How should I use my threshold heart rate?
When I do my 2-3 min intervals at 120% FTP, is this the HR I want to see?
I just increased my THHR on an 18 min hill climb at FTP.
Clearly, I can’t hold 120% FTP for 18 min.
How fast does THHR decay?
We have three energy systems, namely the oxidative, glycolytic and PCr systems, so you’d want to test across the range of each energy system and then use an appropriate “anchor” point.
Use your threshold HR for longer duration efforts that require more steady state efforts. It’s meant to steady, not stochastic efforts.
Use the ramp test, that tests VO2max (without the actual metabolic cart) to determine your maxHR from that effort, and see how the maxHR varies when doing these efforts. It might not be your absolute max heart rate, which could come from an effort somewhere between 3-6 minutes.
Short efforts, 3-8 minutes are meant to be done at >90% of VO2. What does VO2 mean? It can be 90% of the power and HR from the ramp test.
Longer efforts, >10 minutes should be done close to 90%. Some coaches say 90% + 1bpm and nothing higher.
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Do you mean that longer efforts should be done at VO2 or at 90% of VO2 (IOW, 90% of 90% 
)
Some say below 90% of the max HR achieved during the ramp/VO2max test.
Others say 90% of maxHR (from the last year)
And some say LTHR
These values can differ, and the can be quite close.
I can be quite confusing.
How does your HR compare when looking at:
- LTHR?
- 90% of maxHR?
- 90% of the max obtained when doing a ramp/VO2max test?
In your short VO2 intervals, HR would usually get above threshold HR during each interval. Maybe even very close to your HRmax in the later intervals. Somewhere in the 90% - 95% of HR max range is very common.
Some describe it based on breathing “like a fish out of water”
Threshold HR is what you would expect to see during decent periods of work at around your FTP (as per your 18 minute climb).
I haven’t seen anything definitive about Threshold heart rate decay rates.
There is a trainingpeaks article that might be interesting to you
And remember that HR is a response to the work being done. So besides the lag, it’s can also be affected by other factors. So trying to stock to a set number can be dangerous too.
My comment on THHR decay comes from an activity in the Fall or late Summer where I think I remember seeing a notification that my THHR had increased to 156.
Yesterday’s activity said my THHR had increased by 1 to 154 so I assume, my THHR had decayed from 156 to 153 and is now 154.
Is this because in my current training I’m not pushing hard enough?
I’m actually trying to manage intensity and avoid unproductive stress
Other than 1 obviously unstructured race per week, I do a 2-3 hour zone 2 , a 3X10 SST, AND 4 X 2 min 120% FTP.
The only structured ride that would touch on that energy system is the SST intervals and by definition, I’m just at about 90% THHR (90% FTP - are they the same).
I’m happy with my training, I’m showing less second half and late race fade and that was my training goal this Winter.
Just not sure if I should incorporate THHR somehow or just use it as a marker.
HR zones and power zones don’t always overlap as neatly as some zone calculators might suggest. So 90% THHR may well = 90% FTP for some athletes, on some days, at some points of their workout. At other times, it won’t. For some athletes, maybe it never will.
I wouldn’t worry about the small changes that are being suggested to you by intervals (or elsewhere). There is going to be day to variance in your threshold HR (even intraday variation): for example, if you repeated that same 18 min climb three times back to back “at threshold” you would get different results.
Use it as a guide / marker, with power and RPE.
If the things you are training for call for extensive periods at threshold (time trials for instance), then you might incorporate more such work in your training. Being able to dial in to a threshold effort is certainly a benefit in such events.
Rather than trying to work at a specific HR marker, you could consider building some progression into your SST and 120%FTP work. For example, an SST progression might go from 3x10 to 3x12 to 3x15 to 3x20. The 4x2 @120 might go 4x3, 4x4… or it might go 4x2 @120% to @123% to @126% to @130%
What that does to your reported threshold HR might be slightly interesting to note, but increasing it isn’t something to specifically target imo.