More on Break your Back from Infoplease:

• Break your Back - Break your Back (To). Make you bankrupt. The metaphor is from carrying burdens on the back. Source: ...
• William Shakespeare: Henry VI (Pt 2), Act IV, Scene VIII - Up Fish Street! down Saint Magnus' Corner! Kill and knock down! throw them into Thames!
• Dictionary of Phrase and Fable: B - Definitions, origins, and illustrative excerpts for words, phases, and literary allusions starting with "B"