Originally Posted by
bruce19
Well, according to "Cycling Past 50" p. 74-75 the best sprinters, who can spin at 140 rpm, "typically have lots of fast twitch muscle."
You're are mixing two different concepts. Fast twitch muscles are used with short bursts of speed like sprinting. Slow twitch are for endurance.
When you spin, it's an aerobic activity and relies mostly on slow twitch in an aerobic mode. Sprinting is an anaerobic activity and relies primarily on fast twitch fibers. Sprinters naturally have a higher percent of fast twitch than do non-sprinters.