Originally Posted by
zacster
I use RWGPS as my main tracker and I can calculate the calories in a spreadsheet that matches their calculated value exactly. They use 25% as the human efficiency number, but when I plug your numbers in I get a much lower number for calories, 394. kjoules should always roughly equal calories as the .239 and 25 mostly cancel out. Something isn't right there.
B20×(B21+B22÷60)×60÷1000×.239006÷.25
Where
B20 = avg watts
B21 = Minutes
B22 = Seconds
The calc is a little convoluted as written only because I originally wrote it just for minutes, but then included the seconds for accuracy. It is Watts * (minutes + seconds/60) then times 60 again to get to seconds to get to joules. Divide by 1000 to get kJoules, then apply conversion to Calories and factor in human pedaling efficiency.
413 kJoules is right, but the Strava efficiency looks to be about 20%, where the RWGPS numbers you get use 15%. Is that number part of a setting somewhere that it could be so different? I don't remember that, I probably wouldn't have known what it was anyway as I've been using it for years an only recently looked into the calc.
Is your power accurate? Are you using a power meter or is it estimating power based on HR? When I ride my commuter bike without the power meter it uses HR to estimate calories and power and it is way off. In order for it to be closer to accurate you need VO2 Max.
I occasionally glanced at ride calories, but I don't pay attention to them.
I have a Stages left crank meter, that both matches up reasonably well with my Kickr's watts, and with online bike calculators for watts on steady climbs.
Todays' ride on rwgps: 1172 kjoules, 1479 calories. Still high calories.
Browsing my profile, I see this note, and two links:
Power output is estimated from calories burned, assuming a 24% efficiency. As a result, the numbers produced are not perfect – however, they are accurate enough to be useful. In addition to the information we ask for here, we use the duration of your ride and your average heart rate. As a result, a ride must have heart rate data in order for calorie or power data to be available.
http://www.braydenwm.com/calburn.htm
http://www.braydenwm.com/cal_vs_hr_ref_paper.pdf
~~~
I'm 70, with the corresponding lower heart rates. I skimmed the calories vs heartrate paper (which is from 2005), and noticed a formula that takes age into account. perhaps that's why? I'm not sure why old riders would burn more calories for the same watts output -- generally less efficient in the food calorie conversion?
That's all I know.