John, these are excellent questions. Since Tricia didn't respond, please allow me. The research done by Dr. Alberts shows that people on a tandem have following distribution of energy output: 75% of the energy is provided by the captain on the front and 25% of the energy is provided by the stoker on the back. For whatever reason, the cadence is the key. The patient must be riding at 60 to 80% of his/her maximum heart rate and maintain the cadence of 80 to 90rpm. The captain can adjust the resistance until the stoker is riding at the proper RPM and heart rate.
Obviously a solo cyclist is providing 100% of the energy. The key still appears to be to maintain the proper cadence of 80 to 90rpm or higher if the proper heart rate is maintained.
I hope this helps.