In 1984, Physical Jerks are an exercise regime that Party members must carry out. These exercises are taught early in the morning, via the telescreen, and are organized by age group. Winston is in the thirties to forties group because of his age. While carrying out these exercises, Party members are expected to have a look of "grim enjoyment" on their faces because that is considered the "proper response." (See Part One, Chapter Three, for a full description.)
Doublethink refers to the practice of believing and accepting two contradictory ideas at the same time. In Oceania, the Party professes to be a Socialist government ("Ingsoc") and claims that democracy is "impossible," but at the same time, the Party calls itself the "guardian of democracy." This is an example of doublethink since these two ideas contradict each other.
These two practices are significant because they demonstrate how the Party controls its members. On one hand, the Physical Jerks provide an example of the Party's control over the body, while the practice of doublethink is all about control of the mind. Together, these practices ensure that the Party has complete control in all areas of a person's life.