How can I accurately measure the calories burned while using my bicycle? My bike computer tells me how many calories I have burned. But it has no cadence meter. The only measurements it has are my weight, distance, instantenous speed, and time (and all information it can derive from that). Using the GPS on my phone, and the software from Sports Tracker on the same route, I got wildly different results. The information on sports tracker yielded about 1.5 times more calories burned then on my bike computer. Now, the GPS has a little more information, like altitude, but the ride was mostly flat. To add to that, there was an elevation drop over the entire route, so I don't know why it would say I burned more calories. Do these devices use standard formulas, or do they just make stuff up?
Is it even possible to accurately measure the calories burned? It seems that even if I had a cadence meter, there would still be a lot of variables. Wind speed would make a big difference. If you pedal with the wind at your back on a fixed gear, going 30 km/h, you are going to use a lot less energy pedaling the same bike at the same speed if you are going into the wind. Note that in both these cases your cadence would be the same, but your muscles would be working much harder in the case where you were working against the wind. Same could be said for things like hills, although this could be done with altitude, although I'm not sure how accurate you could get. Road conditions could also make a big difference, not to even get into the riding characteristics of the bike.