which parts? (assuming breaststroke / freestyle and doing laps)
I love how br3aststroke is censored.
and I didnt know trains could swim, choo choo!!
for swimming, it depends on what stroke you use.
for front crawl, its quite a composite exercise that trains much of your upper body which are your pects, lats, teres, trapez.
bre@ststroke not so much on upper body already.
Deltoids(shoulders), pectorals(chest, especially for breast), triceps(pushing motions), quadriceps(legs push out), glutes(ass muscle).I forgot to say your lats(back muscles)especially when you stretch your arms foward and the abdominals as well
Many other parts..