What are Physical Jerks in the book 1984?

In George Orwell's futuristic dystopian society, the Physical Jerks are a daily part of the lives of Oceania's citizenry.  The ubiquitous telescreens that enable the Party to both propagandize to and monitor the citizenry broadcasts every morning, at 7:18, a mandatory exercise program.  Nineteen-Eighty-Four, of course, depicts a totalitarian society in which the government controls every action and attempts to dictate every thought on the part of each individual.  Its apparatus of control knows no limits.  The constant propagandizing and the manipulation of terminology for the benefit of the Party are integral parts of that apparatus.  The physical conditioning of citizens, however, is not neglected, and the Physical Jerks serves as the regime's instrument for ensuring that all members of society are in the proper state of condition.  As Orwell's main protagonist, Winston, arises each morning, he is greeted by the harshness of the broadcast's dictates:

’Thirty to forty group!’ yapped a piercing female voice. ’ Thirty to forty group! Take your places, please. Thirties to forties!’ Winston sprang to attention in front of the telescreen, upon which the image of a youngish woman, scrawny but muscular, dressed in tunic and gym-shoes, had already appeared. ’Arms bending and stretching!’ she rapped out. ’Take your time by me. One, two, three, four! One, two, three, four! Come on, comrades, put a bit of life into it! One, two, three four! One two, three, four! . . .’  

Orwell's fictional society is one of absolute subservience to the will of the Party.  The Physical Jerks are but one component of the Party's strategy for total control.