We tend to forget this part of the Big Brother scheme, so let me provide a passage from Chapter III of 1984, as Winston's telescreen wakes him with "an ear-splitting whistle":
The Physical Jerks would begin in three minutes. ...The passage continues with material you're more likely to remember ("Winston could not definitely remember a time when his country had not been at war," "doublethink"), but do remember the Physical Jerks the next time someone on tv, especially the President, urges you to exercise. It's really quite unnecessary.
'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! ...'
... As he mechanically shot his arms back and forth, wearing on his face the look of grim enjoyment which was considered proper during the Physical Jerks, ....