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#1
Old 04-09-2011, 04:28 PM
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How accurate is the calorie count on my Garmin?

Sorry if this doesn't belong here - I hope there is some sort of factual answer for this.

I wear a Garmin on my runs and bike rides, and use the HR monitor. It tracks my pace, distance, elevation, cadence, etc. How accurate will the calorie count be? I'm just surprised that I'm burning upwards of 650 calories for an hour of moderately hard running (female, 30, 165 lbs., moderately fit), and sometimes up to 1100 calories for an hour and a half hard ride.
#2
Old 04-09-2011, 06:31 PM
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It depends. The later Garmin X models (i.e. 405CX) uses heart rate as well as user profile and GPS info to make the calorie calculation (based on a license from Polar Technologies). However, it really is just an approximation based on a model, and it seems that many feel that the calculation is somewhat low.

You can try to calibrate it by wearing it on a treadmill and comparing calories used ( the treadmill knows the time, distance, gradient and your weight, so working out the calories is trivial). This will only work on a heartrate based system, and won't help with the older Garmins. Also, if you upload a workout to a site like mapmyrun, their calorie calculation uses map data to work out vertical movement as well as distance, and can be a bit more accurate in their calculation.

At the end of the day, though, the calories burned is just a number that may reflect reality, in the same way that the nutritional value label on a food item may or may not be accurate. Use the number as a guide, but don't let it rule your life or eating. You can measure yourself against yourself to see improvements, but that is generally about it.

I can't comment on your numbers because you don't mention distance - I hit about 800-900 calories for a 50 minute 10km run, and about 1000-1100 for a 1 hour bike ride (16-17 miles), but I have much more weight to shift (in every sense) and am a male (which bumps up the numbers).

Si
#3
Old 04-09-2011, 07:18 PM
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Quote:
Originally Posted by EmAnJ View Post
Sorry if this doesn't belong here - I hope there is some sort of factual answer for this.

I wear a Garmin on my runs and bike rides, and use the HR monitor. It tracks my pace, distance, elevation, cadence, etc. How accurate will the calorie count be? I'm just surprised that I'm burning upwards of 650 calories for an hour of moderately hard running (female, 30, 165 lbs., moderately fit), and sometimes up to 1100 calories for an hour and a half hard ride.
650 for a moderately hard hour of running looks more than reasonable. I would actually expect a good bit more, but I'm male and my definition of "moderately hard" may be higher than yours. If you ballpark 100 calories per mile, that will give you a very conservative estimate of what your calorie burn should be for calorie-counting purposes.

ETA: I should also add and ask, I've always wondered how closely connected heart rate and energy expenditure is. The reason I ask is during the winter, I do a lot of ice skating, and I've worn my heart rate monitor at times just to get an idea of what it thinks I'm burning. I've done skates of an hour and a half or so that register 1200 calories, but it doesn't feel anywhere near as hard as a running workout that gets me to 1200 calories (about a 10 mile run or so, at 8:00/mile). There's simply no way I believe an hour and a half skate is burning the same amount of calories as a 10 mile run. It certainly doesn't feel like it when I'm done.

Last edited by pulykamell; 04-09-2011 at 07:22 PM.
#4
Old 04-09-2011, 07:19 PM
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The heart rate monitors are very good guides. Your heart rate really is a very good indicator of energy being expelled. The conversions are not complicated, and reading a heart rate is pretty straightforward.


.

Last edited by Philster; 04-09-2011 at 07:20 PM.
#5
Old 04-09-2011, 08:43 PM
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Thanks guys.

I have a Garmin Forerunner 405 and upload my data to Garmin Connect. My one hour run is about six miles in hilly terrain (like today) and about 6.5 in flat terrain.

Garmin Connect, if none of you know what it is, shows you a ton of data, including elevation gain and loss, distance, pace, HR, etc., all on one page. It's a pretty cool tool.

