people with african heritage, are naturally stronger and more athletic in my opinion. They run faster, further...are stronger.
Serena probably looks like she does due to her genes as well as specific strength training to have the edge in power . African woman are tended to be very strong and large boned (even her dad looks like he could be strong and big boned) - not trying to sound racist or anything...but this is often the case.
This thread should rather be:
who's stronger: Serena or Navratilova?