How should I track workouts on a magnetic exercise bike?

Question

I recently bought a magnetic exercise bike to try and get extra training in around the family (normally do mountain biking using android app and mapmyride.com).

I am a bit confused as to how I can accurately log the workouts. The bike has various programs on it, which all work well. My issue is that whether you have it set to the easiest level or hardest it doesn't change the distance covered. Let me explain.

I can set it to manual for 5 minutes, at the easiest level. I would pedal at 90rpm steadily, it would give me the watts generated (around 25 I believe from memory). It would tell me I have gone 2.2KM (for instance).

I can then do the same but at a much harder level, i.e. 90rpm for 5 minutes. It would tell me I am doing round 90-100 watts around 4x as much, but the distance would be the same.

I am not sure how to record these training sessions so I can track my progress accurately.

Answer 1

Go with the watts. The nice thing is that due to the inefficiencies in pedaling, watts generated correlates very closely to calories burned.

The reason for the apparent discrepancy is in the perception. When you are on a bike, the distance traveled is a function is a calculation of gear inches. If you are set at X number of gear inches, and you pedal at 90 rpm, you will travel Y distance.

For your example, think of it this way. You are on a fixed gear bike, pedaling at 90 rpm for 5 minutes. You travel 3 miles (For instance). To achieve this, your output is 25 watts. Now, you come to a 3 mile hill at 5% incline. You maintain 90 rpm, and so in that 5 minutes your distance traveled will be the same, since your gear inches have not changed. But, to achieve this, you have to work 4 times as hard, so now instead of expending 25 watts, you have expended 100 watts. Same distance, same time, much greater work output.