The Physical Jerks are a series of exercise routines required for members of the Outer Party. The telescreen monitors each individual's participation and criticizes them by name if they are not performing the movies correctly. This happens to Winston as he is attempting to exercise.
The Physical Jerks are just another way to show how pervasive Big Brother is and how the individuals in this society are ALWAYS being watched for any sign of deviation. It also shows the society's need to control every moment of the day so that people will not be alone and have time to actually think.
Doublethink is the necessary ability to hold two contradictory thoughts in one's head and believe them both to be true. Winston even notes that it requires doublethink to understand doublethink.
Basically, doublethink is a way of survival. If a person is not able to believe wholly what Big Brother says even in the face of contradictory information. Winston himself is required to change history on a daily basis and believe each new item. It is a way to control the minds of the people in society.
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.