How to Calculate Threshold Heart Rate

Training and Performance Fundamentals
1

New TD user but not new to structured training :slight_smile:

I’ve mainly used power for zones but I’ve grown a bit more curious on monitoring HR for longer zone work and also to assess how my body is reacting to certain power zones - especially when recovering from illness.

In settings, TD asks for “Threshold Heart Rate” - asking you to look for a 20 minute “all-out” effort. Easy way to do this for me is to look at the HR curve in my Intervals.icu account and take note of my highest sustained HR for 20min in the past 42 days.

So here goes my stab at figuring out threshold HR.

Current age: 49
Highest sustained HR for 20 min in the past 6 weeks: 170

Using the 5% above max 20min hr, that would put my threshold HR at 179 which is right at my highest documented hr in recent training.

If I take 80% of my max (179) (the “other” way to get a threshold HR), that puts me at 143bpm - which seems low as that’s about where I sit for some Z2 rides.

Another point of reference…

At a recent 67 mile gravel race (3100’ elevation gain) where I ended up 6th overall, I averaged 158bpm for 3hr 41m with a max recorded HR of 176. Efforts were a mix of “OMG I don’t think I can hang on” to sitting up with the front group that didn’t want to do any work :slight_smile: In the end, 3 of us pulled off the front group to come in P4/5/6 together. Was my best-ever finish in a proper gravel race. Taught me a lot about working smarter, not harder - was able to do this with a modest 3.5 w/kg ftp.

So, back to the initial question - how the heck do I come up with a threshold HR? :slight_smile:

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Joe Friel’s protocol is to do a 30 minute time trial and take the average HR over the last 20 minutes as threshold HR.

The average of the full 30 minutes can be used as your FTP power.

Dave

3

Wow, 6th, cool. I am dreaming of my first gravel race, likely next year. But my first will be pretty flat…

Anyway, if you look at the 5% it would be 5% less not 5% more… you calculated backwards there. That puts you at 161 which compared to your 158 for 4 hours sounds pretty close. I like Daves answer on Joe Friels test as well.

Most people won’t hit a max HR in a long event. My bet is your max HR is closer to 180-182 if you did a max HR (3 all out sprints after a good warmup) test but that is just a total guess. So because you can sustain such a high percent for 4 hours I would say you are very aerobically fit or your HR max is higher than you think and you are still aerobically fit :slight_smile:

So I would use 161, but it’s possible its a bit higher than that. 158 4 hours 161 for 60 minutes is very tight but since you have a very high threshold the numbers do get much tighter. If your max HR was a bit higher than you think I might think your threshold could be between 163-165…

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Thanks Dave. That 20min example was from a hill climb time trial. Still, I’m not sure I’d want to set 170 as my threshold hr! But what do I know?! :slight_smile:

5

Interesting. Interval.icu had this comment on that particular ride:

" Threshold HR +5 to 167 bpm from 98% of 20m at 170 bpm " So wow, maybe the truth is somewhere in the middle of yours and Alex’s posts! Thanks for the help!

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Ah! Thanks Alex, yep the TrainerDay app says to “Take that number and ADD 5%” so that was throwing me off. Thanks for the clarification.

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Oh and I checked my past rides since May of 2023 and my max that I’ve hit is 179bpm.

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And just to add to my own “noise”, I did a 2x12 Threshold effort last night and at the end of my second effort I was right at 168. So, sounds like we’re getting close!

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Oh no!!! :slight_smile: Need to fix that.

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So that might be your max but without this warmup and 3 max efforts with short rests between you still might not have actually reached your max. Some people have said you almost never hit your max it’s probably always 5 above what you see in a workout. But if you are curious try the 20 minute warmup followed by 3 X 1 minute sprints each one to failure. The third one should show your max. Might be easiest on the trainer in slope mode but outdoors is fine as well if you have a good spot to do it.

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Threshold heart rate, or LTHR, is supposed to be your heart rate that is at the dividing line of stable and unstable physiology.

I’ve done the 30 minute test and my result was 169 BPM. My max cycling HR observed in the last year is 191 BPM. I don’t think my LTHR being 88% of my cycling HR is out of line.

Training Peaks link: Joe Friel's Quick Guide to Setting Zones | TrainingPeaks

The difference between stable and unstable physiology I think is very key here. I would NOT use as 5% adder and would instead use the 20 minute result.

Dave

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I agree 88% just indicates solid aerobic capacity and might have a genetic component. Yes adding 5% was mistake it should be subtract or last 20 of 30 seems like it should be similar. Personally I would be fine with the accuracy of highest 20m avg as well.

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I haven’t done any lactate testing but what I understand all of this is really intended to do is to find your heart rate at mean lactate steady state (MLSS) which if I understand correctly 4 is typically mM give or take.

Personally, while it is good to know what LTHR is I don’t know how to use that data effectively. I guess if I were to be doing threshold intervals like the 2x12 and I didn’t reach LTHR then maybe my FTP has gone up or I’ve over-trained and if I went over LTHR then maybe my FTP has gone down or the air flow is too low, it’s too hot, I have off the bike stress, etc…

The reason I did the 30-minute is because it is a lesser evil FTP test. I find the 20-minute test is very difficult when you include the 5 minute blow out period before it and the ramp test for me is not accurate, there is way too much anaerobic component. The 30-minute result seems to be something I can actually use for setting training intervals.

