Just for the record, an ERG (short for ergon, a Greek word meaning "work/task") is a unit of energy and mechanical work equal to 0.0000001 joule. It originated in the centimetre–gram–second (CGS) system of units, symbol "erg". It is not an SI unit.
In other words an erg is approximately the amount of work done (or energy consumed) by one common house fly performing one "push up", the leg-bending dip that brings its mouth to the surface on which it stands and back up.