Just a thought in case you ever get in a fist fight. Never, and I mean never, hit someone or anything for that matter with your thumb placed like because it's almost guaranteed that you will break it. I like how you lit this subject, although the focus seems a little soft on the fingers.
An OK photo (you might have not cropped it quite so tight at the bottom) but it looked a bit odd, so I tried the pose for myself. I found that the thumb is in the wrong place - it shouldn't be on top!
I don't think that is a very good way of showing strength, especially because the way you made your fist there is not particularly effective. Good technical quality on this pic though.