mtalinm

well I thought I was burning 50 calories per mile at my weight based on a number of tables I had looked at include this one: https://www.bicyclesource.com/body/tr...urn-rate.shtml

but for the first time today I went on a ride with a buddy of about the same weight and who had a power meter. we did 36.5 miles with 1200" of climbing at an average speed of 14mph. my rule of thumb would've said 1800 calories burned, but his power meter said 1400. that's more like 40 calories per mile.

funny thing is that I have my Garmin thinking I'm 100# lighter than I really am (i.e. target weight) and it came up with 1900 calories burned. maybe I have to tell it I'm a 98-pound weakling??

Mr. Beanz

I often wonder how accurate those things are. I did a ride with a guy, 60 miles, 6100ft of climbing, averaged 13.79 mph and he said we burned 6000+calories according to his gauge (Garmin/HR?).

Then I went alone, 7200 ft of climbing, 12.0 average, 59 miles. Wonder if I'd be a skinny guy if I did these rides more often. I was 230 lbs. Maybe I should look it up.

jethro56 

My garmin tends to agree with the calorie stuff on the machines at the Y. Maybe they're all wrong. I just use the data to quantify the volume of work I do. The absolute number doesn't really mean anything. Past experience shows that I can expend so many calories/day. So many calories/week. If I get to my weekly goal I get the rest of the week off. My goal is to slowly increase the number. It could be 10,000 or 100 doesn't really matter. Next week i'd try to hit 10050 or 105. By the way,an average on it's formula is 52 cal/mile. If I go slow it might be 40/mile if I go faster it might be 65/mile.

socalrider

Most HR's and Garmins especially are too high on there Calories calculations.. I think they want us all to feel good.. Polars are very high, the only one I found right in line with effort are the Suunto Heart rate monitors..

40 cal per mile is a little high.. If you are riding at 60% of HR you will be in the range of 8 cal per minute.. 16 cal per minute is on the top end of calorie burn which is achieved at 90% + of MAX HR effort..

sstorkel

Calorie calculations based on HR alone, or random numbers punched into somebody's website, are never accurate. Numbers based on measured power output, such as those obtained from a PowerTap or Quarq power meter, are supposed to be reasonably accurate.

Haff

Power measured at the hub will be a great indicator of the power of moving the bike forward. What it wont be is a good indicator of the power needed to repeatedly redirect the huge legs of a typical clyde or athena. There is a significant inefficiency of moving the human body parts around that doesnt end up in moving the bike forward. Its energy spent for the purpose of biking, not just living, so it should be included in the total count. Problem is... I dont think anyone has a clue how to calculate it for a given person. So screw it. Just measure distance traveled. Its unambiguous, easy to measure, easy to train against, and still gives a decent qualitative assessment of how much work was done.

jethro56 

The large calorie, kilogram calorie or food calorie (symbol: Cal)[2] approximates the energy needed to increase the temperature of 1 kilogram of water by 1 °C.
So if you want to measure calories accurately you need to be immersed in a known amount water and measure the temperature change while biking. Not very useful.
If fact, almost all electronic devices used in measurment involve some sort of model that predicts something based off of a change in electrical state of a circuit. The best one can hope for is that the change is repeatable.

Does garmin and polar want to make people feel better while using their devices? Maybe and that isn't all bad.If their devices help keep me motivated then I don't mind.More likely their prediction is based on someone that is not as efficent as I.What I like about their devices is that they allow be to quantify my workload over different activities, to avoid overtraining and to challenge me to higher levels of fitness.

Haff: if distance is what motivates you to ride then distance is what you want to measure.
Mr Beanz: If beating skinny guys with garmin devices motivates you that's great.

Wogster

I think a lot of these machines are inaccurate and most, if not all, of them do err on the side of over enthusiastic. I think this is to encourage the user, in that if you see 1800 rather then 900 you will be encouraged to exercise more. Power Meters though, measure the energy to move the bicycle, but do not measure the energy needed to move the engine parts. This is compensated for with calculations based on an average person. This average person is probably a 1.7m tall male who weighs 65kg, so the actual calories burned by this average person is probably a little short for a Clyde. I think realistically the only way to get an accurate measurement is to get a personal physical assessment done by a specialist who does this for professional athletes. You then run the same tests with your meter and compare the results, you will then have your own correction factor so when the machine says X calories, you apply your correction factor to get a real calorie count.

