I can trust the input. So, if I approach an interval training, I’d look up what I am supposed to do based on the stimulus. For example, I could ride 6x3min @90% max HR, 2 min rest. I’d then trust this input to be a stimulus and basically lay back and let my body figure out the adaptation and come back faster the next time (if equally well rested).
Or, I could force the progression. Then I’d, for example, look at the total work that I performed the previous session and increase it by 1-2% even if it means that I have to push some intervals above 90%.
I try to figure out how to balance both approaches, since I think both are important aspects of training:
You should aim for the specific stimulus you are after.
You should progressively overload.
I try the following:
I start with (1). I figure out what I am after and then adhere to the lower end to the prescribed stimulus that should be enough to elicit adaptations.
Then, for a while, I increase my output in small increments.
When I feel that I am leaving the stimulus, meaning that I start to overshoot (better would be to assess before that point…), I re-assess by performance reverting back to the starting point. If my training worked, I’d be able to increase my performance with the same input.
You always try to improve. Whatever HR or Power target or target % you are using, at the end of the day it’s just a guide. If you can do more (either harder or longer), you do more as long as it feels manageable from a recovery perspective.
Putting existential decisions to one side, I offer up this
Some might think it was on a little bit of paper I found in an xmas cracker, but no, it is from the historic contributor to this board known as the_cog in his K.I.S.S. training thread.
A take on the more widely used “don’t let perfect be the enemy of good”
Minimum Effective Dose (MED) – do least possible effort that still triggers adaptations. This is safe bet that facilitates long term consistency and leaves room for longer progression before hitting plateau.
Maximum Recoverable Volume (MRV) – do as much as possible that you still can recover for next hard session. This is very personal, and you can burn out multiple times before discovering your limits. You may think that by approaching cautiously you can find your limits safely. Not really, it may take couple months and once you are so deep in hole, it can take very long time to get back.
TR AT + RL/GL can help you with both approaches by tuning AT balance between conservative ↔ aggressive.
But as @AJS914 says, 1% is nothing. You are very likely in better place by keeping interval as prescribed and consuming more calories and/or sleeping 30min more