I suggest using this tool to calculate your training zones

1. Above is your basic problem. Do a ramp test (e.g. like the one implemented in Zwift) and you'll know your real max HR. I guess it's a bit higher than what you've been thinking.

2. Then, I recommend to setup HR zones using HRR% (e.g. Z2 being Resting HR + 60-70% * (max HR - Resting HR)).

3. Think of your zones as a range, not exact numbers. Depending on individual days, hydration, mental state, fatigue etc. you'll be somewhere in the range.

4. If you want real physiological zones, and not estimated ones, do a metabolic lab test.

I see two things-
1.) You are describing the zones as a number rather than a range. This is a big mistake.
2.) If FTP is 255 and 165 takes you to Z4 HR, FTP is likely incorrect. How did you arrive at this FTP number? My guess is that you need a longer test/effort to properly pinpoint FTP.

Some very good info above. I'll add the following:

-Max heart rate is somewhat irrelevant, estimated max heart rate is completely irrelevant. Lactate Threshold heart rate is fairly important but also fairly variable. A ramp test is a good starting point to find an estimate of FTP. If you're newer to training your sustainable power is going to go up at a higher rate than your sustainable HR.

-Unless you have a really good idea of what you're trying to do in a session it's usually best to just go by power. Say you're supposed to do a 4hr Z2 ride. In all likelihood, even with correct HR zones, you'll start to drift out of Z2 by the end of the ride. I'd argue against dropping power to stay in the right HR zone, that is divergent from basically any racing situation you'll encounter. Races are won by speed, speed comes from power, power comes from metabolism (HR). It's sometimes good to break things down to components but never forget the actual goal (going faster).

-A good practical way to find HR zones is to do an FTP test, use those zones and just pay attention to your HR during steady state stuff. Doesn't take more than a few weeks to get a good idea of whats normal for you.

Not to hijack this thread, but I have a similar problem. And, to add to it - my "true" LT2 is about 50-60 watts lower than my FTP based on taking 95% of a 20-min max effort. Does anyone have advice for how to close this gap? Should I just ignore FTP and treat my LT2 as my FTP?

I would go with one or the other. Not both.

The one I chose would be from testing and not a theoretical one. For example, using the 220- age calc for HR I should only be able to get my HR up to 165 but in practice I can get over 180.

If I was going by HR I would do the last 20 min of a 30 min run test.

Yes this is fairly common when comparing 20min/ramp test to blood test LT2. 50-60 is a big divergence.

Can you actually maintain this FTP (95% of 20min) value for 1hr? Most people can't
How are you arriving at LT2? A ramp test, 5 min intervals, 20 min intervals, just 2.8/4.0mmol?

If they are actually this divergent it just points to an athlete much more trained for short intervals than long ones. This is pretty common (but not necessarily bad) especially with people coming from Zwift/Peleton/Trainerroad where the preponderance of workouts are 1-5min intervals above LT2 and rarely the 20-40 min stuff tempo type stuff.

Power is the work/effort you are doing, hr is the body's response to that effort. Power modulates HR not the other way around. If you want to lower your HR you reduce power. Increase your HR increase power.

i think knowing your zones is less important than most think it is.

Knowing when you're near/at/above threshold aka that point which under it you can sustain working hard for a long period of time (45,58, 84 minutes to just choose #s) is possible where as if you go over it the duration you can sustain it might only be 5, 13 or 17 minutes.

Without knowing how you determined your ftp, giving you specific # is really hard.

Quite often (most often) ramp tests, especially short duration ramps, give you a # that is higher than you can sustain for an extended duration of time, say 45-90 minutes.

If you did a straight 20 min test that also will often give you a # too high. You may be able to sustain that for 30 maybe 40 minutes but I doubt much beyond that. That might be ok for you to work off of, especially if you can sustain that for 40-45min but not 55-75, or it may not.

If you did the 5min all out previous to it, then the 20 you can have more confidence in the number yet it's still not foolproof.

Hope that helps

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Brian Stover USAT LII
Accelerate3 Coaching
Insta

So, if we hypothetically assume my FTP is correct.......and say I want to do my Ironman bike in 'zone 2', do I keep it in Z2 of HR, or Z2 of power??

In the race do it at the effort you can maintain that will allow you to run well. use both. In fact I often tell my athletes to use their brain (PRE), power & Hr concurrently to insure they are racing smart and training effectively.

Since you are using power you can look back at your data from rides that are +/- an hour of your expected IM bike split and see what power you held for those. Why would you constrain yourself to an arbitrary metric that fluctuates day by day? For instance you may be able to ride zn2 at 125hr in Seattle. but if you come to Tucson right now you'll probably be 10-15 beats higher bc it's hot and your power might even be lower as well.

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Brian Stover USAT LII
Accelerate3 Coaching
Insta

what predicts ironman performance the best....simulating is as closely as possible and an FTP test is pretty far from that metric

SBRcanuck wrote:

I'm a little confused as to which to use, HR or power, for zone training on the bike.

Good question. I wrote about that here in a newsletter.

In a nutshell, your decision on what to target for your session should depend on the context. Ask yourself => What am I trying to achieve? Heart rate is valuable for longer duration exercises, such as Zone 2 training or sessions involving hills, altitude, or heat, as it reflects internal stress and factors like hydration and training fatigue. The purpose of <Z2 sessions is to develop your aerobic fat burning engine. So for these, follow HR and let power just be.

On the other hand, power is useful for shorter key high-intensity sessions at or above threshold intensity. In these cases, monitoring heart rate can be done later.

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https://athletica.ai/
https://hiitscience.com/

You should probably call Lionel!!

I'm first on the waiting list for his coaching services, platinum package!!

I suggest to use both,

for short intervals, always use Power.

for threeshold intervals use power to start, but check that the HR will not go higher

for aerobic use a combination of HR and Power. You could (for example), use power in Z2 until your HR is in place, and rest in Z2 low or Z1 high to mantain HR in zone. Your objective should be that Z2 power and HR match.

your objective is not to "be able to sustain Z2 power during 180km" but also to do it in Aerobic zone (= HR Z2)