Body by Qwark is an exercise book written by Captain Qwark. It first appeared in Ratchet & Clank: Tools of Destruction, where Qwark gave it to Clank as a prize, along with the Holo-Pirate Disguise to Ratchet. He said that it would give him "calves of a champion".
It apparently didn't sell well, as there are copies of the book that can be found as easter eggs in several games.
In Quest for Booty, several copies could be found near the shore of Hoolefar Island, near a golden stature of Captain Qwark.
In A Crack in Time, the book could be seen during the cutscene where the Plumber is pulling out items from a green pipe in Clank's subconscious.
In All 4 One, one could be found in the background during the cutscene after the Wigwump boss fight, next to a Dimensionator.
In Full Frontal Assault, a pile of them could be found on the Starship Phoenix II.
In Into the Nexus, it could be seen on the shelves at the gift shop of the Intergalactic Museum of History.