AF Association
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Low heart rate after exercising more

Hi all,

Haven't posted here for a very long time, hope you are all doing well!

For over a month now I've been keeping myself fit by going out running, sometimes for long distances. On average I probably go running once every two days but there's been some times where I've ran every day or even multiple times in a day.

I've definitely felt myself becoming fitter, but there is something that is some cause for concern.

My resting heart rate has come down quite a lot. Earlier today for example, I measured it at 43bpm, which is pretty low.

I was wondering whether you all thought this was cause for concern at all. I don't have any other symptoms, and I'm not on any regular medication. Anyone else have any similar experiences?

Thanks,

Mike

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I was and to a lesser extent still am a cardio bunny. Before I was on medication my daytime resting heart rate was around 45. Whilst sleeping it would drop to the mid-20s and pause for 2 to 4 seconds. For that reason I couldn't take beta blockers and, a specific medical note had to be made if I was undergoing general anaesthetic as my blood pressure would be low during recovery. I was away from exercise after a stroke a year ago, but I'm introducing cardio again. Given your short history of exercising I wonder whether you are overtraining and your low heart rate is in part a parasympathetic response.

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Training will reduce heart rate so if you are fit then this is not overly low. I have often come across athletes with lower rates. If you are worried then speak to your doctor.

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Agree Bob. When I was a runner my resting heart rate was mid 40's.

Don't run anymore, but now mid 60's. I couldn't tolerate betablockers because they dropped it down again, and not because I was cardiovascularly fit, just drugged.

Talk to your doc.

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Does your heart rate bother you physically - dizziness, feeling faint or wobbly - or do you feel fine and are just concerned about the figures you are getting?

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You don't mention what your HR was before you started exercise, and your post implies that you have only been running for a month, is that correct? What level of exercise were you doing previously?

BobD is right, training will reduce your HR, and 43 is not uncommon for fit people who train regularly, but if your HR was a normal 60ish as recently as a month ago then that is a big drop in such a short space of time. If you're running long distances and multiple sessions in a day so soon after starting my bet is that John-Boy is right, and you are seriously overtraining. Abnormal drops or increases in resting HR are an indicator of overtraining.

To increase your fitness by training you have to show your body that it's not currently fit enough by pushing yourself a little beyond what you're comfortable with. That excess will create fatigue, and then when you rest your body responds to the fatigue by increasing your fitness to accommodate the extra exercise you're doing. If you don't exercise hard enough to induce the fatigue then your body will assume it's fit enough for what you need, and won't get any fitter, but here's the important bit: you MUST let your body recover from the fatigue of one session before starting another. If you aren't recovering in between training sessions, then the fatigue will just accumulate, and you will descend into chronic fatigue and exhaustion. Failure to recover can be either due to too little recovery time, or too much exercise in one session, (or both), and too much exercise can be either too much volume or too high a HR.

Overtraining can be insidious, because it often appears that you are making huge leaps in fitness at first, before the fatigue sets in. It's quite common to feel temporarily as if you could run forever after an excessive session, and then for it to quickly wear off, but if you respond to that by getting more exercise rather than less, that's a recipe for disaster. The danger with overtraining is that if you accumulate a sufficient level of fatigue, and then maintain it for a protracted period of time, you can reach a point where it's impossible to recover at all, no matter how long you rest. When that happens it's known as overtraining syndrome.

My recommendation would be that you find one of the many training schedules that are published, and follow it. Typically they start with around 30 minutes at about 60% of MHR three or four sessions a week, and then build up at about 8-10% per week from there.

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Hi there,

Thank you so much for your detailed response, it's been very helpful.

I think your analysis is pretty spot on. I'm going to try and give myself sufficient rest periods from now on and train more sensibly.

Note that I took the 43bpm hr reading just before bed when I was lying down, and before I started training to the extent I am now, my resting hr was still fairly low in the low to mid 50s, so still a big drop but not as significant as if it were in the 60s or 70s. I've been fit and exercising to varying degrees most of my life.

Thanks,

Mike

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I measure my RHR first thing in the morning before I get out of bed, which I think is the conventional way to do it. Mine's still about 42-47 after six years of rest, with no sign of recovery, and little prospect of resuming training yet.

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Interesting, I used to train and swim all the time and was in the air cadets for a while so fitness was a big part of my life. Do you think my low heart rate may have something to do with that?

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If HR has been driven low from training I don't really know how reversible it is with rest. I don't really mind what my HR itself is, I just want to be able to exercise again.

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You just sound pretty fit! How does it compare with pre AF?

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My RHR was 38 this morning.

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The r - r interval of your heart beat can be a good indication of whether you should rest or train. The Ithlete App will measure the r - r interval in conjunction with a heart monitor chest strap. The problem is that AF can cause an error flag. In the week before my stroke, Ithlete showed an error every day although my blood pressure monitor (with AF detection) and the pleth display on my oximeter showed nothing untoward. I've just bought a Concept 2 rowing machine and given the 5km row most days, I need to start using Ithlete again and recording resting heart rate and blood pressure.

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