Why Do Some Upper Arms Look Round And Others Look Rippy? (pics Included)?

Okay so look at this one below, the arms are nice and round and full.http://www.contactmusic.com/pics/m/i_am_…
In this one the arms especially the guy in the middle and right look not round and weird shaped, like the guy on the right has like a bend.http://imagecache2.allposters.com/images…
I’m just wondering the reason for this difference?

I Am Considering Jumping Off A 150 Foot Cliff And Trying To Fly By Flapping My Arms?

has anyone ever tried this before? Any tips would be great to help me accomplish this feat. I think if I pulled this off it would defeat any stunts David Blaine has EVER tried.