When learning Pose running technique, and athletic technique in general, a lot of people get caught up in which muscles get used and how much. My advice, which I received from Dr. Romanov, is not to worry about which muscles you are using. Instead worry about achieving the correct pose or position. If you are in the correct pose, then you are using the right muscles.
After all, this is running not body building. Body builders worry about specific muscles because they are using non-functional single joint exercises to isolate and work on specific muscles. Running is a functional exercise, and as a functional exercise, your body needs to work as a system. So it is not helpful to try to break down the exercise by muscle group. Yes, of course some muscles are getting more emphasis at different points, but they are not working as an isolated unit apart from the other muscles in your body, but rather in coordinated fashion to accomplish a specific task with the least amount of effort.