I've wondered about Serena
Bob Mould (yes, that Bob Mould) talks about steroids in baseball and makes an interesting point:

So you sports fans know: when someone goes down with torn quadriceps, triceps, etc., it's likely a result of steroid use. The ligament cannot grow to support the extra mass, and the muscle tears from the bone - ouch is right. Where is Serena?

I've wondered about her. Her sister is tiny and doesn't seem to be able to put on muscle like Serena. It is entirely possible that it is just a genetic difference between the two siblings. Serena is surely, um, gifted in other ways compared to Venus besides her muscles. But you have to wonder.