Calorie burn from exercise low - "low" HR??

EmBlazes

Hi. Was wanting some advice about using HR to measure calorie burn. I've just got the Garmin Vivofit because I wanted a better idea of how active I am just in daily activity (thus the step counter) but it also has a HRM which I use when I'm doing spin classes, playing squash etc. I know HR isn't a totally accurate way to measure calorie burn but it is better than nothing!

So I have been a bit shocked by how few calories it is allocating for my activities. The first time I did a spin class with the HRM on I only earned 226 calories. I would normally allocate 400-500 calories for this. In terms of exertion, I had sweated buckets (the top half of my tshirt was wet with sweat) and for several tracks I was breathing pretty hard. I was cycling for 50 minutes and did 28km in that time (according to the bike).

Today I played squash for 40 minutes. It was pretty much non-stop although I wasn't sweating all that much and I don't run around too much (just because I'm not THAT good). I got 151 exercise calories from the HRM. It was working the whole time but my HR never got above "zone 2", even for a really energetic rally.

Is it possible that I'm really fit so my heart rate is quite low??! I've been exercising consistently for years now. I also have hypothyroidism (controlled with Thyroxine) which can also cause you to have a slower heart rate for your age so I wondered if that might be the reason for the low readings.

My aim is still to lose weight and I'm concerned that I shouldn't be eating exercise calories if I'm earning so few. I see a lot of other people posting calorie burns in the thousands. Am I missing something?

Would really appreciate your advice.

glevinso

Some people have naturally lower heart rates. Since HR only kinda sorta correlates to calorie burn, you might just be one of those people for whom it simply doesn't work.

Do the spin bikes you use have anything that tells you watts or kilojoules? If you can get onto a bike that does, that will give you much better data than a HRM.

EmBlazes

Thanks for your reply. Unfortunately we have Watt bikes in the gym but not in the group cycle class. The ones in the group cycle class only show calories burned if you sync a HRM (which no one seems to be able to get to work). But again - we'd be back to my low HR not giving me a great burn rate
There is no indication of watts so it is sometimes hard to know how much resistance you are using. I just try to go by what the instructor says and I always manage to do more than the instructor indicates ("more than 20km is your goal") so I think I'm working hard enough from that perspective.

alekth

If you're never getting out of zone 2 and your hrm is working correctly, and you're exerting yourself, then likely the zones are wrong.

Are the resting and max heart rate set correctly in the garmin settings? If you're using the default ones, maybe they are too far off from your own. For the resting heart rate, try to measure it right after waking up, perhaps keep the strap close to the bed and put it on, relax again and check heart rate. The max heart rate is trickier, and if you're measuring it on your own, it's best to just do some interval sprinting or equivalent, pushing yourself as far as you can while you still feel fine, max will be close to the value at that time. If you have a trainer who can watch over you, it's better to do it on a treadmill. Start at a slow speed, run for a while, then go up a bit, rinse and repeat, going faster/steeper until your hr is not going any higher. I suppose this can be done with a stationary bike controlling for resistance and speed as well. Just don't go 101% on your own, just in case.

cwolfman13

If you have a higher than average resting HR or lower than average resting HR, your calorie burns with a HRM are going to be skewed. They're only relatively accurate for calorie burn anyways...but they're going to be less so if your HR is outside of average.

sijomial

Can you custom set your min/max HR on your device? Setting for VO2 max?
Makes quite a difference (I have an unusually low min HR and a slightly higher than average max HR for my age).

My suggestion would be to use the Wattbike to estimate a ride of similar exertion to your Spinning class. The Wattbikes are supposedly very accurate in measuring power and when I compare a Wattbike Pro to my HRM that has custom settings including tested VO2 max they come out very close which gives me a fair amount of confidence in both devices.

The numbers you are getting are ridiculously low if you have a reasonable level of fitness.

Azdak

Nothing I've read about activity trackers convinces me they are accurate when used during exercise.

The problem with watt readings on most stationary bikes is that they don't accurately account for wind resistance so the watts are an overestimate as well. To be accurate, you need a power meter.

alekth

Yeah, generally I don't trust my vivofit too much with the activity calories, although lately it seems Garmin have fixed a fair amount of bugs with it (part of them appearing to be on the online platform rather than the device itself, since I have gotten ridiculously high measurements during an activity and had them drop to nearly half of that once synced with the garmin connect). The vivofit doesn't use the Firstbeat algorithm that's on the more expensive Garmin devices either, just a generic formula that takes HR, activity class, weight and gender. So take the time to set all of those at close to correct values (set them on the global garmin connect profile since now that I look at it, user settings on the device itself doesn't have activity class, and the HR fields would need manual calculation.)
On the other hand at least the HR measurements are actually good by themselves since it's a proper chest strap.

For me it seems to err on the high side, but especially as of late it seems to be coming pretty close.

EmBlazes

Thanks for the advice everyone! Yes I can set the heart rate zones manually on the Garmin Connect site and they are currently at "default" which probably explains why I'm not getting what I think is an appropriate burn. The idea about checking my resting heart rate is a really easy thing I can do so I will try that tomorrow and see what it comes back with.

Did a 3 hour walk in the countryside today and earned 642 calories according to the vivofit. Most of the time I was in zones 0 and 1. Now it isn't strenuous walking and occasionally I was in zone 2 when climbing a steeper incline. I'm still thinking I should re-jig the zones but I'm going to read up about it first so I know what I'm doing.

Would have loved to have gone for one of the more expensive GPS-HR monitor type devices but just really wanted something base level at the moment that at least gives me an IDEA of what I'm burning and helps me get off my butt when I've been sitting too long

Again - thanks - really helpful advice.