I just finished working on a little prototype, based on an inexpensive RGB keypad & microcontroller - I give you the “SUFpad”!
This little thing connects via a USB cable to your PC and lets you control your workout from the palm of your hand.
If anyone wants to try this at home, the CircuitPython code is here.
The next project I am looking at will do away with the keyboard entirely, instead there will just be a clickable spinning knob with RGB LED lighting that can sit on your stem or headset top-cap - click to switch between ERG & level mode, rotate to increase/decrease difficulty, double-click to pause/play. It will be interesting to see if that works as a user interface…
More than you,