The Relationship Between Orientation of Fibers and Muscle Function

The internal moment arm is the perpendicular distance to that line of action from the joint center. Orientation of fibers really has enough almost nothing to do with the either of the other two. When you look at the real delts internal moment arms throughout motions, their relative moment arms are the same. The only way muscles could produce force when they're parallel to the external line of force would be if it were longitudinally. And I like they don't produce force that way. It's always laterally.