Are you a triathlete on the go who also wants to do more writing in your life?
One solution could be a program for dictation – so that you can record your voice and have it turned into words that you can edit later on.
It would certainly only work during certain workouts – maybe a light run or light cycle on the trainer. Or perhaps you can incorporate it easily into other areas of your life.
An app was recently recommended to me called Dragon Dictation. I have not used it and have no connection to it, but it may be a place to start looking if this is a tool you want to incorporate into your life.