Can't reach and sustain LTHR

Hi guys,

I am 47 a CX and MTB XC racer. I have just completed a large block of training and have given my self 2 easy weeks. My max heart rate is 179 but can currently not get it over 170 without blowing up. Mt LTHR is around 174, My FTP is 321 but struggle to hold this. Am I over training / under recovering or could I have a viral infection.

Any one else experienced this?

How did you determine your LTHR if couldn’t sustain it? LTHR is best found from a 30 min all out effort avged over the last 20 mins

Others may correct me, but a threshold that’s 97% of your maximum sounds off. I’d say one of those numbers is wrong. How did you test or calculate them?


LTHR measured during FTP test

If you know your max is 179, I seriously doubt your LTHR is 174.

To answer your question, at 41, my max HR on a bike right now is 191, and I have to bury myself to go much above 178 for any length of time, and at this point, when I’m that high, it’s probably my muscles giving out because I’m up well above threshold or I’m above threshold and have been there for a while. So to answer your question: yes, I experience similar things. I don’t think that’s abnormal, and it’s likely that your legs are limiting your ability to raise your HR any higher.

That said, I would suggest that you need to re-test your LTHR (or perhaps your max HR).

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Which test, specifically? 20-in? 8-min? Ramp?


When I race CX for 1 hr my average HR is between 170 - 173

A ramp test isn’t a good measure for LTHR. It’s probably a decent way to find your max HR if you really, truly bury yourself until you just can’t pedal anymore due to cardiovascular fatigue (not muscular fatigue). For most of us who are trained, our legs give out first.

As @redlude97 said, LTHR is usually tested over a much longer, sustained effort. A common protocol being a 30-min max sustained (and well-paced) effort, with LTHR being the average over the final 20 mins of that effort.

I’m not a CX racer, but based on my experiences as a runner, I would expect your avg HR during CX events to be somewhat higher than a sustained cycling effort due to the additional stress of mount/dismount/carry and running, all at high effort levels. E.g., my tested LTHR on a running track is about 7bpm higher than a similar test on a bike trainer, so for me, running at 170bpm and cycling at 170bpm feel a hell of a lot different!


My lthr is 193 and I avg over 205 for 45 min CX races. They arent the same. A lot more upper body movement, discounts and running as well as a highly variable effort.

I’m trying to look back at my log from last tri season, but I think my tested running LTHR was 178, and my bike LTHR was 171, both off of max HRs in the 190s. I haven’t tested this year, but I can sustain in the neighborhood of 170bpm for quite a while on the bike.

If 179bpm is truly your max, I’d expect your LTHR to be closer to 160 than 170.

#1. Your max HR is probably wrong, given the other info you’ve supplied.

#2. You are probably fatigued if you aren’t able to hold a threshold effort for a reasonable period of time (15-20 minutes) and HR stays depressed

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