Huge gains in LTHR - legitimate or error?

Hi all, I’m 1 year into cycling and have been using sufferfest for the past 3 months. I’ve seen some great gains in my FTP since using sufferfest (~15% FTP increase, ~18% MAP increase), but today I did a HM test and my LTHR was super high! If it’s accurate then I will be super chuffed, but I’m wondering what the chances of error is in HM and 4DP for LTHR? Below info for full context:

  • 4DP on 15 May 2019 - LTHR of 168 detected (~88.4% HRmax). Felt fresh.
  • 4DP on 29 June 2019 - LTHR of 164 detected (~86.3% HRmax). Was carrying some fatigue.
  • HM on 12 August 2019 - LTHR of 175 detected (~92.1% HRmax). Testing after 3 full days complete rest/inactivity.
  • the past 6 weeks since last test I have been training very hard, a lot of time spent at racing intensity sitting in high heart rate zones. Every week I have reached or been within 2 beats of HRmax.

Has anyone had similar LTHR improvements? Is my improvement legitimate or potentially an error?

Hi there. HR is so variable vs Power it’s hard to say.

Fully rested before a test, irrespective of HM or FF or anything else for that matter will allow you to work harder. And the harder you work the faster your heart will beat to keep up.
FWIW - but we’ll be different ages, different hearts and lungs and so on, I typically see LTHR of 163-168 (vs tested max of 175) during tests (so 93-96%). But again it’s all down to how our own bodies work as individuals, how far we push testing … could I get another 1-2 on to my max, who knows … did I sleep well … etc etc.

((One thing to watch out for … “HR improvements” isn’t the ideal term maybe - though I guess you could be working harder as you get more and more used to this kind of regime and getting used to having your HR up high?))

Ps when testing if my own HR is lower than those numbers I know I’m not working to my best … For one of the many many reasons all listed in one of the articles, be it sleep, nutrition, fatigue, life stresses, etc etc.
Those ones I tend to complete anyway, but I don’t log as relevant tests for me.

Hey James,

Go back and see what your peak heart rate, and peak 1minute heart rate were in Full Frontal. If your peaks from Half Monty and Full Frontal are the same, then keep your existing LTHR setting. If your peak heart rate was more than 10 beats higher during HM than FF, I would suggest splitting the difference between the new recommended LTHR, and the FF set LTHR.

Also, has your heart rate been higher than the target heart rates on most of the workouts? Heart rate is tricky as it is impacted by so many variables. It’s possible your heart rate was abnormally low when you tested FF, or that it was abnormally high when you tested on your last round.

I hope that helps, and it would be great to hear your answers!


I hope it’s ok if I am hijacking this thread a little bit.

I am reading and rereading THIS article here on LTHR and somehow I have a knot in my head.

Why is a higher LTHR a gain? Why is a bigger number better?

I mean, of course, up to a certain degree I am able to push myself to go faster and/or more powerful but at the same time consistent endurance training is lowering my resting heart rate and the heart rate my body needs to uphold a certain performance level.

Let’s say, theoretically, my 4DP numbers during two FF stay exactly the same but my LTHR goes up, doesn’t that mean I had a harder time doing it and are not as “fit” as I was? Of course concidering same stress, rest, nutrition, everything…

Doesn’t it need to be put into perspective with the overall gains, too?

Sorry if this is a dumb question. Maybe I am overthinking this.

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Hey Coach! thanks for the reply. OK so below are my previous HR metrics:

  • FF test 1 - HRmax 184, LTHR 168
  • FF test 2 - HRmax 180, LTHR 164
  • HM test 3 - HRmax 190, LTHR 175

Re: target heart rates - I have recently noticed that yes, my heart rate is at the higher end or above the target heart rate. Previously it was always at the lower end or below the target heart rate.

Some other points which may be of interest:

  • My Garmin estimates my LTHR at 172 - 174bpm
  • I am 100% confident in the FTP and MAP power numbers achieved in HM because they are within 1W of my Garmin FTP estimate and 5min power curve (respectively) - My 2x FF tests and HM test today have produced power numbers that are within 1W of my Garmin power numbers

G’day! Good question. A higher LTHR means one can perform aerobically at a higher percentage of their HRmax before producing lactate/hydrogen ions that limit muscle function. It is an indicator of aerobic fitness that can be trained and improved. The closer your LTHR is to your MaxHR, the longer you can sustain high aerobic performance before the muscles become acidic from production of hydrogen ions.


Sorry, I didn’t respond to all of your questions.

Your lower resting heart rate is an indicator of your VO2max, not related to your LTHR. ie VO2max estimate = 15.3 x HRmax / resting HR.

All things being exactly equal (stress, nutrition, sleep), one should not see two tests with the exact same power numbers but a higher LTHR. All things being exactly equal, one could expect to see increase in both, or a decrease in LTHR.

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Thanks for the extra info @jamesrandles. So if we look at your most recent results:

  • FF test 2 - HRmax 180, LTHR 164
  • HM test 3 - HRmax 190, LTHR 175

You have that difference of 10bpm on your max HR so if you add half the difference of the LTHR that puts you at 170.

The heart is a muscle and with training, it gets more efficient at pumping oxygenated blood around the body and clearing de-oxygenated blood back to the lungs. So @Pierre, a higher LTHR means that your body can function efficiently up to a higher level of strain.