Calories calculated by the Garmin?

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zill
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Calories calculated by the Garmin?

Postby zill » Sat Jan 31, 2015 9:47 am

How accurate is it assuming one has a power meter as well as a heart rate monitor?

defy1
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Re: Calories calculated by the Garmin?

Postby defy1 » Sat Jan 31, 2015 4:43 pm

have ever tried googling some of your questions?

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Carrots
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Re: Calories calculated by the Garmin?

Postby Carrots » Sat Jan 31, 2015 6:58 pm

Google? What's google? :D

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bychosis
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Re: Calories calculated by the Garmin?

Postby bychosis » Sat Jan 31, 2015 7:05 pm

Carrots wrote:Google? What's google? :D
B. I. C. Y. C. L. E. S. .net....
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Re: Calories calculated by the Garmin?

Postby chriscole » Sat Jan 31, 2015 7:36 pm

zill wrote:How accurate is it assuming one has a power meter as well as a heart rate monitor?
Trick question. Answer is: "It doesn't matter". ;-)

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Re: Calories calculated by the Garmin?

Postby zill » Sat Jan 31, 2015 8:19 pm

chriscole wrote:
zill wrote:How accurate is it assuming one has a power meter as well as a heart rate monitor?
Trick question. Answer is: "It doesn't matter". ;-)
What if you are strictly calorie counting?

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Re: Calories calculated by the Garmin?

Postby bychosis » Sat Jan 31, 2015 11:45 pm

After a while you will work out how accurate it is for you because everyone is different, but if you are trying to work it out down to the nearest 10% I reckon it's not going to be accurate enough. Its still not going to make up for all the estimation around the time you are not using your garmin eg eating, sleeping, walking to the bathroom, doing yours business, entering in depth questions to a cycling forum using a keyboard etc.
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zill
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Re: Calories calculated by the Garmin?

Postby zill » Sun Feb 01, 2015 1:28 am

bychosis wrote:After a while you will work out how accurate it is for you because everyone is different, but if you are trying to work it out down to the nearest 10% I reckon it's not going to be accurate enough. Its still not going to make up for all the estimation around the time you are not using your garmin eg eating, sleeping, walking to the bathroom, doing yours business, entering in depth questions to a cycling forum using a keyboard etc.

Got all those other things covered. Just need the extra calories I burn while riding accurately.

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kb
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Re: Calories calculated by the Garmin?

Postby kb » Sun Feb 01, 2015 6:46 am

If you lose weight more quickly than you expect, it's overestimating. If you lose weight more slowly, it's under estimating ;-)
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Re: Calories calculated by the Garmin?

Postby bychosis » Sun Feb 01, 2015 7:06 am

zill wrote:
bychosis wrote:After a while you will work out how accurate it is for you because everyone is different, but if you are trying to work it out down to the nearest 10% I reckon it's not going to be accurate enough. Its still not going to make up for all the estimation around the time you are not using your garmin eg eating, sleeping, walking to the bathroom, doing yours business, entering in depth questions to a cycling forum using a keyboard etc.

Got all those other things covered. Just need the extra calories I burn while riding accurately.
How do you measure all those other things ACCURATELY? My point was that pretty much all calorie expenditure will be estimated to just as accurately as the Garmin, which is exactly that, an estimate. Do you use a HRM 24/7?
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Re: Calories calculated by the Garmin?

Postby CKinnard » Sun Feb 01, 2015 7:35 am

test it yourself. ride over the same 1 or 5km route 4 times at the same pace, preferably flat, and make sure you use the same cadence without ever freewheeling.
first with no HRM or PM
second with HRM only
third with PM only
forth with HRM and PM

I presume the garmin defaults to calculating energy expenditure via the PM only, when you have it on, which would be the most accurate.

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Re: Calories calculated by the Garmin?

Postby zill » Sun Feb 01, 2015 11:18 am

bychosis wrote:
zill wrote:
bychosis wrote:After a while you will work out how accurate it is for you because everyone is different, but if you are trying to work it out down to the nearest 10% I reckon it's not going to be accurate enough. Its still not going to make up for all the estimation around the time you are not using your garmin eg eating, sleeping, walking to the bathroom, doing yours business, entering in depth questions to a cycling forum using a keyboard etc.

Got all those other things covered. Just need the extra calories I burn while riding accurately.
How do you measure all those other things ACCURATELY? My point was that pretty much all calorie expenditure will be estimated to just as accurately as the Garmin, which is exactly that, an estimate. Do you use a HRM 24/7?
The basal metabolic rate and metabolic rate for daily activities are all pretty standard and I am no genetic freak. Even if one over or under estimates, it won't be very far off. However, with exercising there is bigger disprecensy. For example, drafting in a group at 40km/hr and soloing at 40km/hr on a flat course have very different metabolic effects.

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Re: Calories calculated by the Garmin?

