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The fundamental problem I have is that I seem to be incapable of running in zone 2 according to my (Garmin) watch. My maximum (observed) heart rate (MHR) is 175 bpm, and Garmin appears to be just using fixed percentages of my maximum heart rate:

Zone 1:  88-104 (50-60%)
Zone 2: 105-122 (60-70%)
Zone 3: 123-139 (70-80%)
Zone 4: 140-157 (80-90%)
Zone 5: 158+    (> 90%) 

However, I have a low resting heart rate. My sleeping heart rate is around 33-36 bpm, but my resting heart rate while awake is more like high 30s or low 40s, so for the sake of argument I'll take my resting heart rate (RHR) to be 40 bpm.

Yesterday I found out about the Karvonen formula for target heart rate (THR) for a given PERCENTAGE effort:

THR = RHR + PERCENTAGE*(MHR - RHR)

Which gives a very different set of heart rate zones:

Zone 1: 108-120 (50-60%)
Zone 2: 121-134 (60-70%)
Zone 3: 135-147 (70-80%)
Zone 4: 148-162 (80-90%)
Zone 5: 163+    (> 90%) 

So the Karvonen zone 2 largely overlaps with Garmin zone 3, which means that using the Karvonen formula I can run in zone 2.

So my question is, does my low resting heart rate mean that the Garmin method is not appropriate and I should use Karvonen's method (or something else?)?

Additional info: I never seem to get problems with lactic acid when running in Garmin zone 4 and I have had runs where I have run in Garmin zone 5 for over 45 minutes. Both of those things seem inconsistent with the usual textual descriptions of the zones.

Update: Have switched to the Karvonen/HRR approach and have found it difficult to maintain zone 1 when walking and zone 2 using the elliptical trainer. Will hopefully test it when running on Saturday if my Achilles is up to it.

Update: Ran a slow (6:49/km) 10k this morning and had no difficulty keeping to zone 2 (97% of the time). Felt very easy, would not have had a problem holding a conversation, breathing slowly but deeply (in for four strides, out for four strides). Found it easier than zone 2 on the elliptical trainer, but I suppose that just means I am better adapted to running as I do a lot more of that these days. I suppose the question is whether it is cheating to become able to run in zone 2 by changing the formula for computing the zones! ;o)

Update: Ran a zone 3 10k this morning, felt mildly uncomfortable, but could have continued for another hour without difficulty. Not particularly fast (6.09/km) but more enjoyable than zone 2 running. Breathing in for three strides, out for three. Could have held a conversation, but only just. That seems consistent with the usual textual description.

Update: Ran a zone 4 10k yesterday, which felt much more like being at a "threshold" pace than before (5:26/km). Breathing hard (in 2 strides, out for three), would not be able to hold a conversation. Legs beginning to get a bit tired at 7-8km. Again, much more consistent with textual description. Seems like the Karvonen zones may indeed be better for me.

Probably last update: Max effort 5k this morning, 23:58, which was my third fastest time, not bad considering recent injury issues and I did a 3k swim yesterday. In zone 5 for the last 3k, max HR 173. Wanted to rest my hands on my knees at the end, but could stay standing upright, but very out of breath. Again that seems appropriate for zone 5.

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    General advice: breathing out can be one stride longer as it is mostly passive (retraction of the lungs) while breathing in is actively done by the diaphragm (mainly). Helps to fully use your lungs' potential respiratory volume. Aug 28, 2023 at 10:27
  • @PhilipKlöcking thanks, I'll give that a try next time! Aug 28, 2023 at 10:46
  • @PhilipKlöcking gave it a try yesterday, I felt as if I wasn't filling my lungs completely when breathing in, which seems to suggest I can improve my breathing (and that I was breathing too shallowly earlier)? Sep 1, 2023 at 12:20
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    Yeah, may be you could breathe deeper into the abdomen. The main mistake is trying to compensate with the aiding muscles (neck, between ribs) when breathing in. Your shoulders should remain relaxed and low. Sep 1, 2023 at 12:24

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After some comments the conclusion that makes most sense is that this may just be how your body works.

I do have a fairly low resting HR myself (sleep around 40, waking rest around 50-55), am 38 years old and can hit heart rates of 200 when running on or near max with lactate building up or close to the threshold for a while (20+ minutes).

Thus, it may well be that the new formula suits you more, my health app offers several ways to calculate zones. Your data suggests that you found one that fits with your physiology.

That said, 33-36 while asleep is extremely low. Basically, according to my heart physiology lecture, the heart will stop working around 30 because the sinus node will fail.

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  • The 175 figure is about the average maximum heart rate my watch/chest strap records during running each month. Most weeks I do a "race pace" 5k (and occasionally 10k) I'm not sure that is a reliable way of getting the max HR. I'm in my mid 50s, so it is a fair bit higher than the 220-age estimate. I'll mention the sleeping hear rate to my doctor next time I see them. It was 37-38 when I started running last year. Aug 28, 2023 at 10:11
  • @DikranMarsupial What is "race pace" to you? Under 5 min/km? Under 4:30? Under 4? Do you feel able to uphold the pace for any longer or are you completely smashed when you hit your distance goal? For me, I need to stay under 180 to upkeep a good pace and increase my cadence if it goes too high. Just want to point out that the threshold where you start to lactate is not what these formulas mean by maximum HR. It is basically this "close to physiological collapse" line. Aug 28, 2023 at 10:23
  • As I am still new to running, "race pace" has been getting faster, but with similar effort levels. I am currently aiming for under 24 mins (4:48) each week, I generally have to stop when I get to the 5k, but am not at physiological collapse - i can stay standing. I did do a 10k a few months back which I did finish completely smashed, and my heart rate only got up to the low 170s (but was over 165 for most of the run). Aug 28, 2023 at 10:44
  • @DikranMarsupial Edited according to your comments. I am pretty confident that this is just how your body works. Aug 28, 2023 at 12:41
  • cheers! I think I'll keep to the Karvonen HRR formula and not worry that I can't run in zone 2 using the percentage of max HR formula, I think it will be better for my training (especially making threshold sessions taxing rather than merely enjoyable). Aug 28, 2023 at 12:49

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