Calorie Usage

R8JimBob88

Hi folks,

Just a quick question. I have been on a ride today with the Garmin 500 and HR monitor, when I have uploaded the route to Garmin Connect, it shows that I have burned 2,525 calories.

When I have uploaded the same route to Ride with GPS, it reckons I have burned 3,216.

I know neither of them will be very accurate but with there being such a big difference...

Anyone know why this is? Worth paying attention to?

Cheers

Anonymous

It just shows you not to trust the calorie readings on either.

R8JimBob88

Suppose I was expecting somthing like that. Is there a way to find out more accurately how many I've burned?

John.T

General consensus on the Garmin website forum is that the 500 / Connect combo reads around 50% low. The one on ridewithgps is probably closer but I would not take too much notice of any of them.
IMO ridewithgps is a better site to use.

SBezza

R8JimBob88 wrote:

Suppose I was expecting somthing like that. Is there a way to find out more accurately how many I've burned?

Only way is to get a power meter, but a bit of an expensive way to just see what calories you have used. Just take the Garmin 500 figures as a rough guide.

Pokerface

How far and how hard was the ride? Average speed?

R8JimBob88

Ride was 45 miles in 2hr 45ish. I'm fairly new to the bike so for me it was pretty hard. Only 353m of ascent and average HR was 81% of max. Average speed was 16.4Mph

SBezza

R8JimBob88 wrote:

Ride was 45 miles in 2hr 45ish. I'm fairly new to the bike so for me it was pretty hard. Only 353m of ascent and average HR was 81% of max. Average speed was 16.4Mph

I would say the calories are quite a bit out. I know we are all different but I did 2 rides this week, a hard 2 hours (38 miles) which was reported as 1100 Kcal, and a slower 3.5 hours ( 58 miles) which was about 1300 KCal.

The Garmin will use a mathematical equation to get energy usage, and this will incorporate your MaxHR (if you rely on the one calculated by Garmin, it is likely to be wrong), age and weight as some of the data. If any of these points of data are not correct it is likely to be well out, compared with just being out.

R8JimBob88

I've already input my age, weight and HR zones into the device. Max HR is currently 203bpm.

Pokerface

Yeah, I would guess that ride to be less than 2000 cals. Closer to 1500 to be honest.

Not sure what age you are, but I think I read somewhere that reducing your age that you input into the device helps a bit to get a more accurate read.

meanredspider

Does anyone know how efficient the body is at extracting the calories from food? The theoretical 250Kcals in a choc bar converts to what? Some gets used in eating, digesting and metabolising the thing. Some presumably remains in waste products (else you wouldn't be able to light your farts). I assume people are really only interested in the calories in calories out measurement in this discussion?

John.T

http://connect.garmin.com/activity/57706790
This is as close as I have on my list. I am 68 years old, max HR 174 and weigh 168lbs. Kcal is 1383 on Garmin Connect but 3847 on rwgps. I have added the bike weight (26lbs) on rwgps and the elevation gain seems more reliable but higher (+636m / -636m) to Connect's +543m / -548m. The Connect elevation never tallies even after trying the correction. The figures on this ride are closer than on many. I have got home 100m higher than I left once.
Based on sBezza's figures I would say the Connect Kcal figure is closer to correct. I would not take too much notice of them though. They are just a calculation based on an algorythm, not a real measurement.

itboffin

I had exactly the same problem today with my Garmin 705, connect & RWGPS websites.

2300cals or 2900cals for 41 miles in 2hrs 50 min with 733m ascent, I doubt any of the data were accurate, I passed several height markers none of which matched my Garmin.

That said it was my first ride with the unit so I might very well be missing something in the set up.

I still enjoyed all the lovely stats

StefanP

If you feel tired then say job well done!

Pokerface

If you follow the Garmin figures on calorie usage - just don't be surprised if you gain weight!!

Jeff Jones

meanredspider wrote:

Does anyone know how efficient the body is at extracting the calories from food? The theoretical 250Kcals in a choc bar converts to what? Some gets used in eating, digesting and metabolising the thing. Some presumably remains in waste products (else you wouldn't be able to light your farts). I assume people are really only interested in the calories in calories out measurement in this discussion?

From memory I think it's between 19-28% efficient. A useful rule of thumb is to assume ~24% efficiency so you can simply equate kJ of work done (which you can measure with a power meter) to food calories burned.

So to burn off that chocolate bar you need to ride at 200W for ~21minutes (if I've got my working right).

To R8JimBob88, I'd agree with Pokerface and guesstimate between 1500-2000 cals for your ride. And that's making a few assumptions like your average power being 170-180W, your weight being around 75kg and your efficiency being closer to 20% than 25%.

Pokerface

Jeff Jones wrote:

meanredspider wrote:

Does anyone know how efficient the body is at extracting the calories from food? The theoretical 250Kcals in a choc bar converts to what? Some gets used in eating, digesting and metabolising the thing. Some presumably remains in waste products (else you wouldn't be able to light your farts). I assume people are really only interested in the calories in calories out measurement in this discussion?

From memory I think it's between 19-28% efficient. A useful rule of thumb is to assume ~24% efficiency so you can simply equate kJ of work done (which you can measure with a power meter) to food calories burned.

I'm not sure if that's what he was asking. I thought he was asking - if he eats a chocolate bar that the wrapper says has 250cals in it - how much of that is actually absorbed into the body.

I may be wrong though - and maybe your answer still stands.

