There are really three choices: bent arm, locked out arm, and arm almost fully extended but not locked out, which is what I prefer. I teach archery to kids, and often find that girls hyper-extend their arms. In other words, when they fully extend their arms, their arms bend back the wrong way a little. This almost guarantees that the string will hit their arms, and since they can't really extend their arms in a straight line, I recommend they bend their arms a little. Rick Welch recommends you bend your arm a little. Many longbow shooters bend their arms. If it works for you, then do it.