I've got a Level 12 gnome paladin who has been pretty diligent about boosting the Athletics skill and I don't think I've ever seen a single stat increase. AFAIK the only stat increase I've gotten is one from eating an ogre corpse.
It might not be athletics - I also haven't seen any STR increases from being burdened/strained (strength: 16 out of potential 23) - I'd have expected to see one.
Toughness only 14, Dex lower - so within the range where I'd expect Athletics to help.