You are training to run a marathon in six months. which type of muscle fiber would be most beneficial for you to develop? a) slow twitch fibers, because they can contract for long periods of time without fatiguing b) fast twitch fibers, because they contract quickly and powerfully c) fast twitch fibers, because they primarily use aerobic respiration d) slow twitch fibers, because they contain more sarcoplasmic reticulum, allowing fast contractions