West African men have a higher ratio of fast twitch muscle fibres to slow twitch fibres then caucasian men (or men of any other ethnicity) have you ever noticed that east Africans are not sprinters but long distance runners? they have a greater proportion of slow twitch fibres. It isn't totally biological though, countries like Jamaica (not west Africa i know...but descendants of them) that have a history of performing well in such events have more of their top athletes going into such disciplines.