Postby zill » Sun Feb 01, 2015 11:19 am

CKinnard wrote:test it yourself. ride over the same 1 or 5km route 4 times at the same pace, preferably flat, and make sure you use the same cadence without ever freewheeling.
first with no HRM or PM
second with HRM only
third with PM only
forth with HRM and PM

I presume the garmin defaults to calculating energy expenditure via the PM only, when you have it on, which would be the most accurate.
A lot of people have said that heart rate was the most important factor in determining calories burned but I personally also feel that power should have the highest effect.

What is the science behind why the PM is the most important factor and heart rate is almost negligible in calorie determination?

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Re: Calories calculated by the Garmin?

Postby bychosis » Sun Feb 01, 2015 11:43 am

zill wrote:The basal metabolic rate and metabolic rate for daily activities are all pretty standard and I am no genetic freak. Even if one over or under estimates, it won't be very far off. However, with exercising there is bigger disprecensy. For example, drafting in a group at 40km/hr and soloing at 40km/hr on a flat course have very different metabolic effects.
If you are using estimates like that, then a garmin with HRM and power is more than accurate enough. Pure GPS logging isn't very accurate as it doesn't take into account effort related to headwinds etc. eg I can ride with a strong headwind at 20km/h working hard and then when I turn around and get up to 40 with with a tailwind and less effort and it will assume I'm working harder at 40km/h. Add a HRM and you get a better idea because it incorporates effort somewhat, add power and it should in theory be bette again but it's still an estimate.
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zill
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Re: Calories calculated by the Garmin?

Postby zill » Sun Feb 01, 2015 12:15 pm

bychosis wrote:
zill wrote:The basal metabolic rate and metabolic rate for daily activities are all pretty standard and I am no genetic freak. Even if one over or under estimates, it won't be very far off. However, with exercising there is bigger disprecensy. For example, drafting in a group at 40km/hr and soloing at 40km/hr on a flat course have very different metabolic effects.
If you are using estimates like that, then a garmin with HRM and power is more than accurate enough. Pure GPS logging isn't very accurate as it doesn't take into account effort related to headwinds etc. eg I can ride with a strong headwind at 20km/h working hard and then when I turn around and get up to 40 with with a tailwind and less effort and it will assume I'm working harder at 40km/h. Add a HRM and you get a better idea because it incorporates effort somewhat, add power and it should in theory be bette again but it's still an estimate.
That' makes sense. With HRM and PM, if you only had one which would you use to estimate calories on the Garmin?

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Re: Calories calculated by the Garmin?

Postby zill » Sun Feb 01, 2015 2:40 pm

In thinking about which HR or PM has more influence, one could get fitter and more efficient at pedaling and so not "putting in as much" when pedaling at a particular power output. For example would a fit person pedaling at 160W burn less calories than an unfit person pedaling at 160W. You'd definitely expect the fitter person to have a lower heart rate at 160W than the unfit person.

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Re: Calories calculated by the Garmin?

Postby brendan c » Sun Feb 01, 2015 5:15 pm

If you had a PM which directly measures input (see total work on Strava (Kj)) why would it then use a guess based on HR/speed/whatever? You just need to understand how to convert that work into Calories burnt assuming your PM is 98-99% accurate (good enough for your purposes)

Garmin/Strava/GC etc... would then have to guess how efficient you are. The efficiency of a human on a bike is somewhere between 0.23 and 0.27 so a possible 15% error. Or say it uses 25% as a measure then it's +/- 7.5%. I just had a look at Strava and it's showing work, but not Calories burnt.

A quick and dirty calculation is just to take work in Kj and convert directly to Calories (really Kilocalories) because the conversion is 1/4.184 = 0.239 which is close enough to the 23 to 27% above. If you wanted to be a bit closer convert directly then multiply by 1.07 (see the link below)
So if my ride yesterday was 1300kJ of work. I've burned roughly 1391Cal or 5440Kj

A powermeter isn't making an estimation, the only variables to consider are PM accuracy and your own effiency.

First hit on google: http://www.ncbi.nlm.nih.gov/pubmed/18803095" onclick="window.open(this.href);return false; this study says 0.257 +/- 0.0245.

Or... you could just search for this, or ask a Year 9 or 10 science teacher

Edit: Grammar
Last edited by brendan c on Sun Feb 01, 2015 11:15 pm, edited 1 time in total.

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Re: Calories calculated by the Garmin?

Postby CKinnard » Sun Feb 01, 2015 6:06 pm

zill wrote:A lot of people have said that heart rate was the most important factor in determining calories burned but I personally also feel that power should have the highest effect.

What is the science behind why the PM is the most important factor and heart rate is almost negligible in calorie determination?
Which people say HR is more important? Maybe this is in relation to running = no power meter.

HR is not as good a predictor of energy expended. That's well established in the literature, although Polar (heart rate monitor company) felt the regression equations were practically useful.

