Any HR expert can explain this?

[jemcp]

I’ve some doubts about either Fitbit HR accuracy or my body tbh.

I’m fairly regular to the gym, 5 weight sessions with 2 hiit treadmill in arms and shoulders day. I’m a male, 33yo, with around 1.72cm, 61kg and ~12/13% bf. In last 4 months I started a diet (15% cal deficit) and dropped 8kg that I genuinely believe was at least 75% fat.

My resting HR is 50 and during hiit, I hit 95% of my HR and I never drop below cardio level even during a 1min resting period. I can hold peak level running for 20mins without a lot of stress since it’s also really easy to get there. I sweat af tho. My HR seems to climb to 120 really easily, either if I walk fast or just do 1 reps. My cardio fitness level in Fitbit is 58-62 but what those numbers really are?  I somehow link the Fat burning with my ability to rise HR too easily but I’m not sure if this is genetics luck or a medical condition. Should I be worried and see a doctor?

[t.parker]

Just as a disclaimer - I am not en expert 😉 Just speaking from my own experience.

In case of any doubts, always see a doctor.

My RHR used to be very low even when I was quite a big person. RHR of 60 wasn't anything unusual for me back then. When I became fit it dropped even further but I can very easy elevate it to the max and drop it while resting. Mind that dropping should occur but it doesn't mean it's going to be instant. Your body is smart. If you are resting during a workout, to drop your HR to the "relaxed" level will take a lot more than just resting. Your brain still expects some effort to be done and it's not efficient to let the HR guard down. It may stay in the higher HR for a while expecting that you will continue exercising (simply, keeping you warmed up). Mind that the way your body works is a very individual thing and mostly observe patterns, not single occurrences. By observing HR patterns I learned how to rest efficiently between sets and looking at those patterns (how HR raises and drops) I can tell a lot about my workout (for example, I can see that even light illness will affect HR during workout and that's a sign to slow down). But as I said, I'm not an expert and I work with my data.

Now, about Fitbit. Accuracy of the HR monitor for me was always questionable and I never got it working to the level I could make any use of the data (at least during workouts, I think tracking daily activity HR is more or less fine). I used external HR monitoring for several reasons. One is that ANT+ devices like chest straps can connect to your gym machines and you can see HR on the machine. Those devices come with apps showing you lot more in the real-time (for example app from Polar draws HR graph while you're exercising, so you can see those patterns I have mentioned as you go), they are lot more accurate (don't suffer from Fitbit high-intensity training problems for which accuracy dramatically drops down). Since I don't own Fitbit anymore, I use the watch that can connect with external sensors. Very useful, as I take the watch off during workouts and can still monitor my HR. The watch HR (any watch, not just Fitbit) is very sensitive to motion and may even pick up your running cadence as HR. If you do something more complicated, involving bending your wrist, etc. then the noise is very hard to filter in order to obtain accurate HR. That's why for HR-based workouts most of the watches are useless if you want to see those little patterns, be able to see if you taking it too far or your rest is just enough. Also, for walking, I found my old Ionic going 20-30bpm too high just for walking compared to the ECG chest strap.

Your body will let you know if you are taking it too far. You will run out of juice and this will force you to stop. We have plenty of failsafe mechanisms in our bodies that are made to prevent us from harming ourselves. If you have no heart condition you'll be fine. You pretty much described here how my own body works (rising HR quickly to the max levels, dropping, very low RHR, staying in peak for a longer time with not much of an issue - that's also me). In the early days, I got myself tested against heart conditions and none have been found.

Basically, for workouts use reliable equipment, for daily tracking use Fitbit. I have been doing that until my Ionic died and it worked quite well.

If you are worried, see a doctor. Mind that I and most of the other people here will speak from personal experience which may vary from person to person.

[Dominique]

Let’s do some math first. Let’s assume you’re currently 61 kg at 13% body fat. This means you would have been 69 kg / 20.2% BF four months ago. This also means you would have almost halved your total fat mass (from 13.9 to 7.9 kg), which would be very impressive indeed. In terms of looks (using this link as a source), this means going from this:

to somewhere between these:

I personally think it would be very hard to lose 0.5 kg per week for 16 weeks straight while keeping a ratio of 75% fat - 25% lean.

As to linking fat burning abilities to HR stats, I believe you’re way overthinking it. Fat burning occurs when you’re in a caloric deficit overall, plain and simple.

A remark regarding cardio fitness score: the fact yours is expressed as a range indicates it’s been estimated by Fitbit’s algorithm without using maximum effort data. For a more accurate score, run outdoors for 10+ minutes on a flat surface with GPS turned on. You will get a score expressed as a single number. Based on my own experience, the single number score is substantially lower than the range score (and a more realistic representation of VO2max). Ideally, you would run for 12 minutes on a 400 meter track (Cooper’s test, gold standard for VO2max) and measure the distance.

In a nutshell: there’s probably no reason for you to be worried and see a doctor. Just enjoy being fitter and leaner than four months ago!

[emili]

no expert here either. and if you are really worried than you should see a doctor. however, I am a 49 yo female. I am slim and I have a high level of activity. my RHR is anywhere between 48-50 (weekends elevate it due to drinking.. cheers). When I run, my HR goes up quickly and stays in peak or cardio for the entire duration of the effort. When I stop, I am back to normal breathing and an HR somewhere in the low 100 within 30 seconds or so. And in a minute I am back to the 60s. I too sweat af. I think just the general rule of thumb is if your HR goes down quickly once intense activity is over, that is an indicator of heart efficiency and what athletes look for when they train. 

[Jacks_dad]

Hi there, new user. 👍🏻

Just a quick question about more accurate cardio readings. I was quiet pleased with a 50-54 reading but obviously thats just a generalisation so i went for a run today (i hate running so have shied away from it), as far as i'm aware i've done whats required to get the more accurate reading, gps on, run on flat for 13 mins etc, but it still gives the 50-54 reading. Is it a case of one run isn't enough for fitbit to work out cardio levels and i need to put a bit more effort in, or does it still need to work out a days RHR to get its reading ? 

Any info would be much appreciated.

[Colinm39]

@emili  A good response.. I still use HR Recovery and this link gives you one example of measuring it.. comparing your heart in age terms...Even at my age, 80 in a week, I still use it, but my genetics have me recovering quickly.

But, always, get checked when in doubt..

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@emili wrote:

no expert here either. and if you are really worried than you should see a doctor. however, I am a 49 yo female. I am slim and I have a high level of activity. my RHR is anywhere between 48-50 (weekends elevate it due to drinking.. cheers). When I run, my HR goes up quickly and stays in peak or cardio for the entire duration of the effort. When I stop, I am back to normal breathing and an HR somewhere in the low 100 within 30 seconds or so. And in a minute I am back to the 60s. I too sweat af. I think just the general rule of thumb is if your HR goes down quickly once intense activity is over, that is an indicator of heart efficiency and what athletes look for when they train. 

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[Dominique]

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@Jacks_dad wrote:

i've done whats required to get the more accurate reading, gps on, run on flat for 13 mins etc, but it still gives the 50-54 reading..

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Did your run register as such, that is, does it show up in the activity list complete with a map? Which Fitbit do you have? My guess is models with built-in GPS (Ionic) are more reliable than those that rely on a connection to your phone for GPS (e.g. Versa or Charge 3). It may take a couple of trials before your score is updated

[Jacks_dad]

Hi there, thanks for the reply, yep, it's on my app list of exercises, with a map. I have an inspire, will give it a few attempts 👍🏼👍🏼