Since I am a bodybuilder, and I train for overall muscular mass and development, I target my fast twitch fibers, which are what gives your muscles both strength and size. Since fast twitch A fibers are the dominant fibers for size increases, while fast twitch B fibers are dominant for strength increases, I train specifically to target my fast twitch A fibers, and do other things to encourage my fast twitch B fibers to take on the characteristics of my fast twitch A fibers.
Since slow twitch fibers cannot take on the characteristics on fast twitch fibers, I avoid any type of training that would switch emphasis to the slow twitch fibers. Activating my slow twitch fibers not only will not provide benefit to my size gains, it will actually have a negative effect on my size gains, since the hypertrophy of slow twitch fibers leads to the atrophy of fast twitch fibers.
In keeping with achieving my goals, when everything is taken into consideration, and I end up with my perfect routine for maximum mass gain, my actual time in the gym rarely lasts longer than 30-35 minutes.
