28-year-old with a resting bpm of 57 - too low?

[Victoria044]

Hi there. 

I'm 28 years old and in the past month have lost about 6lbs (steadily, eating right and getting my steps in through walking 10,000 steps most days).

I now weigh 136lbs but have noticed that my resting heart rate, which used to be around the 70bpm mark, is now 57, dropping almost a beat per day over the past few days... I'm wondering if that's normal?! Is it just the loss of weight causing it? I'm definitely not an athlete (i have a sedentary job, work from home, and go for a (very slow!) swim maybe twice/three times a week). 

Does anyone have any ideas?

Thanks in advance!

[MarciM]

Hi @Victoria044 Welcome to the forum and congrats on your weight loss. A resting heart rate of 57 is good, not to low at all. Most of us that have been running  for years have resting heart rates in the 50 or even lower, it's sign of fitness level. Nothing to worry about, but to learn more about RHR you might want to read this THREAD.

[Hillymum]

I'm two weeks shy of turning 47 and my resting heart rate has gone down to 61. It's a sign of fitness. Sounds like you are doing great!

[Baltoscott]

Hi @Victoria044.  Congrats on the weight loss.  I agree with @Hillymum and @MarciM that a RHR of 57 is a good thing, but I can see why you could be curious about a seemingly sudden change over what you usually see (70 is in the normal range too).

Here is how fitbit says the calculate RHR:

HOW IS RESTING HEART RATE MEASURED?

Resting heart rate refers to the heart rate measured when you’re awake, calm, comfortable, and have not recently exerted yourself. We use your heart rate data from when you’re awake and asleep to estimate your resting heart rate. For best accuracy, wear your device to sleep. 

Your resting heart rate is usually higher than your heart rate while you are asleep, so don’t be surprised if your resting heart rate is higher than the lowest number that you see in your heart rate graphs.

I don't have any beef with Fitbit using HR data from when I'm sleeping -- one of the great new things about having an all day HR monitor on your wrist is that is makes data available that wasn't measurable in the past.  Still, it is unclear how the sleep HR data figures in to the reported RHR number.  I haven't tried to work it out, but it seems like a change in sleep patterns could affect the RHR number fitbit reports. For example, going from 5 to 7 hours sleep/night might result in a lower RHR number simply because your HR is generally lower while you are sleeping, and increased sleep would likely mean it is lower for a greater portion of the 24 hour day ...

Of course there are reasons unrelated to how FB calculates RHR.  Your decreased weight probably does correlate positively with lower RHR.  Have you noticed any other changes?  Are the steps and swimming you reported an increase over what you were doing before you lost weight?  If so, that would lower it.  Are you drinking less caffeine?  Any changes in medication?  Some folks say their RHR goes up shortly before they get sick.  Mine can move up and down several points over days -- between the high 50s and mid-sixties -- often without any obvious cause for the change, though I tend to be walking or biking more when it is on the lower end.  I've gotten to where I think of anything in that range as within the margin of error for me.  

[USAF-Larry]

Congratulations, @Victoria044, on your weight loss, and your increase your fitness level!  I am in my mid 70's, and my resting heart rate is in the low 50's.   BF (Before Fitbit) and my regular exercise routine, my resting heart rate stayed between 65 and 70, but since improving my fitness level it stays below 55.

[emili]

I am 47 and my RHR is 52. I run, walk, lift weights and eat well. As long as you aren't dizzy or tired or lethargic, confused- you are good to go. Great actually... enjoy your new fitness level...