Friel has another test, a FTP verification test, that uses LTHR along with 4 minute work/1 minute recovery steps to confirm FTP. This could be used instead of the 30 minute test because it hurts less and is still reasonably accurate. The idea is that FTP will still occur at LTHR when it goes up and down.

https://www.trainingbible.com/joesblog/2008/08/ftp-confirmation-test.html

Dave

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Yes, for the training style we recommend aboslute accuracy is less critical. Coach Jack starts easy and eases you into hard stuff so most people will adapt to it at the speed it progresses. If you are following more of the TrainerRoad style of sustained sweet spot or what I consider worse starting with 4x10 or 2X20 threshold workouts or something accuracy becomes much more important (that it’s not too high) to reduce the suffering or increase the chance of survival.

So for me last year my ramp tests were like 230 watts and I am sure my FTP was closer to 200watts. I also have a strong anaerobic component. But I guess since I know this I just adjust it down to 200 and it is close enough from a training perspective (Coach Jack suggested style).

So the great advantage of a ramp test is that it tends to be more consistent as many people blow 20 minute tests with poor pacing. Not to mention the suffering so most will rarely do it.

I don’t understand though. Why is a 30 minute easier than a 20 minute? My mind is kind of shot so I don’t fully understand what Joe is saying there but I was thinking a longer ramp FTP test would remove more of the anaerobic component.

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If you do the 20 minute test “right” per Hunter Allen you have a 5 minute blow out period followed by a recovery before you start the 20 minutes. The 5 minutes is supposed to be all out so your anaerobic stores are used up.

I think that hurts more than 30 minutes at threshold. I’m not a huge fan of the 30 minute test either, so honestly I’ve been using a “triangulated” FTP and going by feel.

Dave

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Oh right I forgot about that one, I was trying to understand what you were saying but I forgot about that. That test makes a lot of sense.

In the old days in TR I and other platforms it was the 2 X 20 that I used to do (also ugly). Once I switched to ramp test I never went back and revisited these painful tests. Yes, triangulation is good. I have need to do something soon and in reality I should do a 20 to 30 minute test but I will likely do a ramp test instead :slight_smile: Unless maybe I do it outdoors which sounds more fun if I could find a good place to do it.

I was working on FTP estimates based on computational triangulation including HR/power ratio but I could barely make it accurate for myself so got burned out on it before I completed it. I don’t think anyone has done triangulation “AI FTP detection” like I think it should be done. When I can find the right smart enough / excited enough programmer to work with me on this I really want to. Maybe now with LLM based programming it might help solve my problems.

17

Ah, these are interesting topics. Let’s start with why, in my opinion, you can never just use power, and heart rate is still important.

There is a difference in your performance output and its impact on your body.
Power measures the output and heart rate measures the effect of that output on the body.
Since many more external factors (such as temperature, time of day, etc.) and interval factors (such as hydration, core temperature, length of the training, etc.) influence heart rate, it is not ideal for measuring intensity.
It is, however, essential to see how the body is coping with all the stress while performing.

So, in general, I recommend using power to guide the intensity of your training and heart rate to check on your progress.

We always expect to deliver the same FTP every training session, but let me tell you firsthand that after three days of hard training, even my recovery workout yesterday was a pain.

That being said, how do you set your training zones for heart rate? The only right way to do this is to measure lactate for both aerobic and anaerobic thresholds.

But since this is a costly test, you can also use max heart rate to calculate this. Or, as you already discussed, use a 20—or 30-minute field test. The downside of a 20—or 30-minute field test is that external factors play a big role again—much more than with a max heart rate test.

Never perform a max heart rate test without knowing that you are healthy. Although this test is short, the impact on the heart is high.
If you are already in your forties and up, I would seek out a doctor and ask his/ her advice if this is healthy.

The thing with these test are the outcome is only temporary. After four weeks of dedicated training the values can go up and after two weeks of rest the have gone down.

If you are consistent with your schedule over time, you will see that these thresholds move within a range.

The thresholds are also connected. Do a lot of aerobic work, and not only will your aerobic threshold go up, but your anaerobic threshold will go down, too, and vice versa.

The more data you gather, the better you will understand your body. For instance, it can be beneficial to do a test indoors and one outdoors, from the perspective of temperature.
You will see that there is a difference.

In the end, there are different tests that measure the same outcome. They all have pros and cons. Do the test, use the outcome in a training session, and decide if that result is valid for your training.

Finally, stick with one test that works best for you. And occasionally, let yourself be tested by a pro.

Have lots of fun

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18

So yes, max HR tests are a bit risky, and per minute of time potentially more risky than 99% efforts but it would seem minimally so from my research. Do you have any studies pointing out that 100% is more risky than what many athletes hit regularly of 97%+ ?

From all my reading it seems that duration plays a big role in heart risk when talking about intensity. So low intensity is safest, everyone should be sticking to Zone 2 :slight_smile: But for those of us that like how we feel when we do more intensity and willing to take the associated risks, I believe the risk focus shoudl be on the combination of intensity and duration. But sure, everyone doing intense exercise should check with a doctor.

FYI - Here is what GPT says

GPT: For generally healthy individuals, especially those under 35 and without known heart disease, the risk of a cardiac event during intense exercise (including MHR testing) is extremely low. The incidence rate is estimated to be around 1 in 50,000 to 1 in 100,000 hours of exercise.

GPT: The risk increases with age, particularly for those over 35, due to the higher prevalence of underlying cardiovascular disease. The risk during vigorous exercise for this group is estimated to be about 1 in 15,000 to 1 in 50,000 hours of exercise.

Alex: So intense exercise is more risking for a cardiac event than driving a car is for a serious accident this would not stop me.

So play it safe and stick to zone 2 :slight_smile:

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