Hello, I've been taking propecia for the last year with good results.
I'm trying to add some muscles and body weight by working out and body
building trainings (I'm not taking any supplements or steroids). Can
propecia prevent me from developing more muscles? is there any
research about propecia and body building/ sports training?

FYI...Propecia messes with your testosterone.  i would get your levels
checked to make sure they are intact..seeing u need testosterone to
build lean muscle.  as a previous user of propecia...for 9 years i was
good until my levels of testosterone were so low that it impacted my
sex drive...screw that! quit taking it and levels are back up.  i
would keep an eye on your testosterone levels. good luck

Propecia is an androgen hormone inhibitor used to treat male pattern
hair loss in men ONLY.
http://www.drugsinfo.us/propecia.html