Past-continuous-tense exercises are not physical exercises, or part of health and fitness. The past-continuous tense, also known as the past-progressive tense, is simply a tense in English. Therefore, past-continuous-tense exercises are written exercises: They, presumably, consist mostly of grammar problems which focus on the past-continuous tense.
According to English Grammar Online 4U, the past-continuous tense is a tense used in English to put emphasis on actions that take place in the past. For example, the sentence "I was reading my book" is an example of the past-continuous tense, because it places the emphasis on the action, as opposed to its completion. It is also often used to describe two actions that took place simultaneously, such as: "I was reading the book while she was cooking the rigatoni." Similarly, it can be used for an action that was taking place at a certain time, usually in reference to something that interrupted it: For instance, "While I was reading the book, Max called me."
Signal words of the past-progressive tense include when, while, as long as; plus, there are certain spelling changes that may take place, such as dropping the final "e" in a word like "come" so that it becomes "coming."