I’ve increased my volume recently, mainly on Zwift as we’ve had a wet, chilly spring and I moved last fall, not sure of the good routes around.
My Resting HR is showing at 46 when I haven’t been below 50 in a long time, and in a Zwift race yesterday my HR was way low.
Maxed at 140 with a 6min max effort climb at the end. Recent high HR is 179 in March, 189 in January, hit 174 10 days ago.
I’m hitting (recent) power bests in a variety of durations while this is happening.
I’d write it off as equipment completely except that I’m looking at consistent numbers across my Garmin watch optical sensor on wrist, Garmin chest strap, and polar optical sensor on my upper arm. I’m suspicious of the Garmin chest strap as I think it may be on its last legs so will probably try to dual-record HR on my next ride.
If it’s not equipment, what could it be? I’ve never heard of such a thing before.
Mind sharing a screenshot of your Fitness page? That might give us a bit more context.
Also, just to confirm – did I understand correctly that the HR drop happened literally from one day to the next?
I’d say the resting HR drop was to 46 after having been consistently 50-60, but when I look back those drops have happened before. It’s probably been gradual that my max efforts have been going down over the past couple of months, but I’m just not getting high HR at effort. I was 174 in a Zwift race on Saturday that was very “surge and recover”, then 141 max in a Zwift race Monday that finished with a 6min max effort that gave me a 1W eFTP increase. And I felt like utter crap in that race, I didn’t feel warmed up at any point.
Last 6 months fitness chart is below. I use 6 months because I was seeing HRmax of 189 in January. I think the time high I’ve ever observed was 194 when I first tried a HRM running in 2007. I’m going back to my old pre- Garmin Connect data to see.
I agree - When I say consistent I just mean that I’ve been seeing similar numbers for similar rides when I switched between. The Garmin wrist HR I’ve found has always clipped the highest values, but tracked decently at lower values. I haven’t dual-recorded with them yet. Plan to record with two devices today, I got a new Garmin strap as I was suspicious of the old one. Yesterday was an early morning ride, today is evening.
yeah… that’s fine. Since you’re not really looking at exact seconds-to-second comparison. Just looking at roughly how much they differ at any point in time. shouldn’t be more than couple beats
In general regarding RHR – I assume you’re tracking it overnight using the Garmin smartwatch, and not doing a dedicated morning measurement, right?
I’ve also seen outliers of 10–20 BPM myself, which I’m pretty certain were just overnight measurement errors by the watch…
Just throwing that into the mix – although it is strange if it happens exactly at times when you also can’t hit higher heart rates during training.
Yeah, that’s a shame – you’re probably right, the FR735 doesn’t record HRV on it’s own optically as far as I know…
But a long-term RHR graph would still be interesting!
Its happened to me several times when I was self-coaching, on surprisingly lower hours/week but high intensity efforts and high stress at home and work. For example HR wouldn’t go above 150bpm on really hard group rides when it would normally be 130-175bpm.
Thanks - I’ve always had elevated RHR as I’ve approached overtraining before, or actual decreased performance, not low HR at recent-best performances.
It’s certainly possible. Sure looks like it isn’t equipment after my ride tonight. Old chest strap and new Garmin HRM-Pro tracked exactly.
There is a lot of activity in the winter that doesn’t get captured in my log (curling, snow clearing, etc.) so the bump this spring isn’t as big as it looks on the graph - but it’s definitely more cycling than I’ve been doing, and fewer days off.
No, not all all. I think you’re likely correct, but I have never had low HR during exercise show up as a symptom when I approached overtraining before. Or had ever heard of it.
I’ll try to take it easy for a week or two. Last night’s mostly-easy ride (after easy ride Tuesday morning to Wednesday evening mini-recovery) was higher HR than Monday’s race.
I finally had the time to take a closer look at your data and posts — and gave it some proper thought. I also ran your observations and my take on them by Dr. GPT (our in-house endurance nerd ), and we came to the same conclusion WindWarrior already pointed out — here’s a more detailed breakdown:
What’s likely happening physiologically?
When training volume increases too quickly without adequate recovery, the autonomic nervous system (ANS) can shift into parasympathetic dominance. One hallmark of this state is a blunted heart rate response during effort — you may be hitting power PRs, but your heart rate doesn’t climb like it used to.
Your resting HR drop to 46 might seem like a fitness gain at first glance, but in this context, it may reflect autonomic suppression, not improved conditioning.
Scientific backing:
Meeusen et al. (2013) (European College of Sport Science): “Suppressed HRmax despite unchanged or improved output can be a sign of functional overreaching.”
→ DOI: 10.1080/17461391.2012.730061
Halson & Jeukendrup (2004): Found early overtraining signs include lower HRmax, especially in high-volume HIT blocks.
→ Scand J Med Sci Sports
What your chart says
Fatigue > Fitness for weeks = accumulating load
Form ofte in the High Risk zone in May
Resting HR drop + low HR during max efforts = suppressed cardiac response
Yet still hitting new power records → classic functional overreaching territory
What could help:
4–6 days of low intensity or rest (your nervous system needs a break)
HRV would be really useful to confirm this — but unfortunately you don’t have a device for that. Too bad — those would be interesting numbers right now.
Prioritize sleep, nutrition, magnesium, vitamin D
Consider a field test or ramp protocol to confirm blunted HR response if you’re curious
Conclusion
Based on your consistent HR sensor results and training history, this strongly points to physiological overreaching, not faulty equipment. You’re in the grey zone between peak performance and overload. A small reset now will likely restore your HR dynamics and leave you fitter long-term.
Great riding — smart to question the data instead of pushing blindly.
), and we came to the same conclusion WindWarrior already pointed out — here’s a more detailed breakdown:
What’s likely happening physiologically?
Scientific backing:
What your chart says
What could help:
Conclusion