Really though whether it's 1800 calories or 1800.0000000000000001 calories doesn't really matter, if your concern is weight loss, and the weight loss ticker indicates that currently, it is, then you want to underestimate the calories burned and over estimate the calories consumed, unfortunately the machines tend to over estimate calories burned and many food calorie sites tend to under estimate calories consumed (it's not the sites fault it's often the portion sizes are not specific enough), and people are caught in the middle wondering how you can burn 4000 calories a day, eat 2000 calories and end up not losing weight when you should be losing nearly 5lbs a week.

So, if we hold to this rule of underestimating burn, and over estimating consumption, then for your Garmin, apply a correction factor of .75 and for the food calorie site apply a correction factor of 1.25 and set your targets for the corrected numbers. If you find that you lose more then intended you can adjust the correction factors.

sinclac

I am willing to bet not even close i weight 192lb and on that 36 mile ride i would burn 700 or so calories, i know this because i wear a bodybugg this is how i lost 100lb.
I know what i burn and when i burn it

Mr. Fly

Err...a calorie is equivalent to 4.2 Joules and by extension, a Calorie is equivalent to 4200 J. Those amounts can be measured quite readily by a lot of devices that does not involve immersing in any liquid. Just because the energy unit is defined one way does not mean one is stuck and cannot use equivalents. I don't know of anyone who routinely measures small lengths with a laser and very accurate clock (outside a lab), for example.

Powertaps and other power measuring tools use strain gauges, and these are devices have known and established characteristics. Industry use them all the time. I don't know if your apparent distrust is warranted.

chasm54

The algorithms used by these things vary. My old garmin 305 used to tell me I was burning 50% more calories than my new garmin 500 does. The latter is, evidently, much more accurate. If I'd been burning calories as fast as the 305 said I'd have been thin as a rake. but even the new one, based as it on HR, will be approximate at best. Powermeter figures will be much more reliable.

jethro56 

I wouldn't use the word distrust. I'm a retired computer programmer with my field of expertise being industrial automation. I'm well aware of the pro's and cons of measurement devices. Much of my work was done in converting the raw data from a measurement device to information. Information is only useful if it leads to a change in behavior. Take for example a temperature guage in your automobile. You can have the most accurate guage available but if you don't know what temperature your automobile should run then a innaccurate warning light would better serve you to identify a problem.

I have much to learn about bicycles. My uniformed opinion is that a powertap wheel and a garmin/polar device serve different purposes. I would imagine a powertap owner would be more interested in changing his behavior to increase speed. While increasing speed is of interest to me as a garmin owner, the information I seek is actually to know when to hold back. My desire is much more than my ability.

tabriz

Hi, I have a Bodybugg, too. I've heard they aren't as accurate for biking as they are for walking/running. But you disagree with that? How do you know it is accurate? I'd love to try mine for biking but thought it wouldn't really tell me anything.

Tabriz

sstorkel

Here's one PowerTap owner who's just as concerned about losing weight as he is about increasing Functional Threshold Power (FTP). Speed? Honestly, that number is so meaningless my Garmin isn't setup to display it these days. The PowerTap is, by the way, a great device for knowing when to hold back. I've crushed several riding buddies pretty effectively by keeping my power output close to FTP while they're burning the candle from both ends during the early part of a ride...

gbg

That sounds about right, with my experience with my powertap. You did 2.6 hours ( with some climbing) so that is about 538 cals per hour, (I like to use cals/hr) which is pretty good. I think to get to 5-600 c/h is a fairly hard effort. I am assuming you are on some sort of MTB not a skinny tired road bike, since that has less rolling resistance etc which would result in a lower cal burn. To get to 7-800 cals per hour that is race pace and I don't think most people could keep it at that pace for an hour.