I think that this is a case of more information -> overthinking -> confusion. Just train for the kinds of things you want to DO with your muscles, and prioritize the kinds of ACTIVITIES you enjoy and benefit from. The correct mix of fiber types for YOUR goals will then be stimulated without you ever needing to know about slow twitch, fast twitch, whatever. If you want to be faster, run sprints. If you want to be stronger, lift heavy. If you want endurance, do cardio (but get strong first). Whatever you do, don't organize your training around "fiber types."