Given that racists and slavers used the “natural physical strength” of black people to justify putting them on hard labor and some medics still think that blacks has higher resistance to pain, I wonder if when black athletes started to join mixed race sport teams, some racist would have used the same “biological advantage” argument that now transphobes use against trans athletes to claim it was “unfair” for black to compete against whites to justify segregation.
While there is no extra muscle, it is factually true that people of West African descent tend to have more fast twitch muscle fibers which is a pretty big advantage in many sports.
This is likely why the myth of the extra muscle originated.