FWIW I have been tested on one of those Trek/Bontrager computerized machines that measure pedaling efficiency. At the time, I was in my late 60's. I was told that a "good recreational rider" can pedal at 60% efficiency. Then the fitter said, "You're doing 85% with no imbalance in legs. How are you doing that?" I said, "I've never had a trainer but I've used rollers for over 30 years." He replied, "Of course."