I don't think it is the saddle most of the time. I don't think it is any one thing, but if it was,, I'd argue for crank length. I actually think it is a combination of things, including:
1&2 Crank length and too much drop - poor pedaling biomechanics
3&4 - Too narrow or too tight in cockpit - impinged breathing
5 - Insufficient time - Power comes up over time
6 - Posture, saddle discomfort, fighting the saddle etc - you've got to have saddle that reasonably comfortably allows for a full forward pelvic tilt.
And maybe 7 for some - Different devices measuring power at different locations on the bike
For me, I was absolutely equal from road to tri, after spending 20,000 miles riding aero over a few years. Extreme perhaps, but I think it is disingenous to claim that power will always be better while sitting up. It really does improve over time.
When attending to the above list, I have had very good success getting power with 3% going from road to tri. I really don't accept greater than a 5% delta with those I coach.
When I used to ride aero a lot, at a fixed load, I would always feel better when dropping down into the aerobars. With fit clients, they almost always have an opposite experience prior to being fit. Often, we are able to reverse that situation in the context of a 2 hour fit. Not always, but often. Eyes go wide as they lean over into aero and report that same load now feels easier. This is really the premise behind 100 degrees of hip angle in the FIST process.... lower or higher isn't as powerful. FIST is a great process, and the premise of a very narrow range of hip angles being the most powerful has proven true for me over several thousand fits. Crank length really ties the room together though, and this is something I have learned on my own over the last few years.
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