I looked at my data from my run today and for 6.07 miles in 1 hour, 3 minutes in very hilly terrain, it says I burned 729 calories. I suppose that's pretty accurate considering what it's basing the calculation on.
#6
Old 04-09-2011, 08:45 PM
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Originally Posted by pulykamell View Post

ETA: I should also add and ask, I've always wondered how closely connected heart rate and energy expenditure is. The reason I ask is during the winter, I do a lot of ice skating, and I've worn my heart rate monitor at times just to get an idea of what it thinks I'm burning. I've done skates of an hour and a half or so that register 1200 calories, but it doesn't feel anywhere near as hard as a running workout that gets me to 1200 calories (about a 10 mile run or so, at 8:00/mile). There's simply no way I believe an hour and a half skate is burning the same amount of calories as a 10 mile run. It certainly doesn't feel like it when I'm done.
I wonder that too. My husband has a Garmin as well and has been wearing it for his back country ski trips this spring. Some days his moving time is around 3 hours and he burns around 3000 calories in that time. It just seems like a lot, but I guess if it's basing it on his HR it must be fairly close.
#7
Old 04-10-2011, 12:31 AM
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Originally Posted by EmAnJ View Post
Thanks guys.

I have a Garmin Forerunner 405 and upload my data to Garmin Connect. My one hour run is about six miles in hilly terrain (like today) and about 6.5 in flat terrain.

Garmin Connect, if none of you know what it is, shows you a ton of data, including elevation gain and loss, distance, pace, HR, etc., all on one page. It's a pretty cool tool.

I looked at my data from my run today and for 6.07 miles in 1 hour, 3 minutes in very hilly terrain, it says I burned 729 calories. I suppose that's pretty accurate considering what it's basing the calculation on.
Yep, those numbers look like what you'd expect for your data (including weight). The more advanced formula I read for what you should expect to burn per mile is .75 * your weight in pounds. So, for a 165 pound person, 6.07 miles would equal an expenditure of 751 calories. Pretty close to what your HRM is giving you. I use the 100 calories a mile if I need to estimate for calorie counting purposes (remember, that you would have burnt calories anyway if you didn't do anything, so the 751 calories includes your base metabolic rate calories, too.)

I can just about believe the numbers for skiing--that gets pretty intense. It's the skating that I wonder about. The charts I see say something like around 4-500 calories per hour. That sounds about right to me. My HRM is telling me I'm burning about 800 calories per hour. It just seems too good to be true for the perceived level of exertion. According to the charts, that's getting towards the "competitive speed skating" effort end of the chart. I mean, I'm just having a leisurely time out there that feels like almost no effort at all.

Last edited by pulykamell; 04-10-2011 at 12:34 AM.
#8
Old 04-10-2011, 08:27 AM
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Originally Posted by Philster View Post
The heart rate monitors are very good guides. Your heart rate really is a very good indicator of energy being expelled. The conversions are not complicated, and reading a heart rate is pretty straightforward.
This is only the case if you know your VO2max, or can estimate it from the heart-rate response to starting exercise (a slower heart rate increase indicates a higher VO2max ). Calories is energy, but the easiest way to work it out is from the weight moved through a distance. Oxygen consumption is directly related to energy output, but is hard to measure in the real world. You can use the heart-rate as a proxy, but only if you know how much each beat pumps and how much oxygen goes round with each pump - basically, your VO2max. But you need to know that from a measured exercise. I think that the Polar technology that Garmin licensed in the 405CX combines Distance, Time, Weight and Heartrate to give a really good calculation, but this only applies to that specific model of Garmin (and the 310XT). And it must have been expensive, the 405CX was (on release) considerably more expensive than the 405 (~60).
Quote:
Originally Posted by EmAnJ
I wonder that too. My husband has a Garmin as well and has been wearing it for his back country ski trips this spring. Some days his moving time is around 3 hours and he burns around 3000 calories in that time. It just seems like a lot, but I guess if it's basing it on his HR it must be fairly close.
As I noted in my original post, many older Garmin models do NOT use Heart-Rate to calculate Calories - from the FAQ for my Garmin 301
Quote:
Originally Posted by Garmin FAQ
The calorie readings in the Forerunner and Edge units are calculated using a combination of speed, weight and time. This means that for indoor sports or those where there is no GPS signal available, or for activities that involve no movement (e.g. use of gym equipment) the unit will not display a calories reading.
Given that a calorie use of 3000 in 3 hours is the equivalent (more or less) of running 30 miles in that time (I also use 100 calories per mile as per pulykamell) I would suggest that the calorie calculation is based on Time, Distance and profile weight. You can cover a long distance on skis without massive energy expenditure.

