So last night at the gym i work at, me and my training director ( one of my bosses) had a HUGE argument on how to do a preacher curl. I have always done my preacher curls ALL THE WAY UP and ALL THE WAY DOWN. When I come down my arms are 100% straight. He showed me this half rep bullshit where you only come down half way. Now only did this hurt my elbows but it I did not feel nearly as much activation from my biceps. Now this dude is on steriods ( he told me). The argument got so heated ( I tried my best to be the coolhead) that he almost fired me. Why? Because my view was different and I had evidence to back it up. Scott's vids ( YES, guys Scott Herman does count as a credible source), articles, etc.
The point is most times you shouldnt take lifting advice from a roider because they can get away with half reps and cheat curls.