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42 bpm RHR. Caffeine withdrawal or HIIT?
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I just had my annual health screening and my resting heart rate was 42 bpm. In the past it has almost always been in the mid-50s or so. I'm in good shape, but nothing out of the ordinary for Slowtwitch. I'm trying to figure out what accounts for a pretty significant drop in RHR. (And I don't know, maybe 42 isn't unusual for Slowtwitch?) Two things that are different right now are
  • I have never ingest caffeine regularly until the past year. Work/family things kept me from sleeping as much and I starting using caffeine more and more and I developed a mild addiction (if I don't have about 75 to 100mg in the morning, I get headaches), so I have been slowly reducing my caffeine intake to try to get back to zero. Additionally, since I was fasting for the blood draw, I hadn't had any caffeine that morning and the screening was at 10am. Since caffeine elevates your HR, does lack of caffeine drop it when your body is used to it?
  • I have been doing really intense high-intensity interval training on the bike, taking my heart rate at high as 199bpm and regularly getting it into the upper 180s repeatedly in a workout. I've never done this kind of intensity regularly before. Maybe this has strengthened my heart?
  • I recently re-started swimming regularly, but nothing crazy - 3000 yards 3x per week.
  • Something else?

For context, I'm 40 years old, normally finish about at 10% in races (so in a race of 500 people, I normally end up about 50th), grew up swimming.


Any thoughts?
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Re: 42 bpm RHR. Caffeine withdrawal or HIIT? [nilloc] [ In reply to ]
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I wouldn't be worried. That doesn't seem abnormal.
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Re: 42 bpm RHR. Caffeine withdrawal or HIIT? [nilloc] [ In reply to ]
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Yeah - don't sweat it.

When I was doing IM training (aka - a crapton more than I have the past few years), my RHR was routinely in the high 30's/low 40's.
And I was your age now, back then.

Even now, it's usually in the high 40's/low 50's, and can dip back lower on occasion.

So yes, being more fit in general, is likely why you have a lower RHR now.


float , hammer , and jog

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Re: 42 bpm RHR. Caffeine withdrawal or HIIT? [nilloc] [ In reply to ]
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Similar here. I'm 57 with a RHR in the low forties, although if I'm really relaxed I can dip below 40. I'm occasionally entertained by nurses taking HR/blood pressure via instrumentation, then taking my pulse again manually just to check.
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Re: 42 bpm RHR. Caffeine withdrawal or HIIT? [Murphy'sLaw] [ In reply to ]
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Okay, sounds like I'm not out of the ordinary here. The strange thing is that I don't think of my overall fitness as any better than when my RHR was in the mid- to upper-50s. I'm only training 6 or 7 hours a week right now and am carrying 10lbs more than I'd like. (I know that weight and RHR aren't necessarily related.) The only difference is regular super high-intensity interval bike workouts. The nurse did do a double-take and said that was the lowest he had ever seen.
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Re: 42 bpm RHR. Caffeine withdrawal or HIIT? [nilloc] [ In reply to ]
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At my last annual physical my RHR was 42bpm which caused enough concern (for the doc) that they ran an EKG on me - even though I had given them my history of training levels. I think they are just not used to seeing patients in good health and so when they see low bpm they want to cover their bases and make sure they are not missing something.

I don’t think a low RHR is an issue by itself.
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Re: 42 bpm RHR. Caffeine withdrawal or HIIT? [nilloc] [ In reply to ]
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Like others have said - I wouldnt stress. Mine is always in the low 40s , and I would bet that a majority of the endurance community would also chime in with the same response.
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Re: 42 bpm RHR. Caffeine withdrawal or HIIT? [nilloc] [ In reply to ]
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Like others already posted it’s normal. I am 50 and have a resting HR of 45. Activity level is moderate right now as I am just getting back to a full time training schedule. It’s been a while since I felt overstrained but if I recall my RHR would go up a little (maybe to 50) for a couple of days until recovered.
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Re: 42 bpm RHR. Caffeine withdrawal or HIIT? [nilloc] [ In reply to ]
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Im 33 and my resting right now is 48 when I am not drinking or exercising heavily. I have a friend (in his 20s) that has a RHR of 38.
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Re: 42 bpm RHR. Caffeine withdrawal or HIIT? [nilloc] [ In reply to ]
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Your rhr is not low. Probably where it should be.
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Re: 42 bpm RHR. Caffeine withdrawal or HIIT? [nilloc] [ In reply to ]
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Right now, 41-43 most nights. As fitness builds through the year I’ll drop to 38-39
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Re: 42 bpm RHR. Caffeine withdrawal or HIIT? [nilloc] [ In reply to ]
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nilloc wrote:
I just had my annual health screening and my resting heart rate was 42 bpm. In the past it has almost always been in the mid-50s or so. I'm in good shape, but nothing out of the ordinary for Slowtwitch. I'm trying to figure out what accounts for a pretty significant drop in RHR. (And I don't know, maybe 42 isn't unusual for Slowtwitch?) Two things that are different right now are
  • I have never ingest caffeine regularly until the past year. Work/family things kept me from sleeping as much and I starting using caffeine more and more and I developed a mild addiction (if I don't have about 75 to 100mg in the morning, I get headaches), so I have been slowly reducing my caffeine intake to try to get back to zero. Additionally, since I was fasting for the blood draw, I hadn't had any caffeine that morning and the screening was at 10am. Since caffeine elevates your HR, does lack of caffeine drop it when your body is used to it?
  • I have been doing really intense high-intensity interval training on the bike, taking my heart rate at high as 199bpm and regularly getting it into the upper 180s repeatedly in a workout. I've never done this kind of intensity regularly before. Maybe this has strengthened my heart?
  • I recently re-started swimming regularly, but nothing crazy - 3000 yards 3x per week.
  • Something else?

For context, I'm 40 years old, normally finish about at 10% in races (so in a race of 500 people, I normally end up about 50th), grew up swimming.


Any thoughts?

As other have said 42 is not crazy low in and of itself, but I do not think that is your question. If you have not routinely check it or tracked it and knowing RHR taken from the MD's office yields a great deal of variability, it is likely an appropriate reflection of your current fitness less some morning caffeine.

FWIW, most folks will monitor it overnight or first thing in morning before the java;)

If, by chance, you know it and track it well and it went from the 50's to 42 in a day/week, I would be inclined to get it checked out. It is all about the context of the change. I don't think that is what you are describing, but felt compelled to post just in case.

Cheers.
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Re: 42 bpm RHR. Caffeine withdrawal or HIIT? [ktm520] [ In reply to ]
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Thanks, I didn't want to be a snot (although, this being ST, maybe I shouldn't have worried:), but I was thinking the exact same thing - that nobody was really answering my question. I wasn't asking about 42 bpm being too low, but rather about what would have caused a 25% drop in RHR. Maybe I should have titled the post differently. I rarely check RHR (I only wear HR monitor while working out) so I don't know if it has been going down gradually. Maybe I'll start monitoring it occasionally a little just to have some context for it.


ktm520 wrote:
As other have said 42 is not crazy low in and of itself, but I do not think that is your question. If you have not routinely check it or tracked it and knowing RHR taken from the MD's office yields a great deal of variability, it is likely an appropriate reflection of your current fitness less some morning caffeine.

FWIW, most folks will monitor it overnight or first thing in morning before the java;)

If, by chance, you know it and track it well and it went from the 50's to 42 in a day/week, I would be inclined to get it checked out. It is all about the context of the change. I don't think that is what you are describing, but felt compelled to post just in case.

Cheers.
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