On your way to BowerStone Old Town from the Market there are two houses with an alley in between.
Buy the house on the left and run upstairs.
Sleep in the Doublebed.
Afterwards it should tell you "Sleeping here has temporally improved your physique."
Go to "Abilities" and open "Strength". Keep selling your Physique Ability.
You'll notice that you earn EXP but your Ability will not go down. I have about 10M EXP from this.
This should Explain it.
http://www.youtube.com/watch?v=KVzCghEe2v8
*Many people have said it doesn't work.. I'm not sure why it doesn't work for some people.