What makes comparative studies so difficult is that it takes a long period of adaptation and coaching to use particular equipment. I spent my first year of training on a modern road bike mostly learning how to pedal properly with clipless. I clearly remember the day when I made three consecutive perfect pedal strokes on a MUP. A few weeks later, I pedaled properly continuously for 100'. 15 years later, I'm still working on it.

One of the fun things about riding a mixed tandem is that we can feel each other pedaling. It's kind of like dancing together to exhaustion. So when one of us lapses into "push-down," which is easy to do, the other says, "Pedal circles!" When we both do it right, I don't think the bike accelerates noticeably, but it climbs almost effortlessly at the same HR. If you're doing it right, the bike should float up the climb. Yesterday, we climbed for 4 hours at 90% of LT and our legs aren't sore today. Almost bonked, but ate our way out of it.