You cannot get better than actual power generated, though efficiency is not accounted for. Nevertheless, I think a more accurate estimate of efficiency is possible than an estimate of the inputs that vary HR.

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Re: Calories calculated by the Garmin?

Postby toolonglegs » Sun Feb 01, 2015 7:54 pm

Your pm is telling you your actual work... it is not estimating anything. The only thing you need to estimate is your efficiency. But as that is somewhere around 21-25% it is only a % here or there.
Forget your heart rate totally ... ignore it!.

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Re: Calories calculated by the Garmin?

Postby zill » Sun Feb 01, 2015 9:48 pm

CKinnard wrote:
zill wrote:A lot of people have said that heart rate was the most important factor in determining calories burned but I personally also feel that power should have the highest effect.

What is the science behind why the PM is the most important factor and heart rate is almost negligible in calorie determination?
Which people say HR is more important? Maybe this is in relation to running = no power meter.

HR is not as good a predictor of energy expended. That's well established in the literature, although Polar (heart rate monitor company) felt the regression equations were practically useful.

You cannot get better than actual power generated, though efficiency is not accounted for. Nevertheless, I think a more accurate estimate of efficiency is possible than an estimate of the inputs that vary HR.
The guys at the bike shop told me the only way to get calories burned is through heart rate. They said power isn't useful at all. They sell Polar and running watches as well. Maybe they got this impression through them.

Oddly enough my gym has a treadmill which outputs power depending on the pace it is running at.
Last edited by zill on Sun Feb 01, 2015 9:52 pm, edited 1 time in total.

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Re: Calories calculated by the Garmin?

Postby zill » Sun Feb 01, 2015 9:51 pm

brendan c wrote:If had a PM directly measure input (see total work on Strava (Kj)) why would it then use a guess based on HR/speed/whatever? You just need to understand how to convert that work into Calories burnt assuming your PM is 98-99% accurate (good enough for your purposes)

Garmin/Strava/GC etc... would then have to guess how efficient you are. The efficiency of a human on a bike is somewhere between 0.23 and 0.27 so a possible 15% error. Or say it uses 25% as a measure then it's +/- 7.5%. I just had a look at Strava and it's showing work, but not Calories burnt.

A quick and dirty calculation is just to take work in Kj and convert directly to Calories (really Kilocalories) because the conversion is 1/4.184 = 0.239 which is close enough to the 23 to 27% above. If you wanted to be a bit closer convert directly then multiply by 1.07 (see the link below)
So if my ride yesterday was 1300kJ of work. I've burned roughly 1391Cal or 5440Kj

A powermeter isn't making an estimation, the only variables to consider are PM accuracy and your own effiency.

First hit on google: http://www.ncbi.nlm.nih.gov/pubmed/18803095" onclick="window.open(this.href);return false; this study says 0.257 +/- 0.0245.

Or... you could just search for this, or ask a Year 9 or 10 science teacher
For some reason, for the same ride which include power data, Strava always overstates calories burned compared to the garmin unit. I wonder if Strava takes into account one's metabolic rate as well? Or does Strava assume a more inefficient power to calorie conversion?

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Re: Calories calculated by the Garmin?

Postby toolonglegs » Sun Feb 01, 2015 10:32 pm

You have a device that tells you exactly how much work you have done... You know within 2% how mechanically efficient a human body is ... Yet you still want to worry about a guesstimate from your heart rate?

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Re: Calories calculated by the Garmin?

Postby CKinnard » Sun Feb 01, 2015 11:20 pm

zill wrote:The guys at the bike shop told me the only way to get calories burned is through heart rate. They said power isn't useful at all. They sell Polar and running watches as well. Maybe they got this impression through them.

Oddly enough my gym has a treadmill which outputs power depending on the pace it is running at.
Unfortunately, my experience with LBSs is that I feel compelled to research the buggery out of a topic before I seek their advice. That way I have more insight into where they are coming from.

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Re: Calories calculated by the Garmin?

Postby zill » Mon Feb 02, 2015 10:12 am

toolonglegs wrote:You have a device that tells you exactly how much work you have done... You know within 2% how mechanically efficient a human body is ... Yet you still want to worry about a guesstimate from your heart rate?
I see that. Never liked to wear a heart rate monitor anyway. I wonder if the efficiency is dependent on the heart rate at all?

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Re: Calories calculated by the Garmin?

Postby GAV!N » Tue Feb 03, 2015 11:54 am

zill wrote:
bychosis wrote:After a while you will work out how accurate it is for you because everyone is different, but if you are trying to work it out down to the nearest 10% I reckon it's not going to be accurate enough. Its still not going to make up for all the estimation around the time you are not using your garmin eg eating, sleeping, walking to the bathroom, doing yours business, entering in depth questions to a cycling forum using a keyboard etc.

Got all those other things covered. Just need the extra calories I burn while riding accurately.
So how many calories does it take to post a stupid question then?

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