How important is a endurance base for a 400m sprinter?

For instance the need to do 600m runs etc, will this be even more important if the sprinter is better responsive to longer distances?|||an endurance base is not really important for sprinters, as sprinting uses a lot of fast-twitch muscles, which you are born with and can't really recruit any more of, and an endurance base will work to recruit your slow-twitch muscles.