (faster twitch muscles).
There isn’t really a difference between just over or just under, because the adaptations occur within a broad range and the specific FTP number has a wide margin of error. It’s easier to train below, and you still get mostly all the benefits, so that’s why people suggest to train there (aka sweet spot) or do intervals where you vary going above or below.
I like doing over under workouts because they’re fun and not that hard compared to sitting right on your threshold number for however long.
TLDR: don’t read into it too much, one or the other won’t be the difference between you being as fit as possible.
Don’t know enough physiology to answer your question in details but there is certainly mental side to it: as @AJS914 described, over FTP you are producing unsustainable amount of lactate and feeling more discomfort. When you go below FTP your body produces less of it and you have chance to consume already existing lactate i.e. going through producing/clearance loop. Basically, you should be physically able to continue but your legs have still burning feeling and you have to push through it.
Whether you need this resilience, is separate question. It is definitely useful when participating in spirited group rides. I am riding mostly solo, so I don’t need it and always substitute them with sustained efforts (either below or above FTP, depending on mood)
I’m really trying to understand the physiological consequences of one vs the other. Take two identical athletes and train them as described; how would their outcomes differ?
I believe that he is talking about the 1977 Hickson study. He doesn’t have the details quite right. It was 3 days per week of 6x5min @ vo2max and 3 days of running starting at 30 minutes as hard as they could.
The author is Hickson (1977)
Linear increase in aerobic power induced by a strenuous program of endurance exercise