In regard to body build, I think I see a trend, towards more muscular.
In a way it's logical, because more muscle means more blood, and a quicker transition into anaerobic mode. More muscle helps to propel with more efficiency because it's easier to coordinate the movement when you're well within range of your strength abilities. Maintaining balance with ease.
Example, compare swimming with a monofin that is within your strength abilities, and one that is to big and stiff for you. In the latter you and your fin will be hopelessly out of balance, reducing your efficiency and distance.
In a way it's logical, because more muscle means more blood, and a quicker transition into anaerobic mode. More muscle helps to propel with more efficiency because it's easier to coordinate the movement when you're well within range of your strength abilities. Maintaining balance with ease.
Example, compare swimming with a monofin that is within your strength abilities, and one that is to big and stiff for you. In the latter you and your fin will be hopelessly out of balance, reducing your efficiency and distance.