HR and running - few Fat Burn or Cardio minutes

[Specky]

Hey everyone! Thanks for reading. My main exercise for the last few months has been running. I've gradually improved from 1km to 5km which I'm pretty happy about. But I've noticed that my heart rate goes straight from low (less than the fat burn threshold of 98 bpm) before I start the run, right up to peak (over 151 bpm) within three minutes. It then levels off somewhat, but I generally hit a peak of about 180 bpm around 20-25 min, which is the end of my run. I do feel quite out of breath by the end of it, but within 3-5 minutes everything is back to chill. So the question is, how normal is this, and what does it mean? My FitBit is counting Fat Burn and Cardio minutes, but I hardly ever earn more than 2-3 min. The example below is 0 min Fat Burn, 3 min cardio and 18 min Peak. I'm 51 years old.

[t.parker · Accepted solution]

May be normal, may not. It depends on your health and genetics. Do you feel any symptoms like being out of breath, dizziness, or anything unwanted if you keep your HR this high for a longer period? If not then probably this isn't your peak. Mind that Fitbit zones are very simplified and use a model that may not apply to every individual. In fact, you may not be in your peak but in threshold (one of the definitions states it's the heart rate that you can sustain for about an hour). Looking at your max HR detected (assuming it's not an error in readings) clearly, your zones are not correct. Fitbit uses 220-AGE formula to find your max HR and 220-51 is 169. Now, using HRR (takes into account max HR and RHR) it defines zones. If it uses the wrong max HR your zones are wrong. You may change maximum HR in the Fitbit app to the custom one. For me, the formula doesn't work either as my max HR is 189 but the formula expects 180 but also my threshold HR is very high and Fitbit doesn't take it into account.

About running with such high HR I suggest asking your doctor whether it's normal for you. I will give you two examples of my own runs (21km and 5km):
21km, Time: 1:51:58, Average: 172bpm, Max: 183bpm5km, Time: 22:44, Average: 179bpm, Max: 188bpm

As you can see, my heart jumped to zone 3 (154-163) within 22 seconds in the 5km run (mind, both runs are races so I gave all I had :D) and didn't stay there for too long 🙂 so it is possible that your heart is not working as standard formulas expect. However, I did consult a specialist and had clinical tests done. You may do the same thing if you are worried (but also make sure your Fitbit readings are correct). So to cut the story short:

• If you are worried consult a specialist
• Such things are not rare and may be absolutely normal
• Check whether your Fitbit is tracking your HR accurately (for accuracy, I run only with a chest strap)
• Set your max HR in the app
• Don't panic 🙂

[Specky]

Hi T! Thanks for jumping in! 😀

I'm not worried but perhaps I'm looking for reasons to be worried. Heh, modern tech. You've reassured me.

I have enough data from Fitbit to convince myself that my max HR is much higher than (220-51), so I'll adjust the settings. I've breached 190 several times. But also I think I might pick up a chest strap since there are occasionally artefacts in Fitbit's heart rate data that look suspect: very steep rises and falls in the rate that are far steeper than, say, when I stop to tie a shoelace.

"Do you feel any symptoms like being out of breath, dizziness, or anything unwanted if you keep your HR this high for a longer period?"

I'm not going to pretend that running 4km in 21 min is a doddle. It isn't. The peak recorded heart rate in the last month is 193 for a couple of minutes in my first run after Christmas. It's hard work and at the end of it, sure, I'm huffing and puffing. But it's nothing more than I'd expect. I feel a bit hot, but no dizziness, or anything else unpleasant. And after a 5-10 minute rest, everything is back to being relaxed. I'm pretty sure I couldn't sustain that rate for an hour. I'm aiming for a range of 4-5km in 20-25 minutes, giving it my all as per your examples. If I knew I had to sustain running for an hour, I think the slower pace would give a heart rate in the region 145-155 bpm. That's without actually trying tho!

Anyway, thanks for taking an interest 😉

[t.parker]

I highly recommend to use chest strap when running. Wrist monitors very often mistake cadence for heart rate which may result with unusually high readings later. On the graph you posted it doesn't seem to be the case but it happened to me many times. It usually looks like this (and this is rather severe example):

In this case HR stayed up for over 1km due to cadence noise and then somehow watch locked on. If you want accuracy then chest strap is way to go (or rather run 😋).

[Specky]

Right! I do have some charts like that, where the heart rate (and power) suddenly jump for no obvious reason. But I usually run with a metronome at 155 spm, and the heart rate doesn't seem to track that. I'll watch it carefully though. Wish I could get my cadence up to 180 like yours I'd feel like a Wile E Coyote cartoon! 😆  

[t.parker]

@Specky I also run with metronome set usually to 180-186. If I do HIIT I change the tempo between intervals. I started the same as you, with 155-160 but it didn't take long to 're-program' brain to start doing cadence 180+. You may try to set the metronome to a higher tempo and just skip in place until you get the right rhythm, which helped me to adapt to the new cadence.

About HR, if you use Strava, there is a brilliant feature called Flyby. Some athletes you pass by during your runs allow everyone to see their stats (and these are usually very dedicated athletes so they want to have visibility in the community) so you can take a peek at their HR (mind, I don't say to stalk people, that's bad!). What you're going to see is a variety of different individual readings. Some athletes will run fast with HR quite low (I know a guy who ran 10mi with pace 4:03 and HR barely elevating to 160bpm), then you will find athletes for whom HR shoots up to crazy high values (170-180) and they can sustain it for quite a long time and keep a great pace, too and not finish totally exhausted. The conclusion could be that there is no such thing as "normal". It is all more individual than one might think. This is a reason why cardiologists hate fitness trackers. Trackers are in general a good thing but they brought so much confusion to people who started to get worried about absolutely nothing just because they didn't fit the "normal".