Si
#9
Old 04-10-2011, 08:27 AM
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I think consistency is more important than absolute accuracy: if your HRM is always 10% high, that doesn't matter at all: over time, you amass a bunch of data about calories in and calories out, and you use that data to make decisions. So if you THINK you average a burn of 1000 calories from exercise a day and think you have to eat 2500 to maintain you weight, it really doesn't matter if in some sort of absolute sense you actually burn 900 and, because your counting is also consistently off, you "really" have to eat 2200.

A bigger question is if the various calorie counting programs can be off because of external factors: if it swings from 5% under to 5% over, that's a bigger deal.
#10
Old 04-10-2011, 10:14 AM
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Thanks si. He actually has the 405CX. He does work hard because he's skinning up the side of a mountain about three quarters of the time and his HR remains in the 160s or 170s for extended amounts of time.

Manda Jo, thanks for your input. I am aware of the theory behind losing weight, and though that is my goal, I am not counting calories right now, rather, I'm using the Weight Watchers points program. Seems to be working so far.

Last edited by EmAnJ; 04-10-2011 at 10:15 AM.
#11
Old 04-10-2011, 11:35 AM
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Originally Posted by EmAnJ View Post
Manda Jo, thanks for your input. I am aware of the theory behind losing weight, and though that is my goal, I am not counting calories right now, rather, I'm using the Weight Watchers points program. Seems to be working so far.
I wasn't trying to tell you how it works: I know you know that. I just mean that it's more important that it be consistent than that it be accurate: a HRM that was always 20% below would be more useful than one that was anywhere from 10% below to 10% above, but someone might describe the later as more accurate, or accurate more often, than the former. I am interested to know if anyone knows if the inaccuracies can be counted on to be consistent.
#12
Old 04-10-2011, 01:08 PM
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In my experience with iron men athletes counting down to the last calorie, and measuring burn rates through even modest HRM, most are able to pin down their weight loss/gain via calorie in vs. calories out measurements.... and the calories out measurement is pretty much just HRM readouts.

We're talking accuracy down to 1-2 pounds overall over several weeks.

I think that is enough to say that a decent HRM is about all you need. You can get 98% of what you need out of one that has the basics about you loaded into it.

It is possible to drill it down to a even finer degree.... but given what even elite athletes seem to accomplish with every stitch of weight in mind... you're probably good to go.
#13
Old 04-10-2011, 01:16 PM
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Quote:
Originally Posted by EmAnJ View Post
I'm just surprised that I'm burning upwards of 650 calories for an hour of moderately hard running (female, 30, 165 lbs., moderately fit).
That sounds about right - in fact, I'd say 650 sounds a bit low for an hour's hard running.
#14
Old 04-10-2011, 02:41 PM
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Originally Posted by EmAnJ View Post
Thanks si. He actually has the 405CX. He does work hard because he's skinning up the side of a mountain about three quarters of the time and his HR remains in the 160s or 170s for extended amounts of time.
If he is at a significant altitude, the calculations will be somewhat high due to lower O2 levels (so the heart beats faster while pumping less than VO2max). However, I am not trying to minimise the effort that he is putting in. I wish I could keep my heart-rate elevated like that for three hours.

Si
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