Calories burned in 100 mi?- Mtbr.com
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  1. #1
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    Calories burned in 100 mi?

    Anyone ever measured this with accuracy during the real conditions? I am curious as to what I burned in a recent race. I found a bunch of different calculators online but I wanted to know if someone has actually measured this.

  2. #2
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    I think true burn is impossible to measure. Everyone burns differently.
    It would be very cool to see a true figure.

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    This is a tricky one since its dependent on your base metabolic rate, time on course, and how you are measuring it.

    I don't really know how accurate the calorie counter on my polar heart rate monitor is. I'm not sure its really relevant from a performance aspect. You expend far more calories per hour riding than you can process. I do think its a neat metric from a curiosity standpoint, but I'm a nerd like that.

    To actually answer your question: for the Mohican 100 my computer said I burned 10,000 calories over the 12.5 hours I was on course. Granted, I'm a clydesdale and have a fairly h
    It's not about being better than others, it's about getting the best out of myself.

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    According to my Garmin heart rate monitor, I've burnt about 4,100 calories in each of the two 100 mile MTB races that I've done (one of which was Mohican). I feel like that number is a tad on the low side, but like thickfog said, I think any number that a HRM spews out should be taken with a large grain of salt. You give it your age, weight, and an average daily physical activity level and it spews out it's best guess at your metabolic rate.

    Sites like mapmyride and Strava usually line up to within +/- 10% of what I get on the HRM.

    A friend told me that the only true way to scientifically get an accurate caloric burn involves a lot of laboratory equipment.

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    Quote Originally Posted by Elan937 View Post

    A friend told me that the only true way to scientifically get an accurate caloric burn involves a lot of laboratory equipment.
    I think this involves measuring the O2 going in and the C02 going out, next to impossible to do outside a lab.

    You can make a reasonable estimate of calories burned if you know the power output over time ( i.e. avg watts ). A rough rule of thumb is

    calories burned = Time * avg watts * 4.0

    This is based on lab estimates that you burn 4 calories for every one calorie of work and does not include the base metabolic rate. All the calorie calculators in various exercise machines use some variation on this formula, many include some guess at the base metabolic rate based on your weight.

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    I know the devices we use out in the field are estimators but I was just wondering what some actual rides and devices had thrown out for numbers.

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    fwiw, on the road using my powertap: kilojoules = garmin's calories calculation*1.25

    kilojoules being a measure of energy expenditure, i'm not well versed enough to go into why kilojoules are an accurate approximation of calories burned but it's easy to look up on the web. andrew coggan says kjs*1.1=calories but i've also read where the relationship isn't as certain so take calories=kjs (which is what i do).

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    Quote Originally Posted by dvmullet View Post
    fwiw, on the road using my powertap: kilojoules = garmin's calories calculation*1.25

    kilojoules being a measure of energy expenditure, i'm not well versed enough to go into why kilojoules are an accurate approximation of calories burned but it's easy to look up on the web. andrew coggan says kjs*1.1=calories but i've also read where the relationship isn't as certain so take calories=kjs (which is what i do).
    If you look at the technical definition of kilojoule and Calorie ( i.e. what's printed on the outside of the box. )

    4.184 kilojoules = 4,184 joules = 1 Calorie = 1 kilocalorie = 1,000 calories

    Take estimated efficiency rates ( i.e. we burn 4 calories for every 1 calorie of power output ) and kilojoules of work is as good an estimate of calories burned as you're likely to get.

  9. #9
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    You can get a low ball estimate of calories burned simply with this formula.

    Meters in Elevation gain * ( Weight in kilograms of you + bike + clothes )

    If the course is relatively flat this won't work as well, but for up/down courses it will be at least that much.

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    Quote Originally Posted by bbense View Post
    I think this involves measuring the O2 going in and the C02 going out, next to impossible to do outside a lab.

