I recently bought a Tacx Flow trainer, which has a handlebar computer, with a 6channel RJ-11 cable between the trainer and the handlebar computer. The computer reads pedal frequency, power and speed, and is also able to adjust the trainer's brake -- thus two-way communication.
I have little to no experience in electrical engineering, but I thought I would buy a logic analyzer to see what I could find.
I think I managed to infer the GND and PWR (the computer gets power from this cable), and saw some patterns possibly related to speed and pedal frequency in two of the four lines (the two other lines were regular beats, and irregular, tiny signals).
I could not think of a way to progress further. Is this just impossible for a beginner to do?