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Calories burned according to computer...

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Calories burned according to computer...

Old 07-20-12, 10:54 AM
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surfer777
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Calories burned according to computer...

My computer on my bike tells me how many calories I burn during my ride. Generally speaking, are these numbers fairly accurate? Do they at least give you a ballpark estimate?

Thanks!
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Old 07-20-12, 10:55 AM
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PedalingFool
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Ballpark estimate...
I don't know of anything in the world that could tell you exactly how many calories you burn in any period of time.
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Old 07-20-12, 10:58 AM
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I am sure someone has a scientific answer, but I would say they are a rough guide based on some either simple math calculation or a complex one.

I assume your computer had you input weight, height, age (do you have a HR monitor)? So, the calculation is not going to measure some important variables like wind, road conditions, solo ride vs group, etc.

IMO -- yes, it is a ball park. The size of the ball park is certainly up for debate as well as the proximity to home plate.
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Old 07-20-12, 11:00 AM
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Originally Posted by surfer777 View Post
My computer on my bike tells me how many calories I burn during my ride. Generally speaking, are these numbers fairly accurate? Do they at least give you a ballpark estimate?

Thanks!
They're usually way off. Most computers don't take ascent/descent into account, nor do they know the wind conditions, nor do they know your bike weight, road conditions, etc. Honestly, I wouldn't even look at that field unless you get a power meter.
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Old 07-20-12, 11:08 AM
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my one hour training loop after work - intervals, warm up etc with reasonably high TSS score

garmin 500 alone - typically 1100 calories
garmin 500 w/ heart rate monitor - typically 900 calories
garmin 500 w/ HRM and Quarq power meter - typically 700 calories (the garmin has rider and bike weight in the calculation)

this is a loop i ride 2-3 days a week - sometimes on rain bike w/o the quarq and sometime i forget or lose (which i lost twice) the HRM.
so if for me if i get a calorie reading of just the computer i take 60% of that. and even that is a ball park.
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Old 07-20-12, 11:09 AM
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My garmin connect is always about 20% higher than my strava, so one of them isn't right. The number is just a guesstimate.
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Old 07-20-12, 11:20 AM
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Yeah I was thinking ballpark as well...especially since my computer didn't have me input my weight, bike weight, etc. But it sounds like typically the actual burned calorie count will be lower than what the computer reads, good to know.
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Old 07-20-12, 11:21 AM
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Some computers are more accurate than others. Older garmins can easily be off by 100% which isn't really 'in the ballpark'. Some of the newer garmins such as the 500 & 800 provide better estimates but for the most accurate estimates a powermeter is best.
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Old 07-20-12, 11:25 AM
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Yeah, completely useless. Not even a ballpark.
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Old 07-20-12, 12:15 PM
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I'd say an uneducated guess at best for my Cannondale IQ300. I only had to input my weight for the kcal burned function. Not even remotely enough data to compute the rate burned. Not what I bought it for, though.
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Old 07-20-12, 12:21 PM
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My own experience with two different systems demonstrates that they are a rough tool, but useful in an over-all-grain-o-salt-but-focus-on-other-metrics sort of way.

Both technologies show that there is a proprietary* 'Fudge Factor' that relates caloric expenditure linearly to the product of Average Heart Rate and Trip Duration. The linear relationship suggests to me that for every [all, maybe?] weight and age configuration[s] there is a Fudge Factor that links human output to calorie expenditure.

Maybe we should look for truth in the heart rate and duration data rather than in calories as indicators of effort expended in pursuit of fittness. Well lads and lassies, that's my drum-beat at any rate.

* - I asked...they told me it was a trade secret.
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Old 07-20-12, 12:29 PM
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My Garmin 500 guesstimate was halved once I added a heartrate monitor. Unfortunately, my post-ride beer drinking has remained fairly constant.

Last edited by unionmade; 07-20-12 at 12:30 PM. Reason: forgot a word
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Old 07-20-12, 12:32 PM
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I find that my garmin always reads ultra high, near unbelievable numbers. Strava has much more reasonable numbers. Its all a guess though
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Old 07-20-12, 12:51 PM
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Originally Posted by PedalingFool View Post
Ballpark estimate...
I don't know of anything in the world that could tell you exactly how many calories you burn in any period of time.
Power Meter.

Good power meter will give KJ put out +/- 1-2%.

A calorie is equal to a little more than 4 KJ.

Then you have to figure how efficient you are in converting calories to KJ. Lab tests show that cyclists are 18-23% efficient in converting calories to KJ. Take the midrange of that, and you get 1 KJ = 1.1 calories, with an accuracy of +/- around 5%.

So the Powr meter can't tell you exactly how many calories you burned, but it can within about 10%.


Comparing power meter results to non power based estimates, and the non power based computers are almost always high, sometimes as much as 100%.

