It is a very common pitfall, particularly among rowers and scullers, to assume that more fitness inevitably means more speed, because it usually does, if you only consider a single athlete in comparison to himself. Simple math, right? If I get fitter, I’ll get faster! So far so good. The theory falls apart, however, when you look at two equally fit athletes, one of whom is well-adapted to the more subtle aspects of the sport and the other of whom has limitations that have nothing to do with fitness, but rather technique, confidence, temperament, neurological factors, and so forth. Something I’ve learned from being around competitive swimmers is instructive here.
I swam in high school, for a single season. The team was pretty improvised - we frankly were not very good, not very dedicated, and not very well coached. That said, by the end of the season we had learned enough to have some sense of why we weren’t very fast in the pool, what it was that we lacked, and how we might go about moving in the direction of swimming better. One phrase that stuck with me was "ride the glide," which pointed to the idea that swimming was as much about streamlining the body and allowing it to "run" while under the somewhat periodic application of propulsion. The interplay of propulsion and glide was intriguing, and most of us were limited by our rudimentary understanding of how to actually make it happen. It made sense in an academic sort of way, but we couldn't really feel it in the pool, or at least not the way that better, more accomplished swimmer could and did.
Many years later, after I had rowed in college and learned to scull, I got back in the pool - partly because I had developed an interest in using triathlons as a cross-training and competitive outlet and partly because I had a recurring back injury to keep at bay. I was training a few times a week with a masters group, some of whom had swum competitively in high school and/or college and some of whom, like me, who had not. What swiftly became apparent was that the people who were real swimmers had a phenomenal ability to go further with each stroke than those who were not. By far the biggest difference between a fit person who swims and a real swimmer is the number of strokes it takes each to get across the pool. It would be hard to overstate how dramatic the difference was - the “real” swimmers might take 11 or 12 strokes to cross the pool, while the fit people who were not swimmers might take 18 or 19. And it clearly wasn’t a matter of physiology - some of the non-swimmers were demonstrably fit people - people who were winning races in their chosen sport at a very high masters level, 2:30 marathon runners - while some of the folks who had been collegiate swimmer had clearly gone to seed, so to speak - they weren’t that fit and could still easily go faster than the fit non-swimmers. And you see that happen and you scratch your head and you almost inevitably have the "wow - how do they DO that?" reaction. So then you try to do it yourself, and you take a shot at getting across the pool in fewer than 20 strokes and you get there in 18 or 19 and you experience a similar reaction - you still don't really get it. "I tried really hard to get more propulsion per stroke, and I tried really hard to streamline myself and glide further and I can now imagine getting across the pool in 11 strokes and I did it in 18 and now I can imagine doing it in 17 but how in holy hell are they doing it in 11? And at that point you have a moment of truth in which you either decide that you're not ever going to get it to the extent that real swimmers do, or you accept that the road to figuring out the subtleties of the sport is long and requires more than just fitness and you're just going to have to keep chipping away at all of those unquantifiable subtleties as you make your journey from 20 to 11. Good luck.