1984 by George Orwell was first published in 1949. Since then, it has been printed numerous times. As a result, page numbers are going to vary depending on which edition you are reading. This selection is in chapter 3. In my edition of 1984, the 1963 printing by Harcourt Publishing Company, this passage is located on page 15. If you are using a different edition, I suggest looking for this passage a page or two after the start of the third chapter.
The passage here comes from the Physical Jerks that all the citizens of Oceania are required to take part in. At the same time every morning, a voice from the telescreen orders everyone in certain groups to work out in unison. The idea is to both keep the citizens of Oceania physically fit while also reinforcing the state's total control of everyone's life. Winston, who is part of the forties group, finds these exercises very uncomfortable as a result of the ulcer in his leg that prevents him from bending over to touch his toes. This is something that draws the ire of his group instructor, who thinks that Winston is too young to be suffering from such an infirmity and calls him out for it.