    You can make a reasonable estimate of calories burned if you know the power output over time ( i.e. avg watts ). A rough rule of thumb is

    calories burned = Time * avg watts * 4.0

    This is based on lab estimates that you burn 4 calories for every one calorie of work and does not include the base metabolic rate. All the calorie calculators in various exercise machines use some variation on this formula, many include some guess at the base metabolic rate based on your weight.
    Once you have a lab test (Lactate levels energy expended and VO2 proportional to heart rate)....you intergrate the test data over the measured hear rate data....

    Human body is somewhere between 25% and 30 % Thermal efficiency (higher output lower efficiency)...

  11. #11
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    As others have said the garmin calorie is all over the place. Ive done 4 100m NUE races so far this year and each one was wildy different in the calorie burnt. From 3900 to almost 7000. I usually just laugh at it and know I need to go get some food

  12. #12
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    Few numbers I have from having a power meter on the bike. Can use the 1:1 kiloJoule to calorie conversion
    Shenandoah 100: 5,277 kJ
    Shenandoah 100: 4,271 kJ (cut out after 75 miles)
    Mohican 100: 5,435 kJ
    Crazy hard 100 miler (non race): 6,818 kJ
    24 hour Solo race (Won): 11,036 kJ

  13. #13
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    Quote Originally Posted by bbense View Post
    You can get a low ball estimate of calories burned simply with this formula.

    Meters in Elevation gain * ( Weight in kilograms of you + bike + clothes )

    If the course is relatively flat this won't work as well, but for up/down courses it will be at least that much.
    1000m * 150kg = 150,000.

    In either kCal or cal, this doesn't make sense.

  14. #14
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    5,200 and 4,100 for the two Leadville 100's I have done. Both times I came back at least 5 pounds lighter after a week at altitude with not much riding (other than the race) and lots of food, so I would guess that's an under estimation.

  15. #15
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    thanks for the numbers. Did Lumberjack 100 last week and had a blast but I didn't want to relace my powermeter into a mtb setup just so I could see the numbers.

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    Quote Originally Posted by No Agenda View Post
    1000m * 150kg = 150,000.

    In either kCal or cal, this doesn't make sense.
    Sorry, got my units wrong, insufficient caffein intake. A joule is 1 kilogram raised 1 meter in earth's gravity. So 1 kilojoule is 1 kilogram raised 1000 meters. So

    150 calories burned for a 150kg 1000m climb.

    that seems to be far too low. Oh well...

    - Booker C. Bense

  17. #17
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    Quote Originally Posted by bbense View Post
    Sorry, got my units wrong, insufficient caffein intake. A joule is 1 kilogram raised 1 meter in earth's gravity. So 1 kilojoule is 1 kilogram raised 1000 meters. So

    150 calories burned for a 150kg 1000m climb.

    that seems to be far too low. Oh well...

    - Booker C. Bense
    Geez

    Okay so you ignore the effort of pedalling the distance okay...

    So to get the force in Newtons you multiply mass times gravity 150 kg*9.8m/s2 and you get 1470 Newtons.

    To get energy you multiply Newtons times height...

    So you get 1000*1470 = 1470000 J or 1470 kJ

    So now you divide by the thermal efficiency 25% 1470/.25=5880 kJ burnt...

    Now we convert to kcal divide by 4.18 5880/4.18= 1406 cal.

    So I do about 1500 vert ft/hr 1000*3.281=3281 so that is going to take me 3281/1500=2.18 hours.

    That is about 1406/2.18=650 kcal/hr

    So it all goes around.

  18. #18
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    Quote Originally Posted by jeffscott View Post
    Geez

    Okay so you ignore the effort of pedalling the distance okay...

    So to get the force in Newtons you multiply mass times gravity 150 kg*9.8m/s2 and you get 1470 Newtons.

    To get energy you multiply Newtons times height...

    So you get 1000*1470 = 1470000 J or 1470 kJ

    So now you divide by the thermal efficiency 25% 1470/.25=5880 kJ burnt...

    Now we convert to kcal divide by 4.18 5880/4.18= 1406 cal.

    So I do about 1500 vert ft/hr 1000*3.281=3281 so that is going to take me 3281/1500=2.18 hours.

    That is about 1406/2.18=650 kcal/hr

    So it all goes around.
    Now I feel really thick... I knew I was missing something obvious.

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