Power Calculation for 50 Calorie Bike?

At Crossfit, the workout of the day was a 50 calorie workout on the stationary bike (Concept 2 BikeErg) for time. If I did it in 2 minutes, that’s a calorie burning rate of 25 cal/min. I should be able to convert this to watts, which is joules per second, so I can compare it with my Sufferfest results.

According to the internet, there are 4184 joules in a food calorie. So, I burned about 200,000 joules in about 120 seconds. This is 1750 Watts. According to my Sufferfest 4DP results, I’m not even close to putting out 1750 Watts for two minutes.

Can anyone explain the discrepancy?



Okay, there’s a few things to think about here.
First, calculating calorific burn is a guess at best.
Second, human efficiency is poor (~25%) so the actual power output for a calorie is closer to 1000 joules, you burn ~4000 but only put a quarter of that into the pedals.

The equation you’re looking for is a re-factoring of the following, which is used to calculate calorie burn…

Power x Time(S) / 1000 = Calories

So for you we’ve got:

Power? x 120 / 1000 = 50

Let’s simplify:
Power = 50,000 / 120

Therefore power = 416.66 recurring

417w for 2 minutes looks a bit more realistic, doesn’t it?


Thanks! I was guessing about 400 Watts.