Well... your examples are not continuous tense. Maybe that's where your confusion lies. Continuous tense is made by using "to be" + (verb)ing. For example, "is improving" or "were having". Adding -ing to a verb is also how we make gerunds. This is what you see in your example. Gerunds follow prepositions ("in improving...") or they can stand as the subject or object of the sentence. They may even start a noun-clause which functions as the subject ("having a strong vocabulary base").

Verbo + ING, pode ser o participio do presente ou o gerundio. O participio se usa para construir os tempos " continuos" : I am talking to you now. I was talking to you yesterday... E o gerundio tem quase o mesmo papel como em português: I like playing soccer.. Doing it is very useful ... Se precisa mais explicações, estou à sua disposição K.

The ending "-ing" can also be used to nominalize verb phrases. For example, "to swim" is a verb, but "swimming" is a sport (noun). "To swim in the summer" is a verb phrase, but "swimming in the summer" is a noun phrase, that's why you can say "I like swimming in the summer."