I was reading the EXRX page on triceps and, unless I read it incorrectly, it said something along the lines of the long head working fully during extensions when the shoulder is externally rotated, but not working when it is internally rotated. My question about this is the following:
If I do a dumbbell skullcrusher with my shoulder internally rotated, will this shift emphasis onto the lateral/medial heads rather than the long head? Thanks!
I think that the rotation of humerus only affects the function of the long head, since it's the only one that acutally crosses the shoulder. But in theory it should be a bit more streched when internally rotated, and thus it can produce less force. This is only logic + anatomy, but yeah, it might be possible to shut out the long head more by rotation.