Being one of those people with no patience or talent to even attempt editing any body meshes, i was a little disappointed when some meshes i liked didn't seem to be updated or worked on any more....
So i stumbled on this tutorial one day and i've been a conversion junkie ever since...
http://www.insimenator.net/showthread.php?t=41045It's much easier to fit clothing from a larger mesh onto a smaller mesh... so it should be possible to create athletic outfits from slim bodybuilder or bodybuilder outfits.
It took some learning when i first tried to do some for myself... but i got the hang of it pretty quick... but you'll need to keep in mind that you need to use a similar clothing mesh for what you're converting... I mean don't try to place a sweater and pants outfit on a clothing mesh for tank top and shorts... but try that if you want i got some great unexpected results when i did that...
Good Luck...
(hmm... i may even try to do a few athletic conversions myself today)