I thought the efficiency figures you quoted were for something else. (used in the calculation of work done in kJ to calories used?)

Jeff Jones

Pokerface wrote:

I'm not sure if that's what he was asking. I thought he was asking - if he eats a chocolate bar that the wrapper says has 250cals in it - how much of that is actually absorbed into the body.

I may be wrong though - and maybe your answer still stands.

I thought the efficiency figures you quoted were for something else. (used in the calculation of work done in kJ to calories used?)

Good point - I was just thinking in a cycling sense.

I would say if you eat a chocolate bar worth 250cals then nearly all of it is broken down and absorbed. There's a little bit of energy used to digest it but I believe you will end up getting most of that 250cals of chocolatey goodness. What you decide to do with it is another matter.

Luckily our bodies are not capable of digesting things via antimatter annihilation or a mini black hole. That simple chocolate bar could be worth up to 450 terajoules!

meanredspider

Thanks - yes, that was exactly what I was asking (how much ends up in my bloodstream) as it seemed to me that worrying about the accuracy of what we expend to +/-x% is silly if the accuracy of what we take in is less accurate than that.

Pokerface

meanredspider wrote:

Thanks - yes, that was exactly what I was asking (how much ends up in my bloodstream) as it seemed to me that worrying about the accuracy of what we expend to +/-x% is silly if the accuracy of what we take in is less accurate than that.

If you eat that chocolate bar REALLY fast, you don't absorb all the calories. It goes down too fast

meanredspider

Pokerface wrote:

If you eat that chocolate bar REALLY fast, you don't absorb all the calories. It goes down too fast

Chocolate? Never touch the stuff... :oops:

Garz

I generally take off 20% from my garmins estimate for it to be more realistic.

John.T

https://forums.garmin.com/showthread.php?t=5614
A lot of folks here think it under reads. I think I will just ignore my Kcal readings. I do not do much with them anyway.

SBezza

With the Garmin, it is hard to say if it under or over reads, it will depend on entirely what power that person outputs.

Just say 2 people exactly the same weight and age, and with similar MaxHR's, if one of them puts out 100W more power for the same HR he will expend alot more energy than the other rider. The Garmin would show very similar calories expended however, as it just doesn't know about each persons power output.

itboffin

SBezza wrote:

With the Garmin, it is hard to say if it under or over reads, it will depend on entirely what power that person outputs.

Just say 2 people exactly the same weight and age, and with similar MaxHR's, if one of them puts out 100W more power for the same HR he will expend alot more energy than the other rider. The Garmin would show very similar calories expended however, as it just doesn't know about each persons power output.

You're not helping my lust for a power meter much.

Stop it!

SBezza

itboffin wrote:

SBezza wrote:

With the Garmin, it is hard to say if it under or over reads, it will depend on entirely what power that person outputs.

Just say 2 people exactly the same weight and age, and with similar MaxHR's, if one of them puts out 100W more power for the same HR he will expend alot more energy than the other rider. The Garmin would show very similar calories expended however, as it just doesn't know about each persons power output.

You're not helping my lust for a power meter much.

Stop it!

Ah Just do it, I did the other day.

itboffin

SBezza wrote:

itboffin wrote:

SBezza wrote:

With the Garmin, it is hard to say if it under or over reads, it will depend on entirely what power that person outputs.

Just say 2 people exactly the same weight and age, and with similar MaxHR's, if one of them puts out 100W more power for the same HR he will expend alot more energy than the other rider. The Garmin would show very similar calories expended however, as it just doesn't know about each persons power output.

You're not helping my lust for a power meter much.

Stop it!

Ah Just do it, I did the other day.

John Stevenson

Garmin 500 and 800 Calorie consumption estimate is based on heart rate, so likely to be in the ballpark. Back-of-an-envelope calculations based on riding with someone using a power meter suggest it's within 10-15 percent.

Garmin 705 Calorie calculation ignores HR, and is therefore pretty much nonsense, to the point where we've always wondered why Garmin bothered with it.

schweiz

Agree that the 705 calorie calculation is meaningless.

I use Ascent to log my rides and that has its own algorithm to calculate calories burnt. It is surprisingly close to the PowerTap value.

The 705 value can sometimes be 50% higher than PT!

dexradio

Just done a couple of rides with my New Garmin Edge 800, and the calories it suggests are a lot more realistic by comparison to the 705/305 and Forerunner I use. Best calorie performance by Garmin so far in my "non-scientific" view. They have outsourced the calorie algorithm to a specialist company, just can't remember their name at the moment.

So far, I'm happy with what it reports. I don't have a Power Meter, but I'm sure that would improve accuracy even further.

Dex.

Butterd2

John Stevenson wrote:

Garmin 500 and 800 Calorie consumption estimate is based on heart rate, so likely to be in the ballpark. Back-of-an-envelope calculations based on riding with someone using a power meter suggest it's within 10-15 percent.

Garmin 705 Calorie calculation ignores HR, and is therefore pretty much nonsense, to the point where we've always wondered why Garmin bothered with it.

That does sound plausible. I have just moved from a Polar HRM which would generally have my using c. 900KCals per hour on a tough ride (I'm 16st). Went out with my new 705 on Sunday and on a relatively easy 2 hour ride it showed 2500 KCals. So I'm guessing 30-50% over the Polar.
I read somewhere else that Garmin cannot use the accurate Calorie algorithms as they are under patent/copy write. It was just on another forum so could be BS but again my experience seems to bear this out.