sexual hormone binding globulin binds to sex hormones like testosterone rendering them useless, essentially. The testosterone that really means anything in a muscle building sense is the "free testosterone" -- that which isn't bound up by SHBG.
I also have enjoyed green tea preworkout -- I love the thermogenic effect. I much prefer having a good sweat going when I workout.
I have no idea to what extent green tea may increase SHBG, but it may be of interest to some of us.