Some of the newer ones, utilizing HR, such as the Garmin 500 get closer, but still read high.
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Old 07-20-12, 01:08 PM
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Originally Posted by valygrl View Post
Yeah, completely useless. Not even a ballpark.
Agreed that the calories burned is not the same as the true number. But as far as useless, I think it depends what you want to do with the number.

I have very successfully used the calories burned from a Polar HRM (so it uses heart rate, age, gender & weight) to track calories to lose weight. What I did was set the weight in the HRM to 25 lbs below my actual weight. As I got closer to my target, I made it 15 lbs below. I would also adjust the final number downward based on the type of ride (or hike or swim or run) I had done. If it was a long easy ride with slower friends plus a couple of stops I would adjust downward about 20%. If it was a hard ride with attacking hills and pushing down the other side I would adjust downward about 10%.

Over the course of several weeks and months it didn't matter whether any single recording was correct. What mattered is that it gave me usable estimates to adjust my diet accordingly. I lost 40lbs with the HRM's calorie count being one of the inputs I used. (That I am now once again trying to drop 20-25 lbs is testament to what happened when I stopped tracking everything, but that story is for a different thread.)
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Old 07-20-12, 01:27 PM
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Originally Posted by surfer777 View Post
My computer on my bike tells me how many calories I burn during my ride. Generally speaking, are these numbers fairly accurate?
No.

Do they at least give you a ballpark estimate?
No. It can be high by a factor of 2 or more.
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Old 07-20-12, 02:58 PM
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Just put your weight, age, activity, and calories per hour into Dr. Google and it will return a vague answer. Add a grain of salt and then compare the results from your bike computer.
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Old 07-20-12, 03:03 PM
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Edge500/800 use a pretty fancy algorithm if you have a hr strap. On days im on a bike without my power meter the numbers are pretty darn close to the days when I do have a power meter, so their HR based guess must be pretty good for me.
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Old 07-20-12, 03:05 PM
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Edge500/800 use a pretty fancy algorithm if you have a hr strap. On days im on a bike without my power meter the numbers are pretty darn close to the days when I do have a power meter, so their HR based guess must be pretty good for me.

As for people saying it's not ballpark, I don't see how they can say that. I don't see anywhere where you've told us what computer you're using. An edge500+HR strap is definitely in the ballpark.
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Old 07-20-12, 03:50 PM
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i wear a heart rate monitor, which i think does a pretty good job of calculating calories burned based off of your age, weight, fitness level (i guess based off of resting heart rate or something...there's a "fitness level" thing on my polar heart rate monitor where you lay down for a minute and it outputs some number), and of course your heart rate over time.
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Old 07-20-12, 03:52 PM
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Originally Posted by jmX View Post
Edge500/800 use a pretty fancy algorithm if you have a hr strap. On days im on a bike without my power meter the numbers are pretty darn close to the days when I do have a power meter, so their HR based guess must be pretty good for me.

As for people saying it's not ballpark, I don't see how they can say that. I don't see anywhere where you've told us what computer you're using. An edge500+HR strap is definitely in the ballpark.
I have a Garmin Edge 500, heart rate strap, and Powertap.

On easy rides with a heart rate strap the Garmin is 20% high versus kilojoules adjusted for the minimum observed cycling efficiency. On a two hour ride at an endurance pace that's 200 Calories. That's like three eggs scrambled (what some people would call breakfast) or nearly 1/4 pound of lox on your bagel.

Without the heart rate strap it's 100% high.
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Old 07-20-12, 04:49 PM
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Exercise is supposed to elevate your metabolism. Is the reading from a Garmin 500, for instance, the calories burned during exercise or does it include the effect of increased metabolism?
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Old 07-20-12, 05:00 PM
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My Garmin 500 appears to be the most accurate, and conservative, machine or computer I've used. I average right around 30 C per mile in a normal workout, where I spend about 1/3 of the time in zone 4. I weigh 220, and would seriously question any figure much above 35 C per hour, unless that person was practically a pro athlete. A lot of machines at the gym give you absurd figures like 800 to 1000 C per hour. Their computers must be designed by the same people who work out clothing sizes in department stores.
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Old 07-20-12, 05:09 PM
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How does a power meter measure metabolic activity? I.e. if you're working hard then you're breaking harder and what not. How is that accounted for? I would guest from a biological standpoint all a power meter is giving you is what your legs are putting out - not your whole system.
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Old 07-20-12, 05:56 PM
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Regular computers without HR are a wild ass guess. Especially if you're drafting. With HR makes it wildly more accurate. Strava doesn't do too badly either, although it also has no hope if you're drafting. Power meter is the only real way to know, but HR isn't bad at all, especially with a good algorithm and correct max HR/weight/etc.
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