@FRANK When doing long intervals like sweet spot or tempo and your HR drifts outside the zone in the latter end of the workout, what should one be doing, maintain the power zone or drop the power to maintain the zone with HR?
I think first @ryanolson you want to determine why you are getting heart rate drift and that will determine what if anything to do about it .
Would require us to go in a look at your data otherwise the answer is just a guess.
Let us know the ‘why’ first - let’s start there
That is tough to answer, maybe just accumulative fatigue over the workout or dehydration due to not drinking as much in the cold or just getting back into shape (yes the ftp was adjusted down). My HR zone for sweet spot is 162-170 bpm and in like a 4x15, I may start to see 172 on sets 3 or 4 with 5 mins to go so I back off a tad, and in sets 1 and 2 would be like 150-165.
As your aerobic engine improves you should see less drift and more consistent heart rate averages between the efforts. Fatigue is most likely cause but also dehydration and heat can be a factor. 4 x 15 minute is a pretty big workout! With a 4 x 15 minute workout from the first interval to the finish of the last one you are nearly 90 minutes of riding and 100 TSS. So that is a good size workload. If you have a really good size base yo would like to see your heart rate not go over sweet spot. 170 bpm being your high end and going up to 172 bpm too drastic.
With a workout like 4 x 15 minutes you don’t need to be at 97% of your FTP for the first intervals. Ride at 92%. If you do 97% for 4 x 15 minute that is approaching a 40km TT effort, of course with a bit of rest. But that is a big effort.
Again with sweet spot you are looking at getting advance aerobic training. The difference in workload from riding at 92% to 97% in this workout would be 10 TSS, same as 12 minutes of zone 2, so not all that much. The important thing is to do an aerobic workout and if your heart rate starts to drift up over threshold than you are taxing it too much and taking out one of the best benefits of sweet spot training, the ability to recover better since you are under threshold.
If I maintained the same output I probably would have gone higher than 172 so this basically tells me it was right to back off a little once I started to surpass 170. Yeah, I figured it was a getting back into shape thing too. Cool fact on 12 mins of z2 = 5% load increase!