Black men do not have extra muscles in their legs, states Dr. Robert Kwok on HealthTap. Basic muscle anatomy is not affected by race or gender. The human race arose from common ancestors, and separate races did not develop until migration occurred.
Although black athletes hold more world records for 100-meter dashes than any other race, LiveScience states that it has nothing to do with the color of their skin and is likely due to the longer length of their legs in relation to their torsos and their higher centers of gravity. Black men may have longer muscles in their legs, but not extra ones.