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  1. #1
    Senior Member adxm's Avatar
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    Is wattage output directly linked to calories burned?

    I've upped my riding amount significantly in the past year or so and as a result am in much better shape. I use a Polar HRM that estimates calories burned from heart rate, and it has been giving lower and lower readings for the same ride and same pace, because my heart rate is lower. I also use a program that estimates calories burned based on speed, drag, climbing, etc, which I believe to be just calculating wattage output and deriving calories from that. Now it makes sense that wattage would be a much better indicator of calories burned (energy burned -> power out), but how much does your body's efficiency play a role in this? It seems plausible that if I rode with someone untrained for biking at 100W for an hour, I would burn less calories because I'm better tuned to the activity. Basically: am I necessarily burning the same calories by doing a given route at the same speed, even as this becomes less of a perceived effort for me to do so?

  2. #2
    Senior Member plin's Avatar
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    Good question.

    Power calculations are a better indicator of energy expenditure than HR monitor because energy output and HR are not linearly correlated. Here is how to calculate energy expenditure using power :

    Energy = power output x time.

    Power is measured in watts (W) and time in seconds, which gives an answer in joules (j). 1cal = 4.19 j,

    Example : 500 kj would be 119 kcal. however, the body is about 20 - 25% efficient, which means that you expend 4 - 5 times the energy, i.e., ~ 500 kcal. So basically in the end to get the number of calories spent in one hour, just take your average wattage for an hour and multiply by 3600(seconds in one hour) then divide by 1000 (to get the number in kilo calories).

    By the way, the best way to measure power output is with a power meter like PowerTap. I use a spreadsheet but it only gives an average for a climb and not instantaneous values. I envy people who can dish out over 1k for a PowerTap hub.

  3. #3
    OM boy cyclezen's Avatar
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    Quote Originally Posted by plin
    Example : 500 kj would be 119 kcal. however, the body is about 20 - 25% efficient, which means that you expend 4 - 5 times the energy, i.e., ~ 500 kcal. So basically in the end to get the number of calories spent in one hour, just take your average wattage for an hour and multiply by 3600(seconds in one hour) then divide by 1000 (to get the number in kilo calories).
    An interesting sidebar...
    Read, just a few days ago that Eddy Merckx, back in his prime underwent a test for 'power'. Turns out he was able to maintain over 450 watts for an entire hour (455 was his average) without reaching 'failure' (not sure that is the right term). Not done up to that point.
    Using your formula that's a prodigious 1638 calories for the hour...
    one would asume that subsequent hour record holders would be up around there as well.
    Anyone have similar comparo numbers for riders from later eras (Hinault, LEmond, Indurain, Armstrong, Ullrich, etc...)?

  4. #4
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    455 watts.
    Wow.
    I can do 225 or so.
    Maybe.

  5. #5
    Senior Member adxm's Avatar
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    That's a handy formula. Basically I was primarily interested in that efficiency component, and how much that actually changes with conditioning. From more detailed searching I see it's almost always in 21-23% range among trained cyclists.

    On a side note, I just got a V02 max test today as part of a medical study and reached exhaustion at 450 watts, after about 15 minutes of ramping up. I couldn't imagine holding that for an hour! I was in a world of hurt! For me, 'failure' at that point would definitely be the right term!

  6. #6
    OM boy cyclezen's Avatar
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    Quote Originally Posted by adxm
    That's a handy formula. Basically I was primarily interested in that efficiency component, and how much that actually changes with conditioning. From more detailed searching I see it's almost always in 21-23% range among trained cyclists.

    On a side note, I just got a V02 max test today as part of a medical study and reached exhaustion at 450 watts, after about 15 minutes of ramping up. I couldn't imagine holding that for an hour! I was in a world of hurt! For me, 'failure' at that point would definitely be the right term!
    Ive never had the opportunity to do a real test for 'power'. Would be fun to try, even well past 'prime', at 56, it would be fun to know... I have those silly Kcalorie numbers off the crap exercycles at the gym and could extropolate via that formula, but how close are those things anyway? Plus they are **** for 'position'. After 30 minutes I just can't wait to get off it...

    Back to 'Watts of the Titans' of the hour record...
    found this WAY COOL page , has great tech numbers for all the hour record holders
    the numbers just blow me away! and then I scroll down to Eddy's Numbers - gawd...
    I remember reading about all of them, since Ole Ritter's record in 68, its been great to follow these when they were announced. Shame they regressed the record back, tech innovation is part of the sport. it certainly doesn't negate Ole or Eddy's efforts. Cycling is about man and machine and as each improves, so should the distances...
    Anyway, my next fun project is to accummulate a full series of pics with each of the Hour Holders on the equipment they used - would be a fun comparo...

  7. #7
    bzzzz fuzzthebee's Avatar
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    Indurain averaged 510 watts for his 1 hr record, and he weighed 81 kilos.

  8. #8
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    Interesting formula: From Engineering Handbook

    Strong healthy young man HP=0.5-0.13log(t) t in minutes

    World Class Athelete HP=0.65-0.13log(t) t in minutes

    This is from 1996

    1 HP= 745 Watts

    For 1 hour SHYM= 201 Watts

    For 1 hour WCA= 312 Watts

    Yes calories burned are proportional to work. Remeber technique can massively improve efficiency

    I bet Indurain has great technique

  9. #9
    OM boy cyclezen's Avatar
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    Quote Originally Posted by fuzzthebee
    Indurain averaged 510 watts for his 1 hr record, and he weighed 81 kilos.
    This would be HUGE numbers ...
    ...sorry if this hijacks the thread... moved to another thread...
    Last edited by cyclezen; 11-17-05 at 09:23 PM.

  10. #10
    Newbie erhan's Avatar
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    Very interesting subject. I've been keeping a database of my rides, and after applying the formula, I found out that my average power is usually between 210 and 245 watts. That's better than I thought .

    I have a quick question. I also found that when I went riding with my girl friend my power output was about 70 watts. She was trying hard and I was just matching her pace. Does that mean that her hourly power average is also 70 watts?

  11. #11
    Senior Member DannoXYZ's Avatar
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    At that pace, yes... You can crank it up to 250 watts and see if she can keep up...

  12. #12
    sch
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    Makes you wonder what the wattage output was in the TT winners in last years TdeF where LA and 1-2 others were averaging 33.5mph over 50km or so courses.
    Steve

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