They differ at the fiber level, the synchronization of sequences, patterns of stimulation, etc. Rowing and swimming coaches commonly prescribe work at percentages of race-pace speeds with a resulting lack of appropriateness and benefit being obvious. Training responses are initiated, determined, and dictated by the brain. Without attention to the control of thought processes, which have not even been considered in this treatise, or attention to the encoding of exact movement patterns, many athletes will be trained inappropriately. Fitness is good.
Fitness is necessary.
But it is only valuable for athletic performance when it is developed in concert with mechanically efficient movement patterns which are encoded to high levels of automaticity in the athlete's brain. Training for fitness alone is likely to yield maladaptation. Training to energize the repetitive performance of good movement patterns is likely to yield rewarding improvements and in those with ability, performance excellence. As implied above, a complicating factor is whether swimming and rowing coaches know what are good movement patterns. When performance, such as swimming or boat speed is important, if athletes are not rowing or swimming with good technique, stop them, give them a rest, and start again with good technique.