As a race, blacks have more muscle mass, especially in the lower back, glutes and thighs. But there is more to that explanation also. There are two types of muscle fiber "slow twitch" and "fast twitch". Slow twitch fibers are slower but are better for endurance activities. Fast Twitch fibers activate quickly and are good for jumping and sprinting, but are not good for endurance activities. The average person has a 50/50 mix of fast and slow twitch muscle fibers in their body, but of course this ratio will vary from individual to individual, depending on genetics, and the effects of long term training.
Blacks of West African descent have predominantly fast twitch fibers in their body. The body composition of fast twitch fibers in this group is as much as 90% to even 100% fast twitch fibers. Ergo, this is why so many blacks are great jumpers and sprinters.
But what about the Kenyan and Ethiopian long distance runners you may ask? These blacks have a good deal of muscle mass as well, and long legs. But these blacks are of East African descent and do not have the predominantly fast twitch fibers in their body as the blacks of West African descent. And because of their lifestyle growing up in East Africa (long distance running, high grain and cereal diet) have developed slow twitch endurance fibers as a long term result of their lifestyle and training.
