What do YOU need to do to have a major swimming breakthrough?"

It would be impossible to test the way you have presented. There are so many more variables as opposed to weight when losing 15 lbs and then gaining 30lbs. For example, gaining 30 lbs is most likely due to a lack of training. In my experience, which is in no way scientific, when I gained 15lbs of fat in high school one season, I still swam fast, even without much training. All of my coaches and others that I raced were amazed that with how I looked, and with how little I trained, that I could be as fast as I was. I think if we simply look at biomechanical and physiological principles, gaining fat will be offset almost entirely by increased buoyancy if all other physiological factors stay the same (VO2 max, anaerobic threshold, blood buffering properties, anaerobic enzymes, technique, etc.) If I were to accept that gaining fat causes one to have more resistance on their body, then gaining weight will cause one to train harder during practice, causing additional physiological adaptations, resulting in a wash speed wise. Then, when weight is lost, thus, reducing work during practice, times will get worse, another wash. Ande said: The thinner a swimmer is, the less resistance they require to slice through the water. Swimmers have to balance muscle and size. You could test it swim a fast 100 for time then lose 15 pounds and retest then gain 30 pounds and retest again compare the results

It would be impossible to test the way you have presented. There are so many more variables as opposed to weight when losing 15 lbs and then gaining 30lbs. For example, gaining 30 lbs is most likely due to a lack of training. In my experience, which is in no way scientific, when I gained 15lbs of fat in high school one season, I still swam fast, even without much training. All of my coaches and others that I raced were amazed that with how I looked, and with how little I trained, that I could be as fast as I was. I think if we simply look at biomechanical and physiological principles, gaining fat will be offset almost entirely by increased buoyancy if all other physiological factors stay the same (VO2 max, anaerobic threshold, blood buffering properties, anaerobic enzymes, technique, etc.) If I were to accept that gaining fat causes one to have more resistance on their body, then gaining weight will cause one to train harder during practice, causing additional physiological adaptations, resulting in a wash speed wise. Then, when weight is lost, thus, reducing work during practice, times will get worse, another wash. Ande said: The thinner a swimmer is, the less resistance they require to slice through the water. Swimmers have to balance muscle and size. You could test it swim a fast 100 for time then lose 15 pounds and retest then gain 30 pounds and retest again compare the results