So, I’ve been messing around with a powertap for a few rides. Yesterday I did a one hour ride, diddling around on vacation in my family’s neighborhood. Average watts were like 158 , and covered 20 miles. For the first time I looked at the “E” measurement. It was 640 or something. Now, the powertap manual calls this a kilojoule. But it also says it is roughly the equivalent of a dietary calorie. But everything I have ever read says that a kilojoule is 0.239 calories (which would put my ride at 150 calories burned)
So, 640 seems a little high, but 150 seems low. What the frig? How many snickers did I burn?
Multiply the kJ by 1.038 to get kilocalories or dietary Calories.
So, 640 kJ = 665 food Calories or about 6 Reese’s peanut butter cups.
IIRC it is measuing the number of kJs your body puts into the drivetrain. However, it also mentions that conviniently the human body is something like 25% efficient at cycling. Therefore if the PT measured 1000 kJ, then your body actually burned 4000 kJ. Multiply by .23 and you have the number of calories. Since one multiplies by 4 and the other divides by roughly 4, you can assume kJ as measured by the PT will also be the number of calories, or at least pretty darn close to it.