Read the article featuring Ryan Deak in the Denver Post and I was struck by his comment that after an hour and a half of running you begin "converting your fast twitch fibers" (presumably to slow twitch fibers). This theory sounds vaguely familar to something I heard years ago in an exercise physiology class. My questions are:1) Is Ryan right? 2) How much is converted?; 3) Why would distance runners want to convert their "precious-few" fast twitch fibers-can't we just improve the aerobic capacity of our slow twitch fibers without losing our fast twitch fibers?