erm, no. hes saying that if you do training sessions with lots of lactic acid buildup, your body will tend to adapt towards a slow twitch machine, even if you do sprint sessions on other days. and by sprints i mean real sprinting sessions, like 5x60 with 6 minutes rest between runs. none of this 'i sprint a lap and then i walk a lap!' crap. thats not sprinting. theres a lot of reasons for that. one, the body recovers from me-tabolic fatigue faster than cns fatigue. two, the bodys muscles adapt towards the stimuli theyre given. if a man with pure slow twitch muscles is trained only as a weightlifter, eventually his slow twitch muscles will convert. the same goes for someone with only fast twitch muscles running marathons. since slow twitch sessions can be trained more often, its easier to convert.
there is a middle ground, but it is biased towards slow twitch (which was baggetts point). ill give you an example. say you take an elite 100/200 runner and an elite 800/1600 runner. the 800/1600 guy will probably be able to run a 200 in 21 or 22 seconds, which is 80-90% of the WR. but if you take the 100/200 guy, i HIGHLY doubt hell break 5:00 in the mile (<75% of the WR).