How did beethoven's musical composition during the "middle period" of his life differ from his other periods?

I have read that the music that Beethoven composed in his "middle period" differed from the other periods of composition of his life as it placed a strong emphasis on dynamics and also furthered the scope of the clical period of compositon at the time. Yet I would like to know how his music placed a strong emphasis on dynamics and how his music furthered the scope